Wilius wrote on 2020-08-16, 00:17:

Despite the fact, that I already know, which chip got damaged, I still meassured for continuity. […]
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Despite the fact, that I already know, which chip got damaged, I still meassured for continuity.

Here is what I meassured so far:

Power Connector 1:
+12v 1909 (with CPU board installed: 1890)
[...]

Although I most likely can not help you with your board, as I don't have a Schneider VGA AT System for reference measurement, I would like you to clarify what measurement mode you used. The "continuity test" mode is a kind of "secondary function" on most multimeters, either in the "200 Ohms" or in the "diode test" mode. Because the values you showed are without a decimal dot, I guess the values are to be read as "millivolts drop" in "diode test" mode. I also guess you put the black lead onto some kind of ground all the time, and probed the power supply and CPU board connectors with the red lead.

Confirming the guesses helps other people to reproduce your measurement and check for significant differences. I like your scientific approach of providing a lot of data to support the research what might be broken on your board, but I feel it needs even better documentation about the boundary conditions. It also might be useful to know the (coarse) current your multimeter uses in continuity test. If you happen to have a second multimeter, please connect the multimeter you used for the continuity test to the current range and report the value. I expect a test current between 1 and 10 milli ampere, so starting with the 20mA range should be fine.

mkarcher wrote on 2020-08-16, 10:03:

I also guess you put the black lead onto some kind of ground all the time, and probed the power supply and CPU board connectors with the red lead.

It's true, I indeed did that.

I'm going to provide more acurate docummentations next time, but this might take a while.

Thanks for your help mkarcher. I really appreciate it.

I just realized something. There is a reason, why it's called: If it ain't broke, don't fix it.
I didn't listen to that very sentence and got punished for it.
This will be a life lesson for me.

Wilius wrote on 2020-08-16, 11:06:

I just realized something. There is a reason, why it's called: If it ain't broke, don't fix it.
I didn't listen to that very sentence and got punished for it.
This will be a life lesson for me.

Very true and wise, but also I like a twisted version of it: "You don't really know how your stuff works until you broke it and fixed it yourself". In the case of the VGA AT System, you might be out of luck with that chip that looks like it is a proprietary Schneider chip. Time to call Captain Hindsight - but as usual, he will not be really helpful.

Yeah, you are absolutely right.
Well, I guess the IO Board is bricked.
But maybe I have better luck with the CPU board.

Would it makes more sense to remeassure the IO- and CPU Board with a oscilloscope?

Wilius wrote on 2020-08-16, 11:22:

Would it makes more sense to remeassure the IO- and CPU Board with a oscilloscope?

I don't think random oscilloscope measurements are useful without an understanding of how the signals should look like. And you won't get meaningful oscilloscope measurements unless most of the chips are at least partly working. As long as something shorts a power rail, oscilloscope trace of signal lines are useless. Oscilloscope traces from either the IO or the CPU board might also be of limited use, as the computer will start doing sensible things only of the two boards are connected.

So you would first need to basic reverse engineering to know which pins are data pins, which pins are address pins and so on, and then you might find pins that behave odd. Without schematics, this will get very tedious. You might like to watch the video series from Adrian's Digital Basement where he fixes a TI99/4 computer, and bricks his replacement CPU on the course, as a consolidation that you are not the only one bricking chips while working on retro hardware - and also as hint on how tedious and difficult finding faulty parts is even with an oscilloscope and schematics at hand, see https://www.youtube.com/playlist?list=PL4tFqF … 6a2GphiStcqo1eR.

If you are sure that no short circuits remain on power lines, i.e. all supply voltages are nominal when you turn the thing on, you can make a kind of "guided tour" with the oscilloscope, though. Check for the clock line first. Check for bus signals on the 80286. Check for ISA control signals. Check for address, data and control signals at the ROM chip. Check for chip-enable signals on support chips like the keyboard controller. Disassemble the BIOS to find out in what order the support chips should get accessed.

The BIGJIM, and the JIM variant of that same chip, is a custom chip. I fear that there is no replacement for it unless you get one from a donor board.

