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8590 with two symptoms: failing XGA and hangs of floppy access

booboo

booboo

Experienced Member
Joined
Sep 13, 2009
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172
Location
Dallas, Texas, USA
I have this IBM PS/2 Model 90 XP 486 (8590 Type 1 Complex) parts system that keeps doing the following:

  • on (very often) occasion, on boot up it gives (1) Long (2) Short beeps, indicating a bad/missing video. Video is present sometimes, scrambled others, and missing altogether the rest of the time. I've removed and reseated all the VRAM ZIPPs, and reflowed the DB15 solder joints. But still occurs...
  • the floppy drive no longer works (I have replaced with known good and same issue). The drive from this machine works on another PS/2... The actual symptom is that when I try to access the floppy (by either attempting boot from it or from DOS if booted from HDD), the system spins the floppy and then hangs. No ALT-CTRL-DEL for me... I need to turn power off. So to me it seems be a problem on the planar floppy controller circuit.
Likely unrelated symptoms but thought I should check. FYI, I've also replaced the processor complex with a known good one, and same issue.

Question for the sages: could this be capacitor related? The capacitors on the planar look ok, but I have not removed and tested (I don't have an ESR capable tester...). I don't see any corrosion or leaking.

PS: If the system *does* boot ok with video, then it seems to works just fine and I can launch and play games, etc. Floppy drive now no longer works at all.
 
Last edited:
Well, quick update. I've recapped the whole planar (system board) and no change to behaviour... I'm now beyond my capability of further troubleshooting this system. I know it's the planar, but out of options on what to do.
 
Systems of that vintage often have a whole lot more than just capacitors go bad. Logic and RAM ICs can fail, as can GAL/PALs and EPROMs.

Unless an IBM guru comes in and immediately knows what the issue is, you're looking at having to get a logic analyzer, logic probe and possibly an oscilloscope and start hunting for bad ICs.

But before that, I'd recommend cleaning all of the cards and motherboard to within an inch of its life. With all of the cards removed, blast the slots with electronic connector cleaner (the generic stuff from home depot or auto parts stores), give them each a light scrub with a soft bristled toothbrush and let it dry. Then go back and use a small amount of deoxit gold in each slot and on the card edge connector on each of the cards. While the cards are still wet with deoxit gold, plug and remove them from their respective slots several times.

To me it sounds like either an intermittent connection (hence the above cleaning) or dodgy IC(s) that behaves or misbehaves based on heat or stress.

If you need an ESR tester, I'd recommend this:

https://www.ebay.com/itm/222520569499

It's pretty good to use to weed out duff capacitors, you just have to understand the numbers it tells you to determine that. Like if you put a capacitor in and it thinks its a diode, you know it's bad. But it can be a bit tricky if you put a 1800uF cap in and it measures something like 2560uF. In this case it would be bad, the capacitor tester is giving an errant result because the capacitor is electrically leaky. It can also measure ESR, but you need to use a chart to determine how much ESR is too much for different value caps. Higher voltage capacitors and very small capacitors tend to have higher ESR and won't explicitly be bad.
 
Thanks! Indeed, when I got the system I cleaned everything as described. All connectors where cleaned with an eraser and DeOXit. EPROMS removed, cleaned and reseated as well. VRAM as well as mentioned. I'm actually leaning towards a cold solder or broken trace (at least on the video) due to the mechanical effect I mentioned (putting pressure on VGA connector corrects the errors).
 
Hopefully its a mechanical problem and not something like bad VRAM because ZIP memory of any type is unobtanium. The only way to really get it is to cannibalize other machines with it, new old stock is pretty rare.
 
Have you tried swabbing the edge connectors with a very damp Q-tip? I do that for memory and cards all the time. I am told a pencil eraser works as well.
 
I just got a Model 80 with similar floppy issues (hang on boot). Doing a bunch of googling lead me to some posts recommending replacing the caps on the floppy drive. Like magic, it started working! This thread was helpful for me: https://www.vogons.org/viewtopic.php?t=46462&start=20

I do have an XGA adapter in this system as well, but I don't have the issues you are having with that board.
 
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