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ChrisCwmbran
June 6th, 2012, 12:57 PM
More questions from me, re my Kaypro II this time.

The machine was completely untested so I took the top off and took a look inside. Everything is relatively clean and looked in order, so I decided to try powering it on!

The floppy drives made sounds consistent with whirring, and then two loud electrical cracking noises and a big cloud of smoke! :(

I think one flash came from the horizonal board below the back of the tube, and one from the vertically mounted board on the back of the machine.

Advice please?

How can I ensure there is no residual charge in the thing, so I can safely take the main board out to examine the two smaller boards?

Thanks again!

Chuck(G)
June 6th, 2012, 01:12 PM
Could well be some tanalum caps going. If you're not certain, use your eyes and nose to find what went wrong. There are service manuals on Bitsavers and they're pretty good.

ChrisCwmbran
June 6th, 2012, 01:20 PM
My biggest initial concern is how to make sure the circuitry in the machine doesnt have major charge in to give me a shock. I can't find consistent information on ensuring this really though, and until I'm pretty sure it has no shock surprises for me Im hesitant to proceed too far! :)

Chuck(G)
June 6th, 2012, 01:29 PM
Stay away from the mains connections while the system is powered on. Anything else may give you a "tingle", so keep one hand in a rear trouser pocket when you're fiddling around in a powered-on unit. That makes it extremely unlikely to create a path through your body that involves your heart

If memory serves, the Kaypro has a mains input filter that uses those terrible Rifa metallized paper capacitors (look like a block of clear epoxy) that tend to go BOOM when they get old. I'd start there first.

ChrisCwmbran
June 6th, 2012, 01:31 PM
Stay away from the mains connections while the system is powered on. Anything else may give you a "tingle", so keep one hand in a rear trouser pocket when you're fiddling around in a powered-on unit. That makes it extremely unlikely to create a path through your body that involves your heart

If memory serves, the Kaypro has a mains input filter that uses those terrible Rifa metallized paper capacitors (look like a block of clear epoxy) that tend to go BOOM when they get old. I'd start there first.

Do I not need to worry about capacitors on the power supply or CRT etc retaining charge when the machine is off?

Chuck(G)
June 6th, 2012, 01:36 PM
Do I not need to worry about capacitors on the power supply or CRT etc retaining charge when the machine is off?

The charge usually bleeds off pretty quickly, with the exception of the CRT anode connector--that thick wire with the rubber cup on the end of it Here's a procedure should you need it (http://www.stickycarpet.com/pinx/md.html).

ChrisCwmbran
June 6th, 2012, 02:51 PM
I've removed the logic board, and can see somewhat more inside the machine now.

The board that is mounted horizonally and connects directly to the CRT looks to be intact, though I thought it flashed and cracked just before the power board did (less than a second maybe).

The power supply board appears to have a capacitor that is blown apart - I'll remove the board and take photos tomorrow. Oddly on the face of it the fuse appears to still be intact!

I did notice that on the logic board the 4564N-25 RAM chips in sockets U20 thru U27, one of the two Z80s and the two 8242 chips have some corrosion on their pins. I have no idea why its only these specific chips. Tips on how to deal with this?

Chuck(G)
June 6th, 2012, 02:56 PM
I did notice that on the logic board the 4564N-25 RAM chips in sockets U20 thru U27, one of the two Z80s and the two 8242 chips have some corrosion on their pins. I have no idea why its only these specific chips. Tips on how to deal with this?

If they're in sockets, push them in to make sure they're seated. If not don't worry about it. If they're in sockets and you don't like the appearance, clean the crud off with a pencil eraser.

antiquekid3
June 6th, 2012, 03:53 PM
Wasn't it TI that had a big problem with metal whiskers on their pins? I think NASA was very angry with their metallurgical processes.

Chuck(G)
June 6th, 2012, 05:33 PM
Yeah, if you have a bunch of those old TI sockets, save them for your $10K Apple I replica... :)

I hated TI sockets. When I discovered Augat machine-pin sockets, I quit looking...

ChrisCwmbran
June 7th, 2012, 02:53 AM
The power supply board is an Astec AA12350. The capacitor that blew is C2, and C1 and C13 are possibly questionable in my view:

9232923392349235

Unfortunately C2 is so shattered I dont know what value and type it is at all. Anyone know?

Do people agree it looks like C1 and maybe C13 are also gone?

Clearly they are 0.01uF capacitors, but what is the full description of the three parts I need to order?

Also, are they of the same values as I'll find in my other stuff such as BBC Micros, and accordingly should I order a number of each?

ChrisCwmbran
June 7th, 2012, 05:13 AM
As far as I can see, C1 and C13 are "Capacitor X2 10nF 275V 18x5x11mm" according to RS Components here (http://uk.rs-online.com/web/p/plastic-film/7257483/?searchTerm=725-7483&relevancy-data=636F3D3126696E3D4931384E525353746F636B4E756D6 265724D504E266C753D656E266D6D3D6D61746368616C6C267 06D3D5E5C647B337D5B5C732D2F255C2E5D5C647B332C347D2 426706F3D313426736E3D592673743D52535F53544F434B5F4 E554D424552267573743D3732352D373438332677633D4E4F4 E4526).

From what I can glean it appears C2 was almost certainly "Capacitor X2 100nF 275V 18x6x12mm" and is just a larger size from the same range.

I hope Im right - I ordered some of each :)

Chuck(G)
June 7th, 2012, 08:22 AM
That's what the schematic says. The hated Rifa caps as I noted before.

Oddly enough, these are sometimes referred to as "safety" capacitors--not for not exploding, but failing in a predictable way so as not to endanger the user if they fail.

But we've been here before, I believe.

MikeS
June 7th, 2012, 09:30 AM
...But we've been here before, I believe.And will be again, I'm sure...

Does it work with those caps removed?

ChrisCwmbran
June 8th, 2012, 05:40 AM
Does it work with those caps removed?

Do you mean can we remove the need for them? I dunno! Chuck is much more of an expert than me!

Right I have received my bags of new capacitors. How do I tell the polarity of these? It doesnt appear to be marked!

MikeS
June 8th, 2012, 07:25 AM
Do you mean can we remove the need for them? I dunno! Chuck is much more of an expert than me!Assuming nothing else is wrong, the computer should work just fine without them.


Right I have received my bags of new capacitors. How do I tell the polarity of these? It doesnt appear to be marked!They're connected across alternating current, so they're non-polarized; I assume they are type X2 ?

ChrisCwmbran
June 8th, 2012, 07:46 AM
They're connected across alternating current, so they're non-polarized; I assume they are type X2 ?

Yes they are! Thanks for that info! Maybe today will see my Kaypro return to operational state! Fingers crossed!

If anyone wants to see the pics of the blown up capacitor they are on my website in the blog.

ChrisCwmbran
June 9th, 2012, 05:35 AM
Right I've reassembled the machine having replaced the 3 capacitors.

When it's turned on now I hear what sounds like a whirring noise but I think it's electrical.

I disconnected the power connector from the logic board and the values read are as follows:

-12 is reading -3.51v
+12 is reading 0.03v
+5 is reading 0.18v

Ideas please?

I thought the chirping was coming from the CRT but having unplugged the video card I'm now pretty sure its coming from the PSU.

Chuck(G)
June 9th, 2012, 08:54 AM
Well, at least things aren't blowing up on you. I think the Astec supply will operate without a load. Have you tested it with nothing plugged into it?

We need to figure out what part of your system is the problem.

ChrisCwmbran
June 9th, 2012, 09:51 AM
Testing the PSU on its own not connected to anything its still chirping.

The -12v pin is stable at -12.5v .

The +12v is varying constantly between about 7v and 12v by the look of it.

