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tezza
February 24th, 2008, 01:46 AM
I’ve been having fun(?) with baby Macs this weekend.

First I was given a Mac SE on Friday. Case is in good condition but the screen was initially just vertical wavy lines and (after a few on/offs) it didn’t go at all. I pulled it apart and resoldered connections as advised in a few diagnostic guides off the Internet but to no avail. I’ve put it to one side for now. I’m not sure if I can be bothered to replace the suspected faulty caps or diodes just at this point in time. It’s hard to work on as it’s so grimy inside! Is this typical of Macs? It is fairly vintage, so I may have a go later on when I feel more motivated. Or I might just sell it as a broken unit.

Are SE’s significant from an historical or collectable point of view?

Second, I did some work on my other Mac, the Classic II. This is an ex-school machine with a copy of “At Ease”, a security program to stop little hackers dabbling with the System. This is fine, except when the admin password had been lost, in which case it is a pain in the arse because you can't actually DO anything!

Anyway, I had what I thought was a good 2-disk copy of System 7.1 so I reformatted the hard drive and re-installed the DOS. Problem was, the 2nd disk turned out to be faulty, giving me an unknown error -#192 before completing the install. I found I could only install a minimal version of the DOS, not the full one (grrr).

I found a copy of 7.1 on the Internet in .sea.hqx format. Anyone know how I can turn this into 1.4MB Mac install floppies from a PC? I’m picking it won’t be easy.

I also tried to install Lemmings on this machine. I had the disk but the installation insists you find pieces of info in the Lemmings Manual to install properly. I had no manual of course. Anyone know where I might find a Mac-version manual on the Web (I have looked but no luck).? Alternatively, a cracked Mac version where no such manual info is required?

Hmm..when I look back on what I’ve written, not a terribly successful weekend vintage-computer wise.

The baby Macs are kinda cute though!

Yzzerdd
February 24th, 2008, 09:02 AM
I've got a dead SE too. It is second priority on my imaginary "to fix" list. Only reason is because I have a crapload of stuff for it, including original manuals, and the rare-to-find original book packet that came with it, with a different disk on every page. Want a pic of it? It is pretty cool, and has all the disks with it.

I think with that format, you need a mid-90s power mac, or an LC. A Macintosh II could do it as well. But hey, I will be nice. I've got "Disk 2" here at the house. I wanted to do a fresh install on my Classic II, but I am missing one of the disks, the "tidbits" one. If you make a copy of your tidbits disk, I will do the same with my "Disk 2." Then we can send them to eachother. The ProDos 1.1 disk I sent awhile back seems to have survived the mail alright, so I'm sure these 3.5" disks will too, without a special envelope. I've also got System 7.5 update 2.0 here at the house, and I could make copies of that too. You have to have system 7.5 installed to begin with, which I didn't know when I got them. My Classic II is a school machine, too! My SE is second owner, though, me being the second. Do you know if that PSU is good in your SE?

--Ryan

Anonymous Freak
February 24th, 2008, 09:26 AM
The SE was one of the major turning points in the Mac, as it was (along with the simultaneously-released Macintosh II,) the first Mac to have a built-in hard drive. That said, they are *VERY* common, and not worth very much unless they are mint with all original packaging. A standalone one that is in decent working shape, but with no packaging is worth maybe $10-$20. (In other words, not worth paying for shipping.)

You can bypass At Ease by just holding down shift on boot. That is the equivalent of 'safe mode' on Windows. Another option would be to boot from your system floppy that works, and just remove the At Ease control panel and extension from their respective folders on the hard drive.

tezza
February 24th, 2008, 04:34 PM
I've got "Disk 2" here at the house. I wanted to do a fresh install on my Classic II, but I am missing one of the disks, the "tidbits" one. If you make a copy of your tidbits disk, I will do the same with my "Disk 2." Then we can send them to each other.

Done! I'll PM you about this.


Do you know if that PSU is good in your SE?

