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PS/2 P70 Display/POST fault?


Experienced Member
Jan 27, 2008
United States
Yet another P70 thread, woo, let's goooo.

Pulled my P70 out from storage and turned it on for the first time in 5 years. no display, ominous POST beeping of one long, two short. Okay, looks like a plasma controller board issue. Pull it out, verify the machine behaves the same way, good.
Recapped the controller board. two 16v 10uF, one 16v 47uF, one 25v 22uF. used some known-good reclaimed caps from my stash. Dropped that back in with cleaned contacts, and it POSTS. get it back together and the plasma doesn't work. but I'm still getting POST, so roll with it. Drop in a WDC ethernet card so I can back the machine up. ADF file on the config floppy, drivers, mTCP stuff, done. Halfway through the copy, VGA display starts flickering a bit. Alright, not that big a deal, probably just my monitor. By the end of the network backup, I had completely lost red.

Reboot, thinking it's just a fluke of my monitor, same result. and now it's giving the dreaded 14902 error. So back out it comes, re-replace all the capacitors again thinking one of them is bad, and being unsure where they connect is the issue.
Plug back in, doublechecking my work, and whoops, no POST. not a bit. unplug and doublecheck the board does any sort of POST beep without the card installed, and nope. no dice. Board is unresonsive. 386 gets warm, as do the metal can chipsets, and the 74Fxx logic by the controller board connector, but no dice. even pulled the MCA riser out, and put the WD NIC on the other side of the room thinking it was emanating bad joojoo, and still, no dice.

So far have been inside and out with this system and even went so far as to remove the PSU and re-go over all the fixes in there I did 5 years back with regards to fixing broken solder joints and even reflowed a good chunk of the board. All the voltages coming out of the PSU not on the HV side look good. I dare not even try checking the voltages on the HV side as I know the plasma is in good shape and works (it blips when disconnected from the plasma card), plus my meter isn't rated to go that high.

First suspect on the list I'm thinking is capacitors on the mainboard are finally giving out, but that doesn't explain the weird behavior from the plasma card.

I'm out of options. I'm gonna probably end up bringing this to VCFMW in September to sort this out with people that are more talented at this than I am... because I've reached the limit of what I'm capable of.
for the record, the plasma card FRU is 38F4686 and the planar FRU is 56F9085, both the "new" boards. Floppy isn't any issue, it's been replaced in the past with an adapter. FPU on the board is a Chips J38700DX, having that in or out of the machine changes nothing, and the machine doesn't even give an error beep when the RAM is yanked.

Any help towards figuring this out would be gratefully accepted... I just don't even know where to turn at this point.