Similarly the +5v is varying between 3.8v and 5v or so. Its obviously hard to say because the display of the meter only updates at a certain speed.

nige the hippy
June 9th, 2012, 09:59 AM
The PSU is probably initially overloaded, but checked off load is over volting! Probably shorted by a tantalum capacitor somewhere on one of the boards. Check the power supply on some sort of dummy load on the 5V rail (e.g. a 12V 50W headlight, or halogen bulb) that should load it sufficiently to check everything.

nige the hippy
June 9th, 2012, 10:03 AM
If the psu is ok, You now may have to find the shorted cap. this is where a low-ohms meter, or current tracer probe comes in really handy. Failing that use a "normal" meter & take a best guess.

ChrisCwmbran
June 9th, 2012, 10:06 AM
I'm not sure what you mean by a low-ohms meter. This is what I have:

http://www.uni-trend.com/ut70d.html

Chuck(G)
June 9th, 2012, 10:10 AM
You might try the PSU with a light load on it--say, a small hard drive--but leave the motherboard off for now. I don't expect the PSU to behave differently, however.

Seeing has how this thing is nearing 30 years in age, my first suspect would be the capacitors. They may not be bulging, but they could well be dried out inside. If you have a capacitor tester, that's great, but given the age, I'd probably re-cap all of the electrolytics as a start.

Also, see this excellent guide (http://www.repairfaq.org/sam/smpsfaq.htm) on trouble-shooting SMPSUs.

ChrisCwmbran
June 9th, 2012, 10:53 AM
To what extent are devices such as this:

http://www.peakelec.co.uk/acatalog/jz_esr70.html

good for testing capacitors? It says it can measure the ESR of a capacitor when it's in circuit and I get the impression that they think ESR is an indication of the state of a capacitor?

Im somewhat concerned that given the number of machines I have, I dont want to replace caps that don't need it or over time I'll waste a fortune.

ChrisCwmbran
June 10th, 2012, 02:55 AM
Chuck, could you possibly post a copy of the schematic for the PSU board please? I've found the technical reference manual which appears to have the logic board schematics but not the power schematics.

nige the hippy
June 10th, 2012, 03:28 AM
I would have thought that the capacitance is more usually a good measure of the state of a capacitor!
Although I'm not sure, I would think that low ESR is down to the construction / materials. If the capacitor is getting hot in service then it's ESR (Equivalent Series Resistance) may have gone up.
Your meter will measure capacitance up to a point, a way of fairly accurately gauging large capacitors in circuit is to charge them up with a constant current supply & time them to a particular voltage Q=CV=IT, although you can get a good impression with an ordinary DMM on diode test, by gauging the time it takes to reach maximum test voltage (obviously reverse bias the rectifier diodes!).
An old fashioned moving coil meter on ohms will also give a good indication, by how quickly the pointer moves, but check polarity on the probes, it isn't neccessarily positive probe positive on ohms.

Chuck(G)
June 10th, 2012, 09:18 AM
On large electrolytics, I've found that the easiest way to test for a dried-out electrolytic is to tap it. Dried-out electrolytics have a different "hollow" sound that good ones. Not very scientific, I know, but it's a quick, rough test.

ESR is less important in this case, as that's mostly a choice of the original designer. Capacitance and leakage are everything when troubleshooting an existing design. I'd never rely on an in-circuit tester for electrolytics. Quite often, designers parallel filter capacitors, so if you get a low value, you don't know which it is.

I believe that the Osborne 1 uses the same (or very similar Astec) PSU. So if you need a schematic, you can find it in the Osborne service manual (http://bitsavers.org/pdf/osborne/2F00040-00_Service2ndEdition_1983.pdf).

ChrisCwmbran
June 10th, 2012, 10:54 AM
Am I right that capacitors with a higher ripple current value are higher quality?

What does the leakage current value mean?

I can for example in the case of the 100uF 250v caps that the price varies between 0.65 and 2.58. Any tips for chosing the best choice?

Chuck(G)
June 10th, 2012, 12:28 PM
I'll try to make it simple.

No capacitor (or any other real-world device) is perfect. Any capacitor will exhibit some resistance (and inductance). So, if you charge a capacitor to a voltage, you'll find that the charge will slowly dissipate because of the capacitor's internal resistance. This characteristic is known as leakage current. High leakage currents are undesirable--they cause internal heating as well as negate some of the capacitance properties. Note that we're talking about a virtual resistor in parallel with the capacitance.

However, there is also a virtual resistor in series with the capacitance. Its value is known as the ESR or "effective series resistance".

When used in power supplies, most capacitors are used to smooth out a small AC current superimposed on a DC current. e.g.:

http://www.eecs.tufts.edu/~dsculley/tutorial/diodes/fullWaveOut.jpg

A filter capacitor, being the beast that it is, will tend to resist changes in voltage, so it settles down to alternating charging on the peaks and discharging on the valleys so that the DC voltage settles out to something between the two. Note that this necessarily involves a flow of current in and out of the capacitor. Remember the ESR? Some of the energy from this current flow will be dissipated in the virtual series resistance. Since power P = IR, a high ESR is not terribly desirable, as more power will be lost as heat in the capacitor, which will shorten its life. (In fact, heat is probably the single most significant factor in the demise of electrolytic capacitors). Note that ESR has no relationship to actual capacitance; it's just a side-effect of living in the real world.

As far as choosing capacitors, I stick with the Japanese brands. Nichicon, Rubycon, NCC, Panasonic, etc. I've been burned by Chinese capacitors more than once, so I generally steer clear of them.

ChrisCwmbran
June 12th, 2012, 07:23 AM
Thanks for explaining that!

I've made a mess of things here. Some of the caps I've ordered in have smaller pin spacing than the ones they are replacing. Im assuming I should change them rather than using more lead and making do?

Chuck(G)
June 12th, 2012, 08:53 AM
As long as the ratings are the same (working voltage and capacitance), don't worry about it. Things get smaller as technology advances.

Do be careful to observe polarity, however!

MikeS
June 12th, 2012, 09:16 AM
I think you might be off on the wrong track; did you test it with a load as Nige suggested in post #21?

It certainly looks like the PS might be OK, shutting down when connected because of a short somewhere on the system board and with no load cycling on and off due to overvoltage. Try it with a load of some kind, an old hard disk, light bulb, whatever, before perhaps needlessly replacing those caps.

Also measure the resistance to ground of the system board's power supply connections.

tezza
June 12th, 2012, 10:13 AM
My gut feeling says a short on the system board also. Certainly worth investigating.

Tez

ChrisCwmbran
June 12th, 2012, 10:22 AM
Having replaced the caps, I powered the PSU on without anything connected to it and C22 fried itself.

There was no sign of a chirping though.

Ok ignore that - human error.

Will try again once I've eaten.

ChrisCwmbran
June 12th, 2012, 11:20 AM
Ok fed and happier now :)

I've rectified my error. With the PSU board not connected to anything the results are the same as they were before we started this excercise. Oh well the caps didnt fix it but its all good learning for me.

I connected the system board Gnd pin to the +12v pin and there was no connection. The same applies to the -12v pin and Gnd, however when the +5v pin and ground are measured, I show a resistance of marginally above 300 ohms.

Chuck(G)
June 12th, 2012, 01:47 PM
Well, I did suggest testing it with a load.

5V / 300 ohms = 160 ma., well within the capabilities of the supply and probably not enough to keep the supply happy. Looking at the schematic, you should be drawing more than that. Is the 5V steady?

MikeS
June 12th, 2012, 02:04 PM
Well, I did suggest testing it with a load.As did Nige, but with all that discussion about ESR, leakage, ripple etc. and replacing the line filters, which, although interesting, is not necessarily relevant to finding the actual problem, I didn't see where he had actually tested it with a load other than the possibly defective system board.