I too was afraid of that.
I guess this is the end of it. Bummer.
Gosh, i'm such a f *** ing idiot.
I apologize for what I have done. I really feel down in the dumps right now.
RIP Schneider VGA AT System 70 CEG. You didn't deserve to die.
If anyone happens to know, where I could get a cheap doner Board, that'd be awesome.
Anyway. I better stop here, before I make it worse.
Well, sometimes you win and sometimes you lose.
However, I'm still going to provide more acurate meassurements of the CPU Board. If nothing gets in my way, this will happen next weekend.
Thanks for anyones patience.

My puppy tried helping me to fix my 286. Well... let's put it that way. He yet has to learn, how to properly disconnect a cable.
Jokes aside, I can't blame him. I have to admit, that leaving him in my room without supervision, was a pretty dumb idea.
And I thought, it couldn't get any worse. Oh dear, this project has become a complete train wreck. I apologize for the inconvenience.
I think it's time, to move on, and call it a day. I've learned from my mistakes and won't do them again next time.
Thanks for anyones help. You guys are amazing.

Wilius wrote on 2020-08-16, 00:17:

There is visible damage, on a chip labled "Schneider BIGJIM 50773". Is it possible to find a replacement? [..] I beg your pardo […]
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There is visible damage, on a chip labled "Schneider BIGJIM 50773".
Is it possible to find a replacement?
[..]
I beg your pardon

I hope someone can help me, to find that chip.
Thanks in advance for your help.

Hi, I'm not 100% sure, but perhaps I've got that chip among my spare parts.

So please don't throw your board away yet.
(Also, the RAM and 286 CPU are still useful)
- I'll also check my documents, maybe they contain something useful to you.

Anyway, I recommend making a pause.
Things work out better in the end if you take a rest from work.

Hi Jo22
Thanks for you reply.
1. Don't worry, I'm not planning on throwing it away.
Throwing it away would be a waste of vintage hardware.
2. If you could find that chip, that would be awesome. However i'm very certain, that it's probably not the only chip, which got damaged.
3. I think the majority of damaged chips are probably located on the CPU Board. I'm still searching for shorts. (Both on the CPU Board and I/O Board)
Do you got any suggestions, how I could perform the meassurements?
4. Do you really think, that CPU and RAM are still useful after the incident. I mean the whole thing got shorted out.
I also noticed, that the CPU gets pretty warm too.
5. Thank you for checking your documents. That's really kind of you.
6. What am I supposed to do with the destroyed cable of the front panel? Any chance, that I could fix it?
7. Thanks for your recommendation. I too think it's better to make a pause, before I cause more damage.

Wilius wrote on 2020-08-26, 17:10:

4. Do you really think, that CPU and RAM are still useful after the incident. I mean the whole thing got shorted out.
I also noticed, that the CPU gets pretty warm too.

Actually, the more quickly it shorted out, the better. As soon as the first component shorted out the power, the supply shut down and stopped damaging any further components. There are some circuits (not here) that create an artificial short circuit on purpose if an overvoltage is present to save more fragile components. If you do it on purpose, you call it a "crowbar circuit". If you are lucky, something acted as "parasitic crowbar" before most of the chips were toast.

Wilius wrote on 2020-08-26, 17:10:

6. What am I supposed to do with the destroyed cable of the front panel? Any chance, that I could fix it?

It looks like the cable can be carefully seperated into single wires near the damaged part, then you can cut it, put some heatshrink tube on one end of each wire, solder the wires and cover the solder point in heatshrink. It shouldn't even look that bad if done properly.

🙂

Hi!

I apologize for delay.
I've been quite busy and hadn't got any time to reply to your messages.
1. Thanks Mkarcher. These are great news. Looks like, i'm gonna fix the cable soon.
2. Thanks for the picture Jo22. May I ask, wheter this is the chip, you've got amongst your spare parts?

Wilius wrote on 2020-09-12, 20:12:

2. Thanks for the picture Jo22. May I ask, wheter this is the chip, you've got amongst your spare parts?

Hi, yes, it is. It's installed on an old Euro AT mainboard and should be fine. I can send the chip to you via mail no problem. And other chips, too, if you like. 🙂

That's fantastic, but I beg for your understanding, that I first have to ask my parents for permission, whether such thing is possible, cause i'm not an adult yet.
And I also have to check for more chips, that are faulty. I hope you don't mind.
I have yet another concern. How should I deal with the rear crack in the CPU Board connector? I don't wanna make the same mistake and fry the system again, once I fixed it.