No absolutely sure but the hard drive spins up and seems to boot. I can't see what it does of course.

tezza
February 24th, 2008, 04:37 PM
You can bypass At Ease by just holding down shift on boot. That is the equivalent of 'safe mode' on Windows. Another option would be to boot from your system floppy that works, and just remove the At Ease control panel and extension from their respective folders on the hard drive.

Yea, I had tried both those options. Whoever installed it had covered both those bases...it just kept reverting to the admin screen and asking for a password.

Anyway, it's gone now. A reformat nuked it. I just need to get a full System 7.1 on the Classic II now.

Druid6900
February 24th, 2008, 08:50 PM
I had a SE, (HD, Superdrive, mem maxxed out) but, it worked, so, I didn't bother to open it up before selling it on FleaBay for (drum roll please) $27US. Cost more to ship it to Texas.

Now, if it's like the 128 and the Plus, etc., the video card is mounted vertically, letting the flyback hang out there in space.

Try removing the solder and re-soldering all the pins on the flyback (I'd do it one at a time or the flyback falls down into the bottom of the case LOL) and see if that solves the video problem. There may also be a cement power resistor on the board, do the same thing to that.

I don't know how many horizontally mounted flybacks I've had to do that to, but, it was a quick, simple and profitable repair revenue stream.

Tony, if the flyback in the Osbourne is horizontally mounted (it's been a long time since I've been in one), that may be your problem too.

The weight of the flyback, going through the heating and cooling cycle of use, eventually and inevitably, cracks some solder joints.

Sharkonwheels
February 24th, 2008, 09:06 PM
The flyback is the deal with the cable, and a suction cup-looking thingie, stucj to the backside of the CRT, right? On mine, it's mounted inside a cradle holding it up, the coil-looking piece on the other end of the suction-cup ;)

Dang technical, ain't I? "Suction-cup-looking-thingie"

hehehe....


T

Druid6900
February 24th, 2008, 09:14 PM
Umm, yeah, ok.

Yes, I believe you have the right piece of equipment located. The bracket is usually just attached to the board with a twisted tab and will do nicely for the "life" of the unit, but, the stuff we're talking about is in it's second "afterlife".

Even if the frame is soldered to the board, it's joints can give up the ghost too.

Whenever I'm fixing a "no video" problem with a horizontally mounted flyback, resoldering the FB is the first thing I go for. I'd say, between 85 and 90% of the time, that was the problem.

YMMV

tezza
February 24th, 2008, 10:14 PM
INow, if it's like the 128 and the Plus, etc., the video card is mounted vertically, letting the flyback hang out there in space.

Try removing the solder and re-soldering all the pins on the flyback (I'd do it one at a time or the flyback falls down into the bottom of the case LOL) and see if that solves the video problem. There may also be a cement power resistor on the board, do the same thing to that.


Yea it does hang out there. Those pins were the first things I paid attention to. However, I didn't REMOVE the solder, I just melted it and let it reform. If it was the problem I figured that should that have done the trick ....or do I really need to remove all the solder and add some more?

tezza
February 25th, 2008, 01:51 AM
Ok, this SE is starting to glare at me from the "broken junk" corner of my hobby room. I should try to fix the thing...

This document I got off the web suggests it's a few dead components, but there is no sign of blasting, popping or damage whatsoever.

http://www.biwa.ne.jp/~shamada/fullmac/repairEng.html

The screen does not go at all. It's completely black. No raster. However, the first time I switched it on it WAS going with no image but wavy lines. Verticle ones I think, but there was an off-centre vertical on that was brighter than the rest. I

've tried reforming the solder on the flyback. I could replace all the components suggested in the documents but it's a big job. Is there anything I could do with a multimeter which would help isolate the fault?

Of course it could be the flyback itself. Any way to test this?