ChrisCwmbran
June 12th, 2012, 02:13 PM
Ah at 300 ohm reading might be a red herring. I think I misunderstood you. That is the reading between the ground and 5v pins of the logic board with it not connected to anything.

So to clarrify you want the readings at the pins on the logic board when the power board is powered on and connected to the logic board? Do you want the video board disconnected whilst I do this? If so, I assume you want me to remove the edge connector from the video board, and the cable that runs from the video board to the logic board?

I don't have anything to use as a suitable load so Im heading to the store tomorrow to get some suitable bits. I have very little in the way of loose wire etc.

Chuck(G)
June 12th, 2012, 02:35 PM
Do you have a place near you that carries incandescent bulbs for autos? They're great for making dummy loads. I like the so-called "festoon" bulbs.

Something like a 211 lamp will draw about an amp at 12V and about the same at 5V, which should be enough of a load.

ChrisCwmbran
June 12th, 2012, 02:36 PM
Do you have a place near you that carries incandescent bulbs for autos? They're great for making dummy loads. I like the so-called "festoon" bulbs.

Something like a 211 lamp will draw about an amp at 12V and about the same at 5V, which should be enough of a load.

I have an Audi bulb in it's little holder but I'm going to the store to get some wire etc tomorrow.

MikeS
June 12th, 2012, 03:47 PM
So to clarrify you want the readings at the pins on the logic board when the power board is powered on and connected to the logic board?No, we want to know what the voltages are on the +5V and +12v pins on the power supply when it is disconnected from the system board and a light bulb or similar load is connected instead between those pins and the common.

I'm a little confused; you said

I disconnected the power connector from the logic board and the values read are as follows:
-12 is reading -3.51v
+12 is reading 0.03v
+5 is reading 0.18v
and then you said

Testing the PSU on its own not connected to anything its still chirping.
The -12v pin is stable at -12.5v .
The +12v is varying constantly between about 7v and 12v by the look of it.
Similarly the +5v is varying between 3.8v and 5v or so.
Sounds like the PS is disconnected in both cases but the voltages are different?

Be careful; everyone warns about the high voltage on the CRT, but the really dangerous currents are in the power supply.

ChrisCwmbran
June 13th, 2012, 01:55 PM
Ok. Cables made up nicely :) Power supply board removed from unit, and connected to mains supply, and a car headlight bulb connected across the 5V and Gnd pins of the power supply board.

Readings:

5v reads 4.81v
12v reads 13.64v
-12v reads -12.40v

No chirping. All steady.

Same bulb connected across the 12V and Gnd pins of the power supply board.

5v reads 3.8v
12v reads 0.30v
-12v reads -4.8v

PSU chirps happily at high speed.

nige the hippy
June 13th, 2012, 02:08 PM
That sounds pretty well as you'd expect, Usually the supply will monitor the 5V rail & adjust itself so that that is ok & the other voltages follow as best they can. 5V is a little low (still within TTL spec), it could be the smoothing capacitors on the 5V rail & if you can get a ripple measurement (in the absence of a scope try AC Volts on your meter - It should work but it won't be dead right because the meter is set to measure RMS (on a sine wave at about 50 Hz too)) but if it's less than 0.25V (RMS) you should be just about ok.

ChrisCwmbran
June 13th, 2012, 02:17 PM
Well, I do have.....

9363

But I've old just got it and not used it yet. I do know its in good working order though.

Should I go for the meter or does anyone have any hints on how to use this?

Chuck(G)
June 13th, 2012, 02:28 PM
Okay, now let's go back to your motherboard.

FIrst of all, verify the connection between the +5 pin on J7 and pin 8 on any 14-pin DIP on the board. Should be very clear continuity. If not, inspect the solder connections for J7 (where the cable from the power supply plugs in). Make sure that it's good--and trace the +5 as far as you can.

If that all checks out, check the cable that goes from the power supply to the motherboard.

ChrisCwmbran
June 13th, 2012, 02:32 PM
Are you sure you mean J7 and not J5? J5 is the connector where the PSU connects to the motherboard. J7 is a 3 pin connector where none of the pins are marked. (Just checking)

ChrisCwmbran
June 14th, 2012, 05:09 AM
With the power supply board removed completely from the machine I connected the power board to the mains, and applied my bulb as a load on the 5v rail. I then connected my scope across the 5v and ground rails on the power board:


http://youtu.be/xu2gLI_a1SI

When I press "Measure" the scope tells me I have a Pk-Pk of around 13mV.

Am still examining the logic board.

Chuck(G)
June 14th, 2012, 07:54 AM
J5 it is--I was relying on my (somewhat faulty) memory.

I take it that the bulb on the 5V line doesn't light up at all.

ChrisCwmbran
June 14th, 2012, 08:02 AM
The bulb glows dimly when connected to the 5v line, and the voltages are all relatively stable.

ChrisCwmbran
June 14th, 2012, 12:26 PM
FIrst of all, verify the connection between the +5 pin on J7 and pin 8 on any 14-pin DIP on the board. Should be very clear continuity. If not, inspect the solder connections for J7 (where the cable from the power supply plugs in). Make sure that it's good--and trace the +5 as far as you can.

Ok so you mean J5 rather than J7. Are you counting your pins anti-clockwise from pin 1?

ChrisCwmbran
June 14th, 2012, 12:40 PM
I'm guessing what you call pin 8 is the opposing pin in the pair with pin 1 - although according to Wikipedia thats actually called pin 14???

Anyway, assuming we are talking about the same pin, every 14-pin DIP on the board with the exception of one has this pin connected to 5v. The one exception being U68 which appears to be a MC1488N, and its pin connects to the 12v pin.

MikeS
June 14th, 2012, 03:06 PM
:wallbang: :confused5: :confused3:

MikeS
June 14th, 2012, 06:37 PM
Hope I didn't offend or insult anyone; just expressing my frustration following these 50 posts and the confusion, contradictions, etc. that this kind of troubleshooting often entails (not to mention the confusion of Kaypro model numbers).

Can we finally take it that the power supply is functional and in fact has been all along?
I.e.:
With nothing connected to the PS except AC in, the 5V and 12V outputs read ~3-5 and ~7-12V respectively.
With a light bulb across the 5V, the 5V output reads a steady ~4.5-5V, the bulb glows dimly, and +12V and -12V are also close.
With the system board connected the 5V and 12V outputs read close to 0.

Is that correct?

Notice that the scope is set to measure AC voltage, i.e. just the noise on the 5V line.

When you measure resistance to ground on the 5V, +12V and -12V pins on the system board when disconnected from the PS, you get infinite resistance on the 12V lines and around 300 Ohms on the 5V line? What range? In both directions?

When you're talking about P5, P7 etc. and Wikipedia, which schematics are you/we looking at? I thought the PS connector is a straight in-line connector, so what's the [counter]clockwise referring to? And pin 8 of the 14-pin DIPs?

The schematics I'm looking at call the power supply connector J7, as Chuck said; what and where is P5?

Assuming all the above is correct, let's finally see why the system board shuts down the PS. Have you inspected the usual culprits, any tantalum caps?

Chuck(G)
June 14th, 2012, 06:47 PM
Sorry, I've been out wrestling with a chainsaw. I still have lots of cleanup to do from the snowstorm on the first day of spring.

At any rate, Mike, do you want to lead Chris through this? I'm having a problem assuming that Chris has some experience in this stuff. No offense to Chris, of course--I'm just not used to working this way.

MikeS
June 14th, 2012, 06:56 PM
Sorry, I've been out wrestling with a chainsaw. I still have lots of cleanup to do from the snowstorm on the first day of spring.Ah the joys of living the life of the country gentleman in the rustic Northwest...
As a matter of fact I have a few downed trees as well, but they're a little big for me and my puny electric chainsaw.


