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tezza
February 21st, 2009, 11:38 AM
I've got a Redstone clone Apple II+. It's the least valuable of all my Apples but it's useful as a test machine, rather than using the more valuable units.

Anyway, it's developed this problem. It seems to boot fine when cold but after a minute or two, the keyboard stops working and the screen usually freezes. Switching it off and on again usually just causes a hang (white screen with a few diffuse patterns).

Obviously something is warming up and becoming faulty. I don't think it's the ICs as I've done a full substitution and with no improvement Any ideas?

Anyone come across this before? Sockets? Power supply?

Tez

wmmullaney
February 21st, 2009, 12:00 PM
I'd take a peek inside the psu or replace it if you have another.

tezza
February 21st, 2009, 01:53 PM
Yea, the PSU was a suspect but I've swapped that with a good one and no, it's fine. I've also swapped the keyboard to eliminate that aspect. The problem is definitely in or on the board somewhere.

Solder points LOOK ok, but I guess that can be fairly subjective. I've inspected the sockets. Again, they LOOK ok but remember these were soak in mouse pee for years so who knows.

Incidently, I'd kept a spare circuit board from the Apple haul last year. Visually it LOOKED ok, so I populated that with the ICs from the Redstone with a view to using this board if everything started working.

Well, after cooking a couple of RAM chips (yes, I did have them the right way around) I decided this board is in even WORSE shape than the existing one!

Druid is right, a shorted RAM chip can take the first layer of skin off a finger..lol

Tez

mfortuna
February 23rd, 2009, 03:32 AM
I don't think crystals are usually heat sensistive but you could be losing the clock. Sockets and etch can cause problems due to thermal effects. Since it remains dead once it warms up you could try finding the suspect component with freeze-spray (tech in a can). Spray the components one at a time and power cycle the system to see if the chilled component has made a difference.

Mike

channelmaniac
February 23rd, 2009, 06:02 AM
If it were the crystal then you'd see a loss of sync on the monitor and the display would go batshit. There's only 1 crystal on the system and it controls the timing for everything.

Now, it could be a problem in the clock dividers further down the line but that's very unusual.

My money is on a bad RAM chip, ROM, or CPU. Try swapping the whole first RAM bank with the 2nd RAM bank and see if the system suddenly becomes stable. If it does then you have a bad RAM chip.

Next swap the CPU and see what it does.

If it's a bad socket then you should be able to make it lock up at will by tapping on the board in different places.

tezza
February 23rd, 2009, 11:06 AM
Hmm..the crystal. I hadn't thought of that. I'll have to check the reference manual and find out exactly where the crystal is?

>the display would go batshit

Not sure what you mean by that. The display is a white square with very diffuse repeating patterns in it. It's not your classic "garbage" screen as such. I'll have to post a photo.

>My money is on a bad RAM chip, ROM, or CPU.
>Try swapping the whole first RAM bank with the 2nd
>RAM bank and see if the system suddenly becomes stable.
>If it does then you have a bad RAM chip.

>Next swap the CPU and see what it does.

My money was on this too initially. However, I've done a complete IC swap (including CPU and ROM) with a working machine and it's made no difference?

>If it's a bad socket then you should be able to make it lock up at will by >tapping on the board in different places.

Yes, that's what I thought too. However, tapping makes no difference at all. Not in the slightest.

The machine always starts up ok when stone cold. The keyboard often works for a second or two then stops. The cursor still sits there blinking. It's only when you turn it off and turn it on again that the white screen appears. It then doesnt boot.

One time after I'd switched the machine on and off (it had only been on for a minute or so) it hung for about 5 seconds, then THEN booted. It was almost like it was on the cusp of not progressing with the boot.

>Since it remains dead once it warms up you could try finding the suspect component with freeze-spray (tech in a can).

Yes, sounds like this would be a good thing to try. I've been hoping I could ID the problem without resorting to this, because the unit is probably worth less than the can of freeze-spray I'd have to buy...lol

Tez

scommstech
February 23rd, 2009, 02:07 PM
Sounds like you may have IC socket problems or track problems since youve
changed the obvious.
I had a board like this. Chips, PSU, keyboard, all ok. Turned out to be a
combination of weak socket springs, and bad track. Only realised the sockets
where bad when swapping the ICs some of the socket spring connectors fell
out. Tapping was not enough to trigger the fault. Slight flexing of the board
showed up the track problems.
Some of the clones where made on the cheap and the quality is not
consistant. Best of luck.
Scommstech

tezza
February 23rd, 2009, 02:26 PM
Some of the clones where made on the cheap and the quality is not
consistant.