Druid6900
February 25th, 2008, 02:01 PM
Well, it's not so much a test for the flyback as it is for the presence of high voltage to the CRT, but, turn it on and run your hand over the screen. If you feel static, then you have high voltage, if you don't, you don't. Much better then sticking your tongue on the 2nd anode LOL

I've found that completely replacing the solder is best because it oxidizes over time and that oxidization flows to the "outside" of the solder when you just re-melt it. This is knowledge garnered from a 3 day "learning experience"

tezza
March 2nd, 2008, 01:41 AM
Well, after some more resoldering, testing, peeking, poking, looking and reading I've come to the conclusion it probably is the flyback transformer itself that's faulty in this little baby.

I'll tuck it away in my "broken.-will-fix-if-I-stumble-on-some-parts" corner of the room for now.

It's the only thing there at the moment but not for long if I keep carting free stuff home.

tezza
March 3rd, 2008, 01:20 AM
Ok, I just saw a Mac SE/30 at a buy-now price for $US16, working, with software. It's local so I can pick it up.

Couldn't resist it, so I guess the SE I've been poking around with will now just be a parts-machine forever, unless a Fly Transformer or a replacement analogue card somehow lands in my lap.

Yzzerdd
March 3rd, 2008, 05:42 AM
Make it into a MacQuarium! Be the only person down there to have one! Hehe. BTW: I got the disk you sent, thanks! I hope the one I sent gets in soon. Too bad it murdered my system...

--Ryan

kastegir
March 3rd, 2008, 10:21 AM
Ok, I just saw a Mac SE/30 at a buy-now price for $US16, working, with software. It's local so I can pick it up.

Nice! I need to dig mine out of my workshop/storage room and get it cleaned up and running again.

tezza
March 8th, 2008, 02:02 AM
I've picked up my Mac SE/30. Wow, blazing speed compared to my Mac Classic II!

A nice tidy little unit to add to my collection.

Hey guys can you take a look at the keyboard I got with it? Is this a standard "typical" keyboard released with the SE/30 or was it be the wider version with the cursor key cluster? (I've got one of those with the broken SE so if so, I'll just swap them).

Yzzerdd
March 8th, 2008, 07:14 AM
I may be mistaken, but I think that is the right keyboard. My Macintosh SE came with one, but on the other hand, my Classic II came with one like that as well. I just went to Everymac.com, and they seem to show the SE with that keyboard, as does Mactracker (http://mactracker.dreamhosters.com/), a program you may be interested in.

I envy your SE/30,

--Ryan

kastegir
March 8th, 2008, 09:07 AM
Hey guys can you take a look at the keyboard I got with it? Is this a standard "typical" keyboard released with the SE/30 or was it be the wider version with the cursor key cluster? (I've got one of those with the broken SE so if so, I'll just swap them).

I believe that keyboard is the ADB Keyboard II, which is a later version, release with the LC series.

tezza
March 8th, 2008, 12:28 PM
Thanks for that info. guys.

Ryan, my Classic II also came with the same keyboard that graced the SE/30. I guess it's indeed the one for the baby Macs.

I read on the web the SE/30s were sometimes used as servers. I can believe it. Its the fastest baby mac I've had the pleasure to handle. It has 6.1 installed so I guess the overheads are lower than the 7.1 on my Classic II....but it's mostly the faster processor I imagine.

Now I just need to figure out how to get the 6.1 installation disks off the Internet somehow. Time for some googling.

tezza
April 6th, 2009, 03:19 AM
Well, after some more resoldering, testing, peeking, poking, looking and reading I've come to the conclusion it probably is the flyback transformer itself that's faulty in this little baby.

I'll tuck it away in my "broken.-will-fix-if-I-stumble-on-some-parts" corner of the room for now.

It's the only thing there at the moment but not for long if I keep carting free stuff home.

Now that I've got more experience poking around hardware I had another look at this lonely "stored-in-a-corner" baby Mac tonight.

After testing many bits and pieces I've come to the same conclusion. The CTR isn't getting high voltage power. Transistors, diodes etc. seem ok though and I've rereshened the solder. No difference.