At any rate, Mike, do you want to lead Chris through this? I'm having a problem assuming that Chris has some experience in this stuff. No offense to Chris, of course--I'm just not used to working this way.Aw, don't go; once we straighten out what's what and are all on the same page looking at the same schematics it oughta be a breeze. Unfortunately my Kaypro is out on loan, but it's a 2x, somewhat newer; don't know how similar they are.

Chuck(G)
June 14th, 2012, 07:08 PM
Ah the joys of living the life of the country gentleman in the rustic Northwest...
As a matter of fact I have a few downed trees as well, but they're a little big for me and my puny electric chainsaw.

Today I was out with my Stihl 056 Super--a beast of a saw, but it sure makes the chips fly. Big oak log shifted and broke the bar tensioning bolt, so it's out of commission until I get a new one installed. I have an 032AV, but it's being stubborn about not wanting to run. So it's back to the Mac 610--not in the same league, but it'll get the job done, just slower.


Aw, don't go; once we straighten out what's what and are all on the same page looking at the same schematics it oughta be a breeze. Unfortunately my Kaypro is out on loan, but it's a 2x, somewhat newer; don't know how similar they are.

From what I can tell, the 2X is pretty close in the mainboard department, but I'll have a close look at the schematics if there's any doubt. That 300 ohm continuity test Chris did on the +5 to ground on the motherboard doesn't sound right to me.

ChrisCwmbran
June 15th, 2012, 02:44 AM
Hope I didn't offend or insult anyone; just expressing my frustration following these 50 posts and the confusion, contradictions, etc. that this kind of troubleshooting often entails (not to mention the confusion of Kaypro model numbers).

You didn't Mike - at least not me. I'm quite confused by this thread in points. Maybe at some points I've been far from clear, however I object the implication that I'm some kind of newbie made by Chuck. I've been using and working with computers since 1981 (as a teenager). I appreciate Chuck has been trying hard to help, and that it isnt easy in these situations, but I don't think I have been the only source of confusion.


Can we finally take it that the power supply is functional and in fact has been all along?

Whilst I think we have now established that replacing the electrolitic capacitors on the board was unnecessary, and that the board now appears to work correctly, the three X2 capacitors we definitely blown in the beginning - one to little pieces. I think we can say that despite peoples uncertainty that the Kaypro II powersupply does require a load.



I.e.:
With nothing connected to the PS except AC in, the 5V and 12V outputs read ~3-5 and ~7-12V respectively.
With a light bulb across the 5V, the 5V output reads a steady ~4.5-5V, the bulb glows dimly, and +12V and -12V are also close.
With the system board connected the 5V and 12V outputs read close to 0.

Is that correct?

Yes.


Notice that the scope is set to measure AC voltage, i.e. just the noise on the 5V line.

According to the guide I read on using a scope to measure ripple current they said thats what I should do because it effectively removes the +5v DC component from the signal, and accordingly allowed us to measure the degree of variance in the signal. I thought that is what Nige wanted me to do?


When you measure resistance to ground on the 5V, +12V and -12V pins on the system board when disconnected from the PS, you get infinite resistance on the 12V lines and around 300 Ohms on the 5V line? What range? In both directions?

I can do some more measurements in this area. To be honest I didn't think much about resistance because obviously a resistor isn't polarised - however thinking about it more there arent just resistors in the circuit we are measuring :(


When you're talking about P5, P7 etc. and Wikipedia, which schematics are you/we looking at? I thought the PS connector is a straight in-line connector, so what's the [counter]clockwise referring to? And pin 8 of the 14-pin DIPs?

The schematics I'm looking at call the power supply connector J7, as Chuck said; what and where is P5?

According to me, and clearly I may be wrong, this is the power connector, and it is called J5:

9377

J7 looks like this:

9378

Now I don't have a pinout for this, but in my experience (which I'd say is fairly considerable) I wouldn't call this a power connector.

Now when it comes to counter clockwise counting, I was talking about the pins on a 14pin DIP (example included just to ensure we are talking about the same thing):

9379

According to the Wikipedia page, as we look at it in that photo the bottom left pin is pin 1 and you count counter clockwise for pin numbers making the top right pin number 8. Now from what I understood Chuck wanted us to check the continuity between the 5v pin of the power connector (which in my opinion is called J5 but this post may be proving me wrong) and pin 8 of each of the 14pin DIP chips. Continuity between the 5v pin of what I call the power connector, and pin 8 of the 14pin DIPs does not seem to be consistent at all - however there does appear to be continuity between the 5v pin of what I call the power connector and pin 14 of the 14 pin DIPs (i.e. the top left pin according to me) for all chips except one which I noted in a previous post where it's pin 14 (by my definition) is connected to the 12v pin of the power connector.


Assuming all the above is correct, let's finally see why the system board shuts down the PS. Have you inspected the usual culprits, any tantalum caps?

9380

If I'm right (and I admit to being unsure on this front), C8 and C9, which are a slightly more brown colour are tantalum cap, I count 10 on the board in total, none of which appear to have a problem (visually).

The other capacitors such as C82 (Ceramic disk caps?) is different. There are two, C53 and C59 which are damaged or at least cracked:

9381

I can go get replacements for these but I don't really know how to describe these or what spec they are.

Thanks for taking the time to read this, and thanks for all of each of your help with it.

MikeS
June 15th, 2012, 10:48 AM
Chris, it's not going to help if you feel we're talking down to you and you get defensive. We can only go by what we read in your posts and it does seem that despite your years of experience in using and working with computers you don't have a lot of experience in troubleshooting electronics. So what; let's not waste any more time on that and focus on solving the problem.

Regardless, it's challenging enough when you have the equipment and the tools and instruments in front of you but much more so when you have to do it through the eyes and verbal descriptions of someone else, and misunderstandings are almost inevitable.

The X2 caps were definitely bad and should be replaced, but they don't affect the operation of the power supply and weren't really relevant to finding the real problem with your Kaypro. As Chuck said, they (and also your real problem of the PS shutting down) are common problems and discussed in dozens of threads on this forum.

You have the board in front of you and you're right, the power connector is labelled J5. On the other hand, we only have the schematics to go by and on the ones I (and Chuck, presumably) looked at it is labelled J7 (or J2). Have you managed to find a schematic that corresponds to your board and if so, where?

Since the issue is that voltages drop to zero when connected, we're just interested in DC voltages and don't really care about noise or ripple; anything really severe would show on a DC scope trace anyway.

Except for the electrolytic beside J7, all the caps in your pictures including C8 & C9 are disk ceramics and almost certainly irrelevant.

What we need to do is find out which of the power supply lines is drawing too much current, and why; this can be challenging if there are no visible clues.

So, to confirm once more: with the system board only connected to the PS (i.e. no video, floppy drives, keyboard etc.) are the 5V and +12V lines close to zero?

I'd suggest powering the 5V and 12V lines separately, but I suspect that might damage the RAM chips; anybody else have an opinion on this?

Are the RAM chips in sockets? If so, can you remove them and check the voltages again?

So, please measure the resistances to ground of each supply line again, in both directions and tell us the lowest ohms range that gives you a reading, if any.

ChrisCwmbran
June 15th, 2012, 12:09 PM
You have the board in front of you and you're right, the power connector is labelled J5. On the other hand, we only have the schematics to go by and on the ones I (and Chuck, presumably) looked at it is labelled J7 (or J2). Have you managed to find a schematic that corresponds to your board and if so, where?

Nope, only ones that call it J7 - I'm guessing in the same PDF documents you both have.


So, to confirm once more: with the system board only connected to the PS (i.e. no video, floppy drives, keyboard etc.) are the 5V and +12V lines close to zero?