Yes, and circuitboard quality is not enhanced by being home to generations of mice for 15 years.

I did scrutinise the board with magnifying glass to see if I could see any track faults. Looked ok. Bending the board whilst the machine was on didn't show up anything.

There is a good chance something is wrong deep in a socket somewhere.

Trouble with me is these things become a personal challenge and I spent WAY too much time and effort on diagnosing them/fixing them. I mean..I've got 2 other working Apple II+s and 2 Apple IIes already! Why not just keep this for parts?

It just annoys the hell out of me when I have a complete unit that is not going and don't know WHY!

I guess I'll have to learn to move on :)



Best of luck.
Scommstech


Thanks. I think I'll need it

Tez

scommstech
February 23rd, 2009, 04:14 PM
If youve got a scope, can you compare one of youre good motherboards to the faulty one. Be a shame to use it for spares .
Regards
Scommstech

pavery
February 23rd, 2009, 05:12 PM
Hey Tezza

You say
However, I've done a complete IC swap (including CPU and ROM) with a working machine and it's made no difference?


Does this mean you swapped all the ICs, then on test the fault was still the same? I.e. With *all* different ICs, the fault is still the same?

Philip

tezza
February 23rd, 2009, 05:20 PM
Hi Philip, that is correct.

I replaced the whole set of ICs with ICs from a working unit. The ICs from the non-working unit I put in the working unit.

The working unit still worked, and the non-working unit still didn't work.

It doesn't appear to be the ICs.

A dogey socket seems to be the prime candidate. I've wriggeled all the sockets thought and seated/reseated ICs in parts of the circuit I feel might lie the problem. No difference. I've also inspected all sockets with a magnifying glass. I did find one or two bent clips but these seem to hold the IC legs firm when the ICs are inserted. They are certainly contacting the legs. With this clips I checked to make sure there is a closed circuit through to the bottom of the motherboard (while the board was still warm). There is.

I think I might need to buy that can of freeze spray after all.

Tez

channelmaniac
February 24th, 2009, 08:22 AM
If the crystal was bad, you'd lose sync and the display would be unreadable.

Since you have a good sync lock on the display I'd think the crystal itself would be good.

RJ

scommstech
February 24th, 2009, 08:27 AM
I think I might need to buy that can of freeze spray after all.

Tez[/QUOTE]

If the spray doesn't show up the prob, you may want to consider running a
soldering iron over the board's solder joints.
These old clone boards can suffer from dry joints.
Its better to remove the ICs from the area being treated but Ive left them in
and got away with it.
Regards.

Druid6900
February 24th, 2009, 10:57 AM
It's not just the cheap clones that suffer from "socket sag". The Apple III was famous for intermittents and having to spend a couple of hours resoldering all the connections on them to get the pile of crap going again.

I've never had any problems with leaving the chips in while reflowing al the sockets on a board.

mwillegal
February 26th, 2009, 04:20 AM
If you are so challenged with trying to solve these riddles, you really should invest a bit in some test gear (an oscilloscope, for starters). It will make the process much more enjoyable and productive. I managed to find and spruce up a 100MHZ Tektronix 465 for a total cost of $130, so it doesn't need to cost an arm and a leg.

The down side is that, once you get up to speed, we will not get to share the process with you, because you will probably be able to solve the vast majority of the problems without assistance.

Regards,
Mike Willegal


Yes, and circuitboard quality is not enhanced by being home to generations of mice for 15 years.

I did scrutinise the board with magnifying glass to see if I could see any track faults. Looked ok. Bending the board whilst the machine was on didn't show up anything.

There is a good chance something is wrong deep in a socket somewhere.

Trouble with me is these things become a personal challenge and I spent WAY too much time and effort on diagnosing them/fixing them. I mean..I've got 2 other working Apple II+s and 2 Apple IIes already! Why not just keep this for parts?

It just annoys the hell out of me when I have a complete unit that is not going and don't know WHY!

I guess I'll have to learn to move on :)



Thanks. I think I'll need it

Tez

tezza
February 26th, 2009, 02:42 PM
If you are so challenged with trying to solve these riddles, you really should invest a bit in some test gear (an oscilloscope, for starters). It will make the process much more enjoyable and productive. I managed to find and spruce up a 100MHZ Tektronix 465 for a total cost of $130, so it doesn't need to cost an arm and a leg.

Yea, well. I have thought about this from time to time and I'm sure your right. I'm still a way from knowing the basics in order to use one though, and I'm not sure how common older ones are here. I should put a seach into our local auction site and see if one appears.