Probably flyback BUT I'd like to prove it wth a more systematic look. Does anyone know of a SE 30 technical manual on the web which contains a circuit diagram, at least of the analog card? I have the SE/30 manual but that's pretty basic and it doesn't show the circuitry.

Tez

arjoll
April 6th, 2009, 03:49 AM
If you're poking around the display be careful of the EHT (connection on the side of the CRT). A CRT acts like a capacitor, storing a charge for a surprising amount of time after switch-off. The EHT will be quite a few kV.

Touching it is unlikely to kill you (very low current) but give you a reasonable boot and a hell of a fright!

If you had some kind of display you've probably got EHT. My knowledge of TV circuitry is basic but I suspect you've got line drive as well, so your LOPT is probably ok.

Do you have any contacts in the TV service industry? If so it may be time to call in some favours :)

Also drop me a PM re the manual, there's a chance I may be able to help.

tezza
April 8th, 2009, 01:49 PM
Partially thanks to info. from a link arjoll sent me, I MIGHT have cracked this problem.

I'll find out when I replace the suspected faulty component tonight.

Tez

tezza
April 9th, 2009, 03:45 AM
Well, that didnít work.

Iíve come to a brick wall with this one. Before I consign the Mac SE back to the parts bin, is someone able to look at this circuit diagram and the associated text at the end of this message and see if there is anything else I should check?

The circuit is for a Mac Plus but (apparently) the SE uses the same horizontal circuit. Furthermore, the codes on the diagram donít refer to exactly the same components on the SE (The T1 Flyback is called T2 on my analogue board for example) but Iím sure I know what they are referring to.

Here are some facts.


The symptoms are a completely back screen. No raster. A faint light does appear in the neck though.

I have a working Mac SE/30 which Iíve used as a standard to make comparisons. It has the same type of analogue board.


I suspected either the flyback transformer (T1), C3, CR1 or Q3.


Voltages on T1 pins 1-4 on the Mac SE are found 12v
Voltages on T1 pins 1-4 on the working SE/30 are 20v!
Voltages on T1 pins 5-8 on the Mac SE are practically zero. No high voltages (hence a back screen)
Voltages on T1 pins 5-8 on the working SE/30 are as indicated on the diagram (i.e. very high!)

In the description of the circuit it says ..Ēand C3/CR1 generated a boosted Vcc at pin T1 1-4Ē. I read that to mean that 12v is boosted to about 20v. Certainly on the working SE/30 there is 12v one side of the C3/CR1 and 20v to other. Given that in the broken SE there is NO boosted voltage, I figured maybe C3 was faulty and replaced it. No change. I then replaced the diode CR1 even though is seemed ok. Still no change!

Iím stuck.

I measured the resistance across the Q3 transistor and itís similar to the working one. It doesnít appear damaged. Iím not sure if this transistor would cause the problem anyway, would it?.

If it is not C3/CR1. why then is the voltage on the T1 input pins 1-4 12v and not 20v? What SHOULD boost this voltage up? I figure this lower voltage on pins 1-4 is why the flyback transformer is not firing high voltages out of the circuitry connected to 7 and 8?

Is the flyback itself the likely culprit? Would this be causing the low voltages on those pins (even though they seem to be input pins)?

Any comments most welcome. If it is the flyback transformer Iíll just keep the SE for parts. They are hard to get and expensive to replace. However, I just want to check if there is not some obvious easy-to-replace component that Iíve missed?

Thanks in advance.