Thanks in advance for your help and thanks for your amazing support!

Hello.
I asked my parents and sadly they weren't pretty happy about it. Nonetheless, I sort of got their permission, as long as it's not too expensive. (However, I'm going to ask again, just to be sure)
Therefore, I have some questions.
First, how much do you want for the chips? (Let's assume that the BIGJIM chip isn't the only faulty one)
Do you accept payment via PayPal?
And second, how high are the shipping costs? (I live in germany)
Thirdly, Are there any other costs?
As soon, as I can confirm, that my parents are ok with that, we can discuss how to move on.

Thanks in advance for answering my questions and thanks for your patience.

Hi again, sorry for the delay! It was weekend and I wasn't browsing Vogons.

No worries, I can understand your parents point of view.
The internet is a place full of weird people, some of which are harmless and some of which are not. 🙁

By coincidence, I'm from the same country.
Which makes shipping easier (~5-7€), but on the other hand isn't exactly making your parents any less worried (rather, the contrary) .. 🙄

So how about this: Instead of exchanging personal information (paypal, name, address),
please ask you parents for an address I can send a parcel too. It can be anything. A friend's address, someone's address at work, a post box etc. If they accept, just send me a PM. It doesn't hurry. I don't need to know your name, also.

In case they get suspicious why I ask no money for it:
In parts, it's because I'm a ham (amateur radio operator) - in German: Funkamateur.
And we're usually glad to help people and have an "Ehrenkodex" also, which means that (at least for some of us) money isn't everything. 😀
See https://de.wikipedia.org/wiki/Ham_Spirit

The other reason is, that I had to fix my Tower AT, too: Broken PSU, CPU card not working.
So I know how you feel. It would still be broken, if not about ~2 years ago a very friendly person helped me to fix it.

PS: If your parents don't know what a ham is, its a licensed "Radiobastler" essentially.
That beeing said, I'm a comparably young one, too (90s kid here). 😁

Hi
Thanks for your reply!
I like your idea! It's absolutely brilliant.
Right now i'm in a Internship, therefore, i'm probably not gonna write you the upcoming weekend.
If nothing gets in my way, I will try it the next weekend after that.

Hi there!
Merry Christmas everyone!

Thanks to Jo22, I finally managed to replace the Bigjim chip. I really appreciate his generosity.
Hopefully, I can finally continue to get my 286 running once again.
However I do have a few questions, before I dare to turn it on.
Next to the Bigjim chip, I also had to replace the cable for the frontpanel.
Thankfully I managed to order a identical one. However i'm uncertain, whether the pinout is the same too.
I would really appreciate, if someone who also owns this system could tell me the pinout for this cabel.
To give you an idea, how the pinout of mine looks like, I hastily made a diagram.
I know it looks atrocious, but I was in a hurry.
I decided, it would be better to replace the CPU as well.
Have I installed the CPU in the right way?
What else components should I check before I turn it on?
Thanks in advance for your help.

Wilius wrote on 2020-12-26, 14:23:

Have I installed the CPU in the right way?

Yes. The dot on the CPU is aligned with the corner of the socket that has the edge cut. It looks like it is firmly inserted.

Wilius wrote on 2020-12-26, 14:23:

What else components should I check before I turn it on?

You damaged a part of that computer by incorrectly inserting a card, so weird voltages were applied to some chips, if I remember correctly. Applying weird voltages is likely to damage chips in a way that they generate short circuits in places they don't belong. In "5V land", this is mostly harmless: Most logic ICs can withstand outputs shorted to ground or Vcc for some time without taking serious damage. On the other hand, if there are components that connect to +12V, -12V or -5V, you should test them for shorts between these supply pins and any other pins of that chip. Common chips that connects to +12V, -12V, +5V and logic signals on the mainboard are the 1488/1489 series serial port level shifters.