I'll redo those tests on Sunday morning. I'm stuck in London tomorrow. What I'll do is put the power supply board and the logic board on the bench top, and do the tests using none of the actual Kaypro wiring. Thinking about it when I first tried stuff, the power board might have been effected by either the drives or the video card so by doing it externally it proves they aren't connected.


I'd suggest powering the 5V and 12V lines separately, but I suspect that might damage the RAM chips; anybody else have an opinion on this?

Are the RAM chips in sockets? If so, can you remove them and check the voltages again?

The RAM chips are socketed


So, please measure the resistances to ground of each supply line again, in both directions and tell us the lowest ohms range that gives you a reading, if any.

I'll re-do these resistances again on Sunday as well.

I appologise for getting grumpy with people. All my life I've had people bringing PCs to me to fix, and I admit until recently if I determined the PSU was playing up, I took the PSU out and fitted a new unit, as with the other parts of the PC. I did however do electronics qualifications but they were more than 20 years ago and havent been used in the meantime. I'd hope though that assuming I understand what people are saying I shouldnt need telling things more than once.

MikeS
June 15th, 2012, 12:41 PM
The RAM chips are socketed Excellent. After tantalum caps old RAM chips are the next likely culprit, so if the PS still shuts down with everything except the system board disconnected then remove them and see if that makes a difference.


I'd hope though that assuming I understand what people are saying I shouldnt need telling things more than once.I think it was more a question of Chuck and me not understanding what you were saying, but let's move on...

tezza
June 15th, 2012, 01:18 PM
Yes, reinforcing Mike's comment: Those AC Filter caps in early 80s computers often blow. It looks drastic and they smell awful. They need to be replaced of course but they usually don't stop the PSU from working.

I had an Apple IIe that had no sign of life and a clicking PSU. It was a shorted capacitor on the mainboard.

I'm sure you'll get there. Just a matter of methodically tracing the fault.

Tez

ChrisCwmbran
June 15th, 2012, 02:41 PM
I just found this document btw:

http://messui.the-chronicles.org/comp/kaypro_tm.pdf

A lot of it goes over my head really but some of you might find it very interesting - if you havent actually seen it before.

For machines like this, is finding replacement ram chips difficult or are modern equivalents still available?

ChrisCwmbran
June 17th, 2012, 10:06 AM
Right here's the test I have just done.

PSU board and logic board on bench.

Power (+12v, -12v, 5v and GND) connected from PSU to J5 of logic board using test leads.

Powered on. No chirping from PSU at all.

12v rail reads 12.76v

-12v rail reads -12.39v

5v rail reads 5.009v

Obviously I get no kind of beep or anything but I'm assuming the Kaypro has no kind of speaker to make a sound on the logic board.

MikeS
June 17th, 2012, 10:20 AM
There you go! It's fixed; congratulations! ;-)

Maybe a picture of the normal setup would help; why did you need test leads? How is the PS normally connected to the system board?

I assume this is with all the RAM chips in place?

So, unless it has indeed fixed itself presumably something else besides the system board is shutting down the supply; try connecting everything else one at a time and see if the voltages change.

ChrisCwmbran
June 17th, 2012, 10:28 AM
The "cable loom" in the case connects the two boards normally, but also would connect the video board and the drives hence the reason I used them externally with the test leads (just for simplicity).

Yes the test was done with RAM in place.

Tomorrow I'll put the logic board and psu board in the case, but disconnect the floppy drives, meaning all we have added to the equation is the video board/monitor. I have a feeling then we'll be chirping again - my suspicion is that the video card is more likely to be the problem than the floppy drives.

Unless you suggest I do something different?

MikeS
June 17th, 2012, 10:41 AM
As mentioned previously, tantalum caps are becoming the most common cause of this kind of problem, so inspect the video board carefully. The trouble is that they're not obvious until they explode; once they do (just like those line filter caps) the problem usually goes away, so if it is a cap in your case it hasn't exploded yet which will make it harder to identify.

Anyway, let's see what happens when you plug everything back in; maybe we'll witness a miracle... ;-)

Chuck(G)
June 17th, 2012, 11:08 AM
I'd also note that replacing tantalum caps that are used for decoupling with similar-value electrolytics is just fine. Where tantalums are used for timing, etc., their value stability is important, but usually those have smaller than usual values, under 10 F.

ChrisCwmbran
June 19th, 2012, 07:35 AM
Ok thanks for the advice.

Whilst waiting for time to test to see if the floppy drives or the video card are what is causing the PSU to reset, I've been thinking about the other issue I have in the Kaypro.

On the CRT there are a pair of what I would refer to as metal whiskers. I'm guessing they are some kind of grounding. Oddly they are the only thing in the machine that is corroded.

I have a couple of rust treatments, one of which is just for cleaning off rust, and the other turns corrosion into some kind of "strong as metal meterial" although it's not clear if this material is conductive or not.

Do I dare use either of these treatments on the whiskers? Is there something else I should do to treat them?

MikeS
June 19th, 2012, 06:58 PM
Sounds like the grounding fingers, although they're usually copper or brass; I'd just clean them and not worry about them.

ChrisCwmbran
June 24th, 2012, 07:45 AM
Finally had time to move on with this a little.

Step 1 - Perhaps unwise!

I decided that it wouldn't hurt to connect one of the floppy drives up to an ATX PSU and turn it on. Chose the one with the terminating block.

Turned it on.

Bang!

9466

Capacitor C36 exploded.

Feeling less confident I retreated and watched the Formula 1 GP from Spain.



Step 2 - Feeling calmer.

I got the PSU board for the Kaypro and connected it to the mains - chirp chirp chirp as expected. (No load).

I got the logic board and hooked it up to the PSU board. Turned it on - nice and silent as was the case when we established the PSU Board was working.

I disconnected the logic board, and connected the second floppy drive to the PSU to see if it was sufficient enough load. Power supply was nice and silent. I guess a floppy drive is enough of a load for the Kaypro PSU.

I then disconnected the floppy drive and put it out of the way.

This time I connected the logic board and the video board to the PSU. For a few seconds we heard nothing - no chirping and saw nothing. Then behold on the CRT we saw:


http://youtu.be/D-lxBml7K5U

Its a little hard to make out on the display but its largely batches of 0's and 1's. The was also the occaisonal click I think coming from the video board and you'll perhaps be able to make out a slightly brighter dot jumping around on screen.

Powered it off and back on. Exactly the same happened.

More advice welcomed please!

Oh, and I have the monitor and video board, disconnected from the rest of the computer sat here on my desktop but I'm affraid to move it in case it contains some massive charge in its caps. How long till it should be safe to move it? Im guessing it will be losing charge constantly?

MikeS
June 24th, 2012, 09:49 PM
Well, as we suspected all along it was a bad tantalum cap pulling down the power supply and you finally found it the traditional way, with a bang.

Considering how long it's taken us to get to this point, that video problem could take a while... ;-)

I wouldn't be so worried about residual high voltages; capacitors will generally discharge pretty quickly through their loads and the only thing that does retain a charge is the CRT. Although shocking it's actually pretty harmless; stay away from the CRT anode and the HOT/flyback and keep your fingers away from the power supply when it's turned on and you should be OK.

Some surprises in that race for sure; a few disappointed faces and one pretty happy and emotional one, not to mention a few after-the-fact penalties. One of the best seasons in years.

ChrisCwmbran
June 25th, 2012, 12:00 AM
Considering how long it's taken us to get to this point, that video problem could take a while... ;-)

So do you suggest I reassemble the system and ignore it, chuck it in the skip or?

The only thing I know I can do in this situation is try reseating the socketed ICs which of course is all of them. I can remove them all one by one and reseat them if you wish but it will take quite some time.