The full PDF the digrams below are sourced from is at
http://home.earthlink.net/~gamba2/images/plus_analog.PDF

Tez

http://classic-computers.org.nz/blog/images/2009-04-09-mac-horz-circuit-text.jpg

http://classic-computers.org.nz/blog/images/2009-04-09-mac-horz-circuit.jpg

cosam
April 9th, 2009, 05:38 AM
Are the voltages at T2 the same on both machines?

nige the hippy
April 9th, 2009, 11:16 AM
I'd really be looking at Q3 (out of circuit) by now with a diode-test setting on my meter, sometimes they go short collector-emitter, sometimes short emitter-base, sometimes they just pop, and sometimes the legs fracture with differential expansion between the transistor & the heatsink, all of which will kill the EHT & 12V. measuring in-circuit won't give very conclusive results, as the transformer windings are low resistance.
I'm not sure if the BU406 has an internal diode pointing upwards between emitter & collector, so don't be surprised if you get a 0.6V reading with emitter positive to collector negative.

tezza
April 9th, 2009, 11:25 AM
Are the voltages at T2 the same on both machines?

I had a go at this before posting. Believe it or not it's quite hard to know. Main problem is knowing exactly WHERE the pins come out on the back of the circuit board. I can see where the transformer is positioned but at the other side of the board it's hard to know what pins are its pins and what pins belong to other components lol. Things are crammed up in there.

Anyway, I'll try again. Thanks

Tez

tezza
April 9th, 2009, 11:34 AM
I'd really be looking at Q3 (out of circuit) by now with a diode-test setting on my meter, sometimes they go short collector-emitter, sometimes short emitter-base, sometimes they just pop, and sometimes the legs fracture with differential expansion between the transistor & the heatsink, all of which will kill the EHT & 12V. measuring in-circuit won't give very conclusive results, as the transformer windings are low resistance.
I'm not sure if the BU406 has an internal diode pointing upwards between emitter & collector, so don't be surprised if you get a 0.6V reading with emitter positive to collector negative.

Hi Nige,

Yes, this one I checked out before posting too.

When you say out of circuit, do you mean with the power switched off, or desoldered?

I don't have a specific diode tested on my multimeter. However, I believe you can do this just using a continuity setting, yes? It seems to check out ok (I get readings similar to what I'd get on a diode between base and emmiter and base and collector i.e. no continuity one way and a small amount of resistance the other way) and whatsmore the reading are quite similar to the one on the working SE/30.

However, I'll check again just to make sure.

Tez

cosam
April 9th, 2009, 12:50 PM
Yep, out of circuit as in removed from the board. Otherwise the resistance through the components round about Q8 may throw your readings off.

If that doesn't reveal anything: Have you compared the signals on the other side of T2? Base and collector of Q6 would be good test points. If the pins are hard to reach, you might be able to latch onto other parts connected to them.

Unknown_K
April 9th, 2009, 01:54 PM
This page is helpful:

http://www.biwa.ne.jp/~shamada/fullmac/repairEng.html#BlackOut

tezza
April 9th, 2009, 02:54 PM
This page is helpful:

http://www.biwa.ne.jp/~shamada/fullmac/repairEng.html#BlackOut

Yep, thats the doc I started with. It points to the general area most likely at fault but as all components looked OK and tested ok as far as I could measure them, I wanted to islolate the exact one using a circuit diagram and testing equipment before I started to remove and replace things. I thought I'd found the culprit (the 220 capacitor on Pin 4 of the flyback) but...apparently not.

Incidently, for those that may be reading, the component identifiers in the web document posted by unknown_k are different than those in the circuit diagram I've pasted above. The diagram is for a Mac Plus (couldn't find one for the SE). The SE and SE/30 have the same horizontal sweep circuit but the components do not have the same identifiers.

Tez

arjoll
April 9th, 2009, 04:01 PM
The faint light is good, it means you've got CRT heaters.

I presume you have some signs of life around Q6? And if you turn the brightness up you get no blank raster?

I'd suspect Q3 as a possibility as well. They're around NZ$4 from Farnell so not an expensive part to try. Replacing all the electrolytic caps isn't silly and will only cost a couple of dollars.

Before that it might be worth testing the LOPT (flyback transformer). You'll need to discharge the filter caps and the tube (which acts like a big cap) through a high value resistor, then check here (http://www.repairfaq.org/sam/flytest.htm#flybas) for some basic tests.

