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FIC PA-2013 and K6-2/500 no longer POSTs

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First post, by appiah4

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One of my builds with a FIC PA-2013 and a K6-2/500 no longer POSTs. Even the CPU/Case fans don't speak and there is no voltage on the pin headers. The AGP card gets voltage and gets warm but the CPU is cold as ice, as is the chipset and RAM. I tested with a different and known good PSU and it made no difference. There are no beeps whatsoever. Any ideas as to what this could be? What is more likely to have failed while sitting in a well ventilated storage, the board (VRMs? Capacitors maybe - though I see nothing bulging..) or the CPU? I have no Socket 7 CPUs with me currently to test unfortunately, but I will do that first thing during the work week..

Retronautics: A digital gallery of my retro computers, hardware and projects.

Reply 1 of 8, by Horun

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Could be a bad cap, or failed mosfet. Did you replace the coin cell battery just to eliminate that as a possible ?
I would check the volts on center tab of the mosfets to see if delivering any volts.

Hate posting a reply and then have to edit it because it made no sense 😁 First computer was an IBM 3270 workstation with CGA monitor. Stuff: https://archive.org/details/@horun

Reply 2 of 8, by appiah4

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Horun wrote on 2020-09-05, 18:53:

Could be a bad cap, or failed mosfet. Did you replace the coin cell battery just to eliminate that as a possible ?
I would check the volts on center tab of the mosfets to see if delivering any volts.

Coin cell is fine.

Do you mean checking the D of the Mosfets against motherboard ground for voltage when powered up?

Retronautics: A digital gallery of my retro computers, hardware and projects.

Reply 4 of 8, by Miphee

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Desolder it, measure resistance between G-S and G-D. If you measure any value the MOSFET is bad.
Switch to diode mode, measure between D-S while G-S are shorted. One direction should show nothing, the other should give you a stable value.

Reply 5 of 8, by appiah4

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I will first try with a different CPU, Then desolder and test the mosfets..

Retronautics: A digital gallery of my retro computers, hardware and projects.

Reply 6 of 8, by appiah4

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Well.. I tried this board with two different PSUs using the same stick of RAM and same K6-2/500 CPU and it was a no go. So I took it upstairs, hooked it up to an FSP 300W PSU I had lying about with a K6-2/400 I knew to be good, and it fired up.

Now get this: I put the K6-2/500 back in and it fired up again.

What gives? I would say bad PSU but I tried the board with a rock solid 500W PSU before and it didn't boot.

Retronautics: A digital gallery of my retro computers, hardware and projects.

Reply 8 of 8, by appiah4

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shamino wrote on 2020-09-09, 00:23:

With the 500W PSU attached, check voltages. Maybe one of the rails isn't holding up.

No, the PSU is fine, tested thoroughly.

I think it has to do with RAM. I have tested the board with a few different sticks of RAM and it exhibits the same behavior with some. Although that hardly explains why it now boots with the stick it refused to boot earlier.. Weird.

Retronautics: A digital gallery of my retro computers, hardware and projects.

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