I presume the occaisonal click and brighter pixel could be caused by the proximity of the various boards to each other on the bench? After all in normal use in the machine there is that screening board (don't know the technical word sorry) between the logic board and the other two boards. Is it just a case of some kind of interference?

I also presume that the fact that the display is made up of properly formed characters, in blocks of 8 flashing on the screen must be a significant clue as to where the fault lies, but being of limited experience when it comes to diagnosing the actual electronic fault, this is just a logical guess.

ChrisCwmbran
June 25th, 2012, 03:05 AM
In the case of the blown capacitor in the picture two posts up (on the floppy drive) is that board made using a strange soldering technique? It looks like the joints are made from the top of the board i.e. the component side?

Can anyone confirm the specification of the capacitor please? Even on the other drive I cannot read what it says.

ChrisCwmbran
June 25th, 2012, 04:49 AM
Ok I found this thread:

http://www.vintage-computer.com/vcforum/showthread.php?20885-Trying-to-fix-a-Tandon-TM-100-2A/page2

Which implies C36 is probably a 4.7uF so Im gonna pick one or two up in town now.

Im still slightly unsure if this is normal through hole soldering or some other type. Please advise.

smp
June 25th, 2012, 06:12 AM
In the case of the blown capacitor in the picture two posts up (on the floppy drive) is that board made using a strange soldering technique? It looks like the joints are made from the top of the board i.e. the component side?


The soldering of the circuit board in the picture you reference looks perfectly fine. The board was probably put through a solder flow machine, rather than hand soldered. Everything (except the blown up cap) looks OK.

smp

ChrisCwmbran
June 25th, 2012, 06:16 AM
So do I desolder the blown cap from the underside as normal?

smp
June 25th, 2012, 07:32 AM
So do I desolder the blown cap from the underside as normal?


Yes. The assistance of Solder Wick, or a "solder-sucker" should help.

smp

MikeS
June 25th, 2012, 09:20 AM
Ok I found this thread:

http://www.vintage-computer.com/vcforum/showthread.php?20885-Trying-to-fix-a-Tandon-TM-100-2A/page2

Which implies C36 is probably a 4.7uF so Im gonna pick one or two up in town now.

Im still slightly unsure if this is normal through hole soldering or some other type. Please advise.Yup, definitely a Tandon TM100 and a 4.7uf/16V tantalum cap; normal soldering, observe polarity.

MikeS
June 25th, 2012, 09:27 AM
Re the video problem, reseating the chips is always a good idea as long as you don't bend or break a pin in the process. Sometimes you can just slide the chips back and forth sideways a bit instead of removing/replacing them.

The click could be an occasional HV flashover on the CRT or HOT; try watching the back of the screen in the dark to see if you see any flashes anywhere when it clicks.

I doubt that the absence of shielding is an issue, but you're right that what's displayed could be a significant clue; any chance of a closer picture?

ChrisCwmbran
June 25th, 2012, 01:14 PM
I've connected everything back up and tried to get some better pictures:

9474

9475


http://youtu.be/Ot9EhEfPxBw

Having run it in the dark there was no sign of any flashes or arcing on the back of the tube, or the video board.

Sorry the pictures arent very good - I hope it does show though that the stuff is largely formed from proper characters not just random dots etc.

ChrisCwmbran
June 27th, 2012, 12:44 AM
Is the problem likely to be the video board here or is it more likely to be the video section of the logic board?

If we think the video board is ok Im thinking it would be a good idea to put the boards etc back into the case on the basis that the logic board is easily accessible when it is generally back together.

I've sourced replacements for all the screws in this machine - mostly stainless. I find quite often the heads of screws are quite rusty I guess where screwdrivers have damaged the galvanistion on the screws. They should arrive tomorrow.

ChrisCwmbran
June 28th, 2012, 05:33 AM
Of the two Tandon TM100 floppy drives, is the A: drive the one with resistor shunt thinggy or the other one please?

I know I should have written this down - could have sworn I did but can't find it.

Maniak
June 29th, 2012, 09:01 AM
I just popped the top on my Kaypro II to double check this. Drive A is on the middle of the cable. Drive B is at the end of the cable AND has the terminating resistor.

~Mark

MikeS
June 29th, 2012, 09:50 AM
Of the two Tandon TM100 floppy drives, is the A: drive the one with resistor shunt thinggy or the other one please?

I know I should have written this down - could have sworn I did but can't find it.Maniak's probably right,but FYI the terminating resistor has nothing to do with Drive A or B; although it's not critical it should go on whichever drive is at the end of the cable.

Drive A or B are determined by a DS jumper; on the TM100 it's usually a DIP jumper plug with one or more links cut:

9499

ChrisCwmbran
June 29th, 2012, 10:19 AM
Thank you both very much :)

ChrisCwmbran
June 30th, 2012, 03:51 AM
These drives weren't connected when any of the tests (other than the individual drive tests were done) but today I noticed something:

9502

9503

The first image is th Drive B, and the second is of Drive A.

On the first image you can clearly see where the capacitor that we think was shorting the whole system, and blew when the drive was tested.

On the second image there is something very very odd about the way in which the connectors 8, 9 and 10 have been connected.

These have never been disconnected and were like it when the machine came to me.

I assume this is wrong and needs correcting.

Does this throw any light on what the problem with the logic board is? i.e. would this have blown a specific chip on the logic board?

MikeS
June 30th, 2012, 05:34 AM
Good catch! Drive A is almost certainly connected incorrectly, there should be gaps between 8 & 9 and 10 & 11 as per drive B.

Those are the LED, the index sensor and the WP switch; possible but unlikely that it damaged the drive, but extremely unlikely that it would have damaged the system board.

Looks like someone's been poking around before you; that always makes troubleshooting more, umm, interesting...

ChrisCwmbran
June 30th, 2012, 02:56 PM
Right, I've returned all the parts except the two floppy drives to the original case for their own protection, and for ease of working on the logic board.

Ive tried wriggling all the chips a bit, and pressing down on them, but when the machine is powered on, all it does is the same displays as above.

I guess now I have to begin reseating? Any tips where to start?

Ive printed the schematic for the logic board. Its three pages: CRT control, CPU and memory, and IO/Disk controller, but I can't really decide which area of the board to start.

On the floppy drive front btw, I've replaced the blown capacitor, and put a bit of silicon grease on the rails carrying the heads ready for their return to the machine. I've also corrected those connectors on the one drive as well. I've left the drives out at the moment mainly to simplfy what is in the machine slightly, but I could pop em back in if you think it would be better.

Chuck(G)
June 30th, 2012, 02:59 PM
Given that you have an out-of-sync display with random garbage on it and you didn't mention the floppies being accessed, I'd start with the CPU section first.

Do you own a logic probe or oscilloscope so that you're able to see pulsing signals?

ChrisCwmbran
June 30th, 2012, 03:01 PM
I have a dual channel oscilloscope. I'm fairly new to using it but I've been reading up and watching lots of youtube vids on how to use them.

What do you need me to do?

Do you want me to install and connect the floppies so we can see if they are accessed?

MikeS
June 30th, 2012, 03:02 PM
Definitely something wrong in the video section; those dots and lines on either side of the main display should be a big clue but I'm just heading out for a few days' holiday.

Save me looking for it: where are the schematics for your particular board to be found?

MikeS
June 30th, 2012, 03:05 PM
Given that you have an out-of-sync display with random garbage on it and you didn't mention the floppies being accessed, I'd start with the CPU section first.Always hard to tell from a camera shot, but it doesn't really look out of sync, nor is it completely random; those artifacts on either side look like they should tell us something though.

ChrisCwmbran
June 30th, 2012, 03:06 PM
http://www.bitsavers.org/pdf/kaypro/1484-D_KayproTechnicalManual_Dec84.pdf

Pages 6-6.1, 6-6.2 and 6-6.3 by the looks of it!