I can run that circuit past a friend who is a electronics tech and has sorted out a Sord monitor (with no circuit!) for me, but with it being Easter it will be next week before I have an answer.

tezza
April 9th, 2009, 05:11 PM
I presume you have some signs of life around Q6? And if you turn the brightness up you get no blank raster?


Yes to both. Life around Q6 and there is no raster at all.

OK, some measurements. Codes refer to the circuit diagram, NOT the codes in the SE/30 repair web document (which are different)


Q3 emitter - 11v (Non-working SE), 20v (working SE)
Q3 Base/T2 pin 3 - 0.1v (Non-working SE), 0.7v (working SE)
T2 pin 2- 11.4v (Non-working SE), 8.9v (working SE)

(T2 pin 1 and emitter of Q6 very similar to the T2 pin 1 readings as you would expect)


Q6 base - 0.46v (Non-working SE), 0.39v (working SE)

The 20v and 11v on the T1 pins 1 to 4 seems a significant difference. Is it likely to be though? If so, would it be the solely the result of the Q3 transistor or is the voltage on that side of the transistor affected by other inputs to T1? As I understand it Q3 is a power transistor whose function is to pulse voltages on and off phase to get a horizonal sweep. Is this correct? If so, could I use a scope to test it?



I can run that circuit past a friend who is a electronics tech and has sorted out a Sord monitor (with no circuit!) for me, but with it being Easter it will be next week before I have an answer.

Thanks Andrew, but it's not worth bothering anyone about (except for the guys on here of course...we like that kind of thing :) ). This is really just a spare (I have another 3 baby macs already!). It's more of a challenge and a learning exercise more than anything else. I want to figure out exactly what it is and, if it is a cheap component, replace it. If it is not a cheap or easy to get component (i.e. the flyback) I'm not going to worry about it.

I do want to diagnose it though.

So, based on those voltages does Q3 still look likely? I'm sure extracting it won't be easy and I suspect it will be a destructive test (in that I might have to cut it out). Would a scope tell me anything?

Andrew, will Farnell ship single components like that and don't they have to import them (shipping charges?) I have a feeling the minimum order is $10.

Tez

tezza
April 9th, 2009, 07:43 PM
Ok, I removed the Q3 transistor very carefully so I could replace it if needed.

A transistor can be thought of as two diodes, between the base and collector and base and emitter, right?

A check on the base<--> emitter showed ok. About 500 ohms or so one way and infinite resistance when I swapped the probes.

A check on the base<---> collector showed infinite resistance BOTH ways! This is unusual, even for one of these power transistor right? I should have got a reading similar to the base/emitter check with the negative probe on the base and the positive probe on the collector, correct?

If it's yes to the above, then the problem is indeed Q3. All the evidence does point to it.

Although I'd tested it already, what I've learned is that you need to remove from circuit to properly test these things. If I'd thought about it properly, of COURSE I needed to. Otherwise the current from the base would have simply found it's way to the collector (earth) through the coil at T2, as was mentioned above (Duh!).

Well, you learn from your mistakes.

Anyway, time to see how expensive and available these TV transistors are here in NZ. Certainly my local electronics hobby store doesnt stock it.

Thanks to all who helped with this.

[EDIT]: Looks like I can get the transistor from a local South Island firm here for about $5 total (incl. shipping)

Tez

Unknown_K
April 9th, 2009, 09:35 PM
Most parts are cheap, figuring out what to replace is not.

arjoll
April 10th, 2009, 01:26 AM
As I understand it Q3 is a power transistor whose function is to pulse voltages on and off phase to get a horizonal sweep. Is this correct? If so, could I use a scope to test it?
You probably need to scope out what's happening before that. If you're just looking at DC voltages then you're not seeing anywhere near the full story, and if you're just looking at AC voltages on a DMM then the readings could get messed up, depending on the waveform - certainly in this case you're not going to see anything useful.


