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Parity check

Chances are the PS/2 BIOS is using 1Kb for extended data. Don't worry about the 639KB.

Edit: bah I pressed submit too late!
 
modem7 said:
Yes. I can see why.
Today is International Day of Spelling and Grammar, and in post #12, you have used "it's" instead of "its".
Click to expand...

I ran my XT-IDE rev 2 for the rest of the night with a space 28c64 EEPROM, and I did not have one single crash.

It was a faulty EEPROM this entire time.
 
evildragon said:
I ran my XT-IDE rev 2 for the rest of the night with a space 28c64 EEPROM, and I did not have one single crash.

It was a faulty EEPROM this entire time.
Click to expand...

Ok, so it crashed again.

But I found out what's causing it cause I can make it happen on-demand.

The new AC unit that was installed in our house, is what's causing it.. Every time the heat pumps compressor kicks in, is when the IBM crashes.

Ugh, couldn't it have been a more "normal" issue?
 
Presumably the compressor isn't soft-start (DC-Inverter)? So it's likely brown-out at the supply; I'm thinking dried-out electrolytic caps in the PSU.
 
pearce_jj said:
Presumably the compressor isn't soft-start (DC-Inverter)? So it's likely brown-out at the supply; I'm thinking dried-out electrolytic caps in the PSU.
Click to expand...
I don't know what these new Trane compressors use, but it sounds like it starts pretty hard.

I removed the motherboard in preparation of checking things while it was outboard, and I was greeted with this while it was outboard..

Can you spot the "problem"? All I'll say is, if this was like this for a while, this poor sucker has been starving for amps on the motherboard.

http://img.photobucket.com/albums/v395/Evilweredragon/problem-1.jpg
 
It would be interesting to plug a multimeter into the wall socket and watch voltage drop when the compressor kicks in.

What's that red wire? Looks to be an orphan or an escapee?
 
Yes, it's the 5v rail going to the motherboard..

So, I would assume, if this wire has been working it's way loose to the point of not even connecting, then no wonder a AC compressor is causing it to fail, it's already being deprived of amps.

I fixed it and am testing again.

But I found it interesting that the BIOS chips are getting rather warm on this motherboard.. The two chips are 118F each, the RAM is cooler than that.
 
evildragon said:
....

The new AC unit that was installed in our house, is what's causing it.. Every time the heat pumps compressor kicks in, is when the IBM crashes.

.....
Click to expand...

I had a similar problem with a PCjr many years ago, it would just randomly reboot at times. Spent a lot
of time trying to figure out what the problem was.....one night I just happened to be in another room
of the house, and heard the A/C kick on, just as I saw the screen on the PCjr rebooting in the other room.
Turned out the brick power supply was affected by the voltage drop.
 
evildragon said:
So I fixed the wire, and so far no problems when the AC kicks in. So that broken 5v rail mail have been the problem.

But because the planar was so caked with dust, I took it out and decided to use a brand new tooth brush and rubbing alcohol and give it a cleaning.

http://img.photobucket.com/albums/v395/Evilweredragon/model25planar.jpg

http://img.photobucket.com/albums/v395/Evilweredragon/model25planar2.jpg

So far so good..
Click to expand...

Gah! Didn't work. So I replaced the BIOS EPROM with the CMOS ROM version. Same thing.

I measured the house AC voltage when the air conditioning turns on as it still seems to be the trigger, but my analog meter showed NO movement of the needle when it kicked in.
 
Well this has to be the strangest thing I've ever seen. I took apart the model 25 and took a look at the power supply with an ESR meter and all the capacitors are fine. Then I noticed, once again with the XT – IDE card removed the computer does not freeze no matter what. So because it was memory related I changed the EEPROM with a different one but it still did it. I then tried with the disk on module removed and booted from floppy. Still freezes when the ac compressor kicked in. So I installed the original rev 1 XT - IDE and it works perfectly fine no crashes at all.

What the hell? Is it possible that a tantalum capacitor got damaged during soldering and is having issues?
 
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