The best I was able to capture is:


http://www.youtube.com/watch?v=Ot9EhEfPxBw

MikeS
June 30th, 2012, 03:26 PM
It looks like some parts of the display are pretty constant?

What you could try is swap some of the chips on P 6.3 with one of the other chips of the same type; if they're both OK then nothing should change, but if one has a problem then it should create different symptoms when it's in a different location.

ChrisCwmbran
July 1st, 2012, 01:55 AM
Thanks Mike. I'll try that. Enjoy your holidays! Hope you are going somewhere nice!

Chuck, what were you thinking about using the scope for tests?

Chuck(G)
July 1st, 2012, 06:27 AM
Could be something as simple as a bad ROM at this point if the display's not rolling (it's hard to tell, what with a video of a CRT display).

ChrisCwmbran
July 1st, 2012, 07:08 AM
As you say it is hard to tell, but I've just been looking at it with Dad.

We think it is rolling but not in (Ugghhh this is hard to express) a image is unstable on the screen type way, but almost as if the text on the screen is cycling down a row every time it blinks, at least in some areas of the screen.

I may have just found a major problem though - which isn't going to help at all.

In one of my earlier postings I commented that in one row of chips all the chips have corroded pins where none of the other chips around them have any pin corrosion at all. I just decided to very very carefully remove one of those chips:

952195229523

Other than the eight RAM chips, and very very slight corrosion on a few pins on the two Z80 PIO chips, all the other chips are perfect.

Why would the RAM chip legs corrode like this?

Where can I buy replacement chips?

Chuck(G)
July 1st, 2012, 07:30 AM
Just about any 64Kx1 (e.g. 4164) DRAM will work here--the Mostek's aren't special. On eBay.co.uk, there are several sellers of KM4164 chips for not much money.

ChrisCwmbran
July 1st, 2012, 07:34 AM
Why would the 8 RAM chips rust when none of the others have?

Incidentally is it a useful test to power the machine on with none of these RAM chips in situe?

Chuck(G)
July 1st, 2012, 08:27 AM
Why would the 8 RAM chips rust when none of the others have?

Incidentally is it a useful test to power the machine on with none of these RAM chips in situe?

Well, how many other Mostek chips do you see on the board? Manufacturers have their proprietary plating processes for IC leadframes. Could have been a bad lot or just characteristic of that vendor's chips.

You can try the CPU without memory, but the results probably won't tell you anything.

ChrisCwmbran
July 1st, 2012, 08:46 AM
Ok good point. The two Z80 PIO chips are made by Mostek and their pins are quite bad too.

Is http://uk.farnell.com/zilog/z84c2006peg/ic-pio-z80-6mhz-84c20-dip40/dp/1081865?CMP=KNC-GUK-FUK-GEN-KWL#relatedProducts a suitable replacement for them? I ask because these are 6mhz units....

The Z80 PIO isnt a Mostek chip however its pins are a little corroded:

95279528

The pins do however feel strong as normal. Is there something I can do to stop these getting worse or should I just replace it anyway?

You are right though! None of the other chips in the machine are Mostek! Did they make the legs of their chips from cheese? :P

Chuck(G)
July 1st, 2012, 09:04 AM
Is there anything you can do? I don't know--perhaps tin the tarnished legs with some solder, but be sure to clean up with alcohol after you're finished to get rid of any residual flux. The Chinese IC pull sellers seem to do that a lot. The danger of course, is that you'll compromise the seal between the leadframe and package,so be prepared to replace an IC if you mess up. Fortunately, Z80-family parts aren't hard to find.

That Farnell part should work fine, although, crikey, the price is pretty high! I can remember when Z80 CPUs sold for about USD$0.75 each in quantity.

ChrisCwmbran
July 1st, 2012, 09:12 AM
I see far more variation in prices on the 4164s! I get the impression that perhaps Samsung still make them - some overseas suppliers seem to have tens of thousands in stock (according to the web) and charge as low as about 1 each. On ebay they seem to be on average 3 or 4 each.

Other than Ebay I havent managed to find a UK supplier who seems to have new stock other than a few odd obsolete equipment suppliers who say they have 100s in stock but don't tell you how much they are. The only other time I tried to use one of these companies I couldnt get them to respond to any emails at all.

Is the Km4164 or equivalent still actually made? I presume across the globe people are still using them in some quantities even if its not massive.

With the corroded legs do you think a little bit of Loctite 7503 might work? http://tds.loctite.com/tds5/docs/7503-EN.PDF

Chuck(G)
July 1st, 2012, 09:26 AM
64K DRAMs were used in lots of equipment (even the later 5150 and 5160), so there are many equivalents and they should still be as plentiful as cockroaches. I doubt that Samsung still makes them, however--but the Koreans (e.g. Hyundai) made a lot of DRAM. Part numbers will vary somewhat--for instance, Hitachi uses HM4164; this reference should help (http://www.multigame.com/DRAMs_low.html).

Putting that Loctite on will likely create more problems than it solves. The last thing in the world that you should want is an insulating coating on contacts. You might try some Caig Deoxit (http://store.caig.com/s.nl/sc.2/category.188/.f), which serves not only as a contact cleaner, but offers a bit of protection.

ChrisCwmbran
July 1st, 2012, 09:36 AM
Am I right in thinking that this is a suitable replacement for the RAM?

http://www.ebay.co.uk/itm/HM4864P-2-65536-x-1-Bit-DRAM-150Ns-DIP-16-x5pcs-/300722522569?pt=UK_BOI_Electrical_Components_Suppl ies_ET&hash=item46047589c9

If its the same as is used in PCs etc too I'll order a good few so I have stock :)

Sorry to keep asking questions :) I hope Im taking in all your answers :)

Chuck(G)
July 1st, 2012, 09:52 AM
Those should work just fine.

ChrisCwmbran
July 6th, 2012, 08:31 AM
Ok, I've fitted the two new Z80PIO chips, and the new RAM chips.

Decided since I was awaiting further ideas as to what to try that I'd get some info on the vertical and horizontal sync for the monitor with my scope.

Scope videos included in following posts (Sorry about this).

I've now reseated all the chips referenced on 6-6.3 (CRT Control), and all the logic gate chips (arrays?) too. Where possible, if there were a pair of identical chips I swapped them over, but no swap caused a drastic change, however now the screen has changed somewhat. I don't know if its for the better or the worse.

Latest screen shot:


http://youtu.be/PjLhCEMiziw

I guess I'm back needed suggestions/advice?

ChrisCwmbran
July 6th, 2012, 08:33 AM
One of the two vertical sync shots:


http://youtu.be/94lfqi41bxI

ChrisCwmbran
July 6th, 2012, 08:33 AM
The other:


http://youtu.be/3Px50GIBs-A

ChrisCwmbran
July 6th, 2012, 08:34 AM
Horizontal:


http://youtu.be/UcfoTCPeliI

ChrisCwmbran
July 6th, 2012, 08:35 AM
http://youtu.be/u9ZtDHHOFpc

ChrisCwmbran
July 6th, 2012, 08:36 AM
http://youtu.be/wCb27RLrPs4

ChrisCwmbran
July 6th, 2012, 08:36 AM
http://youtu.be/YwWwkjo0OXA

ChrisCwmbran
July 7th, 2012, 09:22 AM
Do these videos yield any information about where I should be looking now?

I'm open to ideas what I should be trying now?

nige the hippy
July 11th, 2012, 10:57 AM
Hairy!

Which accounts for 50% of why it's gone quiet.

The video section is a bog standard arrangement with counters to provide timing, a 2716 eprom to generate the characters, and 2k of ram to store the ascii text, and a quick swap of the 2114s if they're socketed might be a worthwhile thing.........