Thanks Andrew, but it's not worth bothering anyone about (except for the guys on here of course...we like that kind of thing :) ).
Yes, but you don't want it to beat you, right :)


Andrew, will Farnell ship single components like that and don't they have to import them (shipping charges?) I have a feeling the minimum order is $10.
They probably do have a minimum, but usually I'll end up spending more than $10 whenever I buy stuff, never hurts to have some stock :) Freight is probably more of a drama, I know RS charge NZ$10 and suspect Farnell are similar. Trade-Tech probably have the transistor as well, didn't think to check there.

BTW Its never a struggle for me to make the $25 minimum Trade Card order level at Jaycar either ;)


A check on the base<---> collector showed infinite resistance BOTH ways! This is unusual, even for one of these power transistor right?
Yes, sounds like a potential problem.

What caused it to fail though? It may just have given up, but that's why I'd look at replacing a few caps, running some basic tests on the LOPT and maybe checking resistors around this area (although they are probably fine, never hurts to check). Out of circuit of course!


Although I'd tested it already, what I've learned is that you need to remove from circuit to properly test these things.
Absolutely! There's very little you can get a good idea of in-circuit.


[EDIT]: Looks like I can get the transistor from a local South Island firm here for about $5 total (incl. shipping)
Grab a couple, just in case :) Never hurts to have a few spares!

linemanduke
April 10th, 2009, 05:28 PM
is the fly back the same for the mac classic? i have a junker here (no sound scsi problems) you can have the analog board for if its the same.

tezza
April 10th, 2009, 08:54 PM
is the fly back the same for the mac classic? i have a junker here (no sound scsi problems) you can have the analog board for if its the same.

I'm not sure they are the same. The Classic analogue board is different, I'm fairly sure of that.

Besides, I think I've got the problem identified now. When the transistor replacement arrives, hopefully I'll have a happy Mac SE.

Thanks anyway, I appreciate the offer.

Tez

tezza
April 15th, 2009, 02:11 PM
Ok, just to close this thread off...

The new transistor arrived yesterday. First thing I did was to measure the resistance across the various pins. Hmm...strange, quite similar to the one I removed. Maybe that one wasnít broken after all?

Anyway, soldered it in, assembled, and plugged it in. Still nothing on the screen. Measured the voltages around the transistor on the board. Same as the measurements with the old transistor. Hmm..

Suddenly the hum of the fan changes tone. It starts to slow down. Uh oh...now we have magic smoke...coming from where though? Hard to see...maybe the power supply. Or perhaps further up the analogue board. Fan grinds to a near halt. I switch off.

Ok, so that didnít go so well (-:

Checking the unit I discover a few things.

Iíd forgotten to plug the flyback lead, back onto the side of the screen (duh!). There are just too many damn connectors on an SE..lol

The transistor had a crack in it? This was either from it burning out (maybe this is where the smoke came from), or from me over-tightening the screw which secures it to the Flyback cage.

So, time to take stock. The transistor has cracked and the power supply has failed. The former could have been because I over tightened it. Then again, perhaps it was because I didnít plug the flyback into the screen? Maybe this is also why the power supply has failed. A cap could have blown in the latter?

It could be that the transistor wasnít even faulty in the first place and that some undiagnosed issue still lurks (the fly transformer?) along with a few other problems now.

Anyway, Iíve decided to end my Mac misadventure with this machine. I have four other classic Macs (including an SE/30) so there is just not enough motivation to persist with this one, despite the fact I donít like being beaten by it.

Itís good to write about successes, but more of the learning actually comes from the failures. Iíve learnt to...


Always check all leads carefully to make sure they are plugged in. Itís easy to miss one where there are a few
Large transistors with a screw hole at the top shouldnít be screwed in too tightly (although this might not have been the cause of failure in this case)
Check components when out of circuit or readings can mislead you

As to the SE, the tube is a useful spare part, as itís swappable with the other Macs. Cases can be used for aquariums of course (but I'm not really into fish). The SE logic board would make a good wall hanging (http://vectronicsappleworld.com/macintosh/boards.html)! Now this is a distinct possibility. :)

Thanks for all the comments and help. They are appreciated.