I've been holding off getting any test equipment (apart from a multimeter) as


I'm only collecting a limited number of machines and..
My primary interest was never intended to be playing around with the hardware. It was mainly for display/historical purposes.


So I didn't want to buy test stuff (and learn to use it) for a one-off. However, the more I get into this hobby the more I've been FORCED to tinker with the hardware. And actually I've enjoyed it. Also, I've realised that even with a limited number of machines, they do need fixing from time to time (they are old and cantakerous in the main). And mostly I (with some help from friends now and again) am the only one who CAN fix them. There is no repair facility anywhere.

So yes, some investment in test equipment (and learning how to use it) is probably worthwhile. It might have to wait until I get through this recession first though, unless I can pick an oscilloscope REAL cheap!

Tez

channelmaniac
February 27th, 2009, 05:26 AM
Yeah,

I know what you mean about the recession. This has been a hell week. We went through a re-org at work and I've been scrambling. Several friends are gone and I survived.

They put me on a different team. I don't have access to systems, email aliases, and data yet and I'm not sure who my immediate supervisor is yet.

URG.

But, hey, I have a job. Plus the position they put me in could be considered a plum!

tezza
March 25th, 2009, 06:25 PM
I'm on a roll!

After fixing the TEAC disk drives (http://classic-computers.org.nz/blog/2009-03-23-teac-apple-disk-drive-repairs.htm), I returned to this problem with my Apple II+ clone.

On investigation with the scope, I found the RESET line on the CPU was being held low. This halts the processor of course. No wonder nothing seemed to be working!

This line only went to three things, the expansions slots (which were empty), the keyboard (which was unplugged) and the power up generator (a 555 IC).

I checked out the 555, and found that, rather than just sending a pulse at startup, the the timer was holding this line high, (thereby bringing the RESET line low). I traced the fault to a faulty capacitor in the associated circuitry.

Capacitor replaced and the machine is back to full working condition!

As usual, I've written a detailed account (http://classic-computers.org.nz/blog/2009-03-29-re-repairing-an-apple-II-plus-clone.htm), for my own records and those who might want to read it.

Thanks for all your suggestions in this thread.

Tez

Terry Yager
March 25th, 2009, 09:15 PM
Damn, you write good, tez. Ever considered a new career in technical writing? OTOH, techies are so accustomed to de-cyphering manuals by now, they prolly wouldn't understand one written in prain Engrish...their brains would automatically garble it.

--T

tezza
March 25th, 2009, 11:50 PM
Thank you Terry.

These blogs are kind of a diary to myself so I know what I've done with my collection, but I also hope they will inspire causal googlers and whoever else reads them to have fun with these old machines. Perhaps even to join in these forums.

Orginally when I started collecting my list of computers in late 2007, I was just going to stockpile them for a retirement hobby 15 years or so down the track.

It hasn't quite worked out that way.... :)

Tez

cosam
March 26th, 2009, 12:49 AM
I checked out the 555, and found that, rather than just sending a pulse at startup, the the timer was holding this line high, (thereby bringing the RESET line low). I traced the fault to a faulty capacitor in the associated circuitry.

Capacitor replaced and the machine is back to full working condition!
Steady on, Tez - at this rate you'll have nothing left to fix and be left wondering what to do with yourself! ;-) Nice work, you're really getting the hang of this now.

tezza
March 26th, 2009, 01:24 AM
Steady on, Tez - at this rate you'll have nothing left to fix and be left wondering what to do with yourself! ;-) .

Is there ever nothing left to fix when you have vintage computers? :)


Nice work, you're really getting the hang of this now.

Thanks. Yes it's starting to gel. I can feel that CP/M N8VEM project getting ever closer..lol

Tez

Terry Yager
March 26th, 2009, 01:32 AM
I can feel that CP/M N8VEM project getting ever closer..lol

Tez

Jump in, d00d! I'm half as smart as you, and I'm working on it...how hard can it be? All the work has been done already, if ya have the time to read up on it all.

--T

mwillegal
March 26th, 2009, 05:06 PM
Steady on, Tez - at this rate you'll have nothing left to fix and be left wondering what to do with yourself! ;-) Nice work, you're really getting the hang of this now.

I have a board that I expect would keep him busy for months! New intermittent failures a week or two after each repair it's had.

Regards,
Mike Willegal

Terry Yager
March 26th, 2009, 09:12 PM
I hate intermittent faults! Every time ya go to fix it, it ain't broke...Gaaarrr!!!

--T