......however the way the video is flashing would seem to indicate that the CPU is just sending crap to the video section. I suspect problems with 1) ram 2) rom 3) cpu 4) decoding logic in about that order.
Not knowing the way a kaypro initialises, I don't know whether it needs ram to clear the video.

so 1) have you checked the RAM is ok?

More thoughts later

ChrisCwmbran
July 11th, 2012, 11:42 AM
The main RAM is new.

The 2114s are socketed. I don't have replacement chips but we have tried swapping them in pairs.

Chuck(G)
July 11th, 2012, 12:20 PM
Here I come with stupid questions, again.

Have you verified the contents of the EPROMs? If one or more is garbage, then the CPU is just running around executing garbage, which would certainly give you that kind of display.

ChrisCwmbran
July 11th, 2012, 12:42 PM
Please ask me as many questions as you want!

Personally I don't have a means to check the EPROMS. If someone is able to burn new ROMs for it, I'd gladly pay them.

Please note Chuck we sadly have an additional problem as I mentioned in a PM to Nigel - last Friday a friend who was visiting knocked the machine which was stood up on end over, and on a quick test since then the display has vanished. There's no sign of physical damage at all - but as Im sure you can guess I'm worried he may have damaged the tube. Clearly I need further information on this. I'm going to do my bench tests again to prove the PSU board with load works, and that the PSU board works with the motherboard as a load as it did before. Either way I cannot see a visible problem with the tube, and there are no visible unseated chips, or damage to the boards.

MikeS
July 11th, 2012, 01:08 PM
Tell your friend that it was working fine before he knocked it over and he owes you a new one ;-)

All the connectors solidly plugged in (especially CRT socket)? Getting power to the monitor? Filament lit?

Check those sync signals again to see if they're still there and getting to the display board.

ChrisCwmbran
July 11th, 2012, 01:13 PM
Tell your friend that it was working fine before he knocked it over and he owes you a new one ;-)

Sadly he's the type who would be upset and insist on replacing the machine - and the last one I saw for sale was for $2000!



All the connectors solidly plugged in (especially CRT socket)? Getting power to the monitor? Filament lit?

Check those sync signals again to see if they're still there and getting to the display board.

I will do those tests in the morning. Are those tests I did with the scope actually yeilding positive and correct results?

Chuck(G)
July 11th, 2012, 01:32 PM
Do you own a composite or RGB monitor that's not VGA (e.g. CGA; it doesn't matter what system it goes to)?

ChrisCwmbran
July 11th, 2012, 02:05 PM
I have many monitors ranging from IBM 5151s, through stuff like Cm8833s but since coming out of storage I've not tested any yet. I have LCD monitors with composite video inputs too via phono jacks - had the Apple IIc hooked up to one of them the other day.

ChrisCwmbran
July 12th, 2012, 03:47 AM
Reading the values on J1 today:

Pin 1 - 4.440v peak to peak. Frequency appears to be 15.62khz. Value appears to be between -1v and +3v approximately.

Pin 2 - Doesnt exist

Pin 3 - 4.1v peak to peak. Possibly a signal at 2mhz??

Pin 4 - 5.25 volts peak to peak. 60.24hz frequency

These figures appear to be pretty much as they were before looking at the previous videos. The readings were taken with the video, power supply and logic boards all fitted and connected in the case with the exception of J1 (the video output of the logic board) where the readings were taken.

Nothing was displayed on the front of the tube - tried playing with the brightness control to no effect. There is a dim glow at the gun end of the CRT.

Checked the voltages where power is supplied to the motherboard too, and these are exactly as before.

MikeS
July 12th, 2012, 07:25 AM
Looks roughly like the right signals, so it looks like it's the display; probably not the CRT though if it's still glowing. Try moving the brightness control (and others) a bit back and forth; sometimes they get dirty and have bad spots.

Don't suppose you've found a schematic for the display board anywhere? Which make/model is it?

ChrisCwmbran
July 12th, 2012, 07:49 AM
I'll try that in a few minutes. The Video board is the Elston variety. Others could apparently be a Dotronix or a Toshiba. I can't find schematics for any of the three sadly.

The controls on the Elston board are Brightness, Vertical Size, Vertical Hold, Video Centering, Width, Focus and V Lin.

Do you want me to try all of those controls?

I guess I could try to take photos of the display board if that is any help?

Chuck(G)
July 12th, 2012, 07:55 AM
Most monitor PCBs are single-sided affairs and because they tend to mount fairly bulky components, are subject to solder joint failures and trace cracking. I would get my iron out and go over every single joint on the board, adding solder where appropriate and being on the lookout for cracks in traces.

In my experience, this can solve monitor issues at least half the time.

ChrisCwmbran
July 12th, 2012, 08:26 AM
Moving the little potentiometers back and forward doesn't seem to have changed anything. There's no sign of any brightness at all on the screen irrespective of any adjustment. My Dad, an ex-patent examiner is asking whether that suggests that perhaps the high voltage section of monitor isn't working. Is there a test we can do for this?

My multimeter (http://www.uni-trend.com/ut70d.html) appears to be able to measure upto 1000v.

Once the charge in the cards has had time to drop, I'll remove the boards, and examine the underside of the video board, which as you say appears to be a single sided board, and use the soldering iron to heat each joint. Out of interest, what temperature should I set the iron to for this task?

Chuck(G)
July 12th, 2012, 08:33 AM
Whatever works--I usually use 700F (about 350C) tips for that task.

MikeS
July 12th, 2012, 08:35 AM
As Chuck says, the weight of the components can crack the board or break a connection; check particularly around the flyback transformer connections and any large electrolytic caps.

If you have one of those neon bulb voltage testers or screwdrivers that they usually sell at the dollar (pound?) stores, they'll usually light if you bring them close to the high-voltage lead to the CRT; if the HV is working, the electric charge will also usually attract a piece of paper to the front of the screen. Of course the usual test is to remove the anode cap shortly after shutting down and grounding it to the CRT grounding strap or frame. Not a place for your multimeter probes...

ChrisCwmbran
July 12th, 2012, 08:46 AM
Ok thank you both for your help so far! It is very much appreciated.

I'll go over the board with a fine toothcomb (metaphorically!) and do the joints as suggested. I'll probably wait until the morning until I have good daylight to do this.

ChrisCwmbran
July 19th, 2012, 12:48 PM
Sorry about the delays. Ive been run off my feet with work.

We've spent ages now checking the continuity of all the tracks on the video board continuity and they are fine. There are a few points where the board has obviously been scratched before, presumably many years ago, and the areas of copper that were made bare seem to have been covered in solder. There is also a date and an intial written on the board presumably detailing this repair. All the solder joints look ok visually. None of the components seem at all loose or have any undue wiggle to them.

In the morning I'll begin the resoldering process.

ChrisCwmbran
July 20th, 2012, 05:27 AM
Just out of interest, I know this might be an odd question. I have a:

http://www.pcb-soldering.co.uk/aoyue-998-smd-rework-station-hands-free-cpu-controlled.html

Would using its hot air gun to warm the joints be a viable alternative? I have no problem with using the soldering iron - it just occured to me that this is another thing that might work?

Chuck(G)
July 20th, 2012, 07:23 AM
I'd stick with the iron because solder can be added to each joint as needed. Leave the hot air approach to SMT work.

ChrisCwmbran
July 20th, 2012, 07:54 AM
Where you asked about other monitors, I have a Sanyo DM2112 green screen composite monitor. Is there any way to connect the outputs of the video connector on the logic board to this to check that's output is still good?

Chuck(G)
July 20th, 2012, 08:32 AM
Maybe. I'll have to look at the Kaypro schematics.