Tez

linuxlove
April 23rd, 2009, 07:45 AM
well, after reading your blog bost on the dead mac se and how you said that you ran out of things to fix, here's my advice for curing that problem:

take work slower! :rolleyes:

well, i guess there's nothing wrong with doing fast work as long as you know what you're doing :D

tezza
April 23rd, 2009, 06:10 PM
well, after reading your blog bost on the dead mac se and how you said that you ran out of things to fix, here's my advice for curing that problem:

take work slower! :rolleyes:

well, i guess there's nothing wrong with doing fast work as long as you know what you're doing :D

Yes, it's the "know what you're doing" bit where I often come unstuck.

The blog entry linuxlove speaks of is here (http://www.classic-computers.org.nz/blog/2009-04-23-Mac-SE-resurrection-bridge-too-far.htm). Essentially it's a summary of the latter part of this thread.

I am curious about the power transistor though (see blog). Is the middle leg always regarded as the base and should should resistance between emitter and collector always be infinite when measured across the these pins when out of circuit? That's what I've always assumed but maybe these assumptions are incorrect?

Tez

cosam
April 24th, 2009, 02:42 AM
I am curious about the power transistor though (see blog). Is the middle leg always regarded as the base and should should resistance between emitter and collector always be infinite when measured across the these pins when out of circuit?
Oh, the pinout can definitely vary. Most of what I've come across are ECB or CBE configurations (or indeed the reverse depending how you look at it). Your Q3 (a BC406) is of the former type. If you screwed it to the bench, pins towards you, the order would be BCE from left to right.

BTW: I don't suppose you have a transitor test setting on your multimeter? I never realised I had one until I looked last night! There's an "hFE" setting on the dial and two rows of four holes for plugging in the transistor.

tezza
April 24th, 2009, 02:52 AM
Oh, the pinout can definitely vary. Most of what I've come across are ECB or CBE configurations (or indeed the reverse depending how you look at it). Your Q3 (a BC406) is of the former type. If you screwed it to the bench, pins towards you, the order would be BCE from left to right.

Ah. That would explain it. That original transistor was probably ok then, not faulty as I thought. Well, now I know. Thanks.


BTW: I don't suppose you have a transitor test setting on your multimeter? I never realised I had one until I looked last night! There's an "hFE" setting on the dial and two rows of four holes for plugging in the transistor.

No, I don't but I am aware some meters have them. I have an el-chepo meter someone gave me as an Xmas present. It does the bare minimum really. But then, I never expected to be tinkering around with electronics.

I need a better one really.

Tez

nige the hippy
April 24th, 2009, 10:25 AM
I got a meter for my brother in law for about £6 (he didn't need anything special) I was surprised to note the "Buy one, get one free offer" on them so I got a spare meter with a diode-test setting for £3. and it seems pretty accurate. My "proper" meter is a decent one though.
I use the diode test (and continuity beep) a lot.
I'm sorry to have led you down the garden path with the transistor though, however I would have been looking at it at that point, but done a diode test & discounted it as OK!

tezza
April 24th, 2009, 11:56 AM
No worries Nige. If I'd known that transistors could vary on the orientation of their pins, my resistance measurements would have also cleared the original one as OK.

In some ways it's good, because with all the associated smaller components checking out ok, it must have been the flyback which was faulty. So I can be satisfied I did all I could to diagnosis it, and fixing it would not be possible.

I don't have to feel guilty from it's accusing stare from the junk pile now. :)

Tez

Terry Yager
April 24th, 2009, 05:58 PM
I don't have to feel guilty from it's accusing stare from the junk pile now. :)

Tez

Putting a round thru it's cyclopian eye also helps to alleviate those guilt feelings...

--T