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486 motherboard doesn't boot

Agent Orange

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Sep 24, 2008
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6,111
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SE MI
The OP said: if I start the computer again the card doesn't show any code (and doesn't boot neither), I have to press the reset button to get thoses error code again. Any tips or suggestion is welcome :) Thanks.

That indicates, at least to me, that there is a 'power' problem somewhere on the board. Possibly a cap breaking down. I think the board has more than logic issues.
 

twolazy

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May 22, 2011
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Chicago, IL
I would give the board a nice bath, just in case any residue from leaking caps is preventing it from successfully booting...
 

tradde

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Apr 30, 2003
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Katy, Tx
He says it don't boot. But what does that mean? No power at all or it just hangs somewhere before getting to start the POST? I never assume anything. Well, sometimes I do but it usually bites me later. :)
 

vbug

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Jan 2, 2021
Messages
27
Location
France
Hi everyone, and thanks for your suggestions. I finally changed the keyboard controller chip I was suspecting to be faulty, no change. I already tried with another (identical) CPU and RAM, nothing. I know the AT PSU works correctly too.

I'll precise the behaviour : when I turn on the computer, the PSU fan runs, always in any case. I got some POST codes on the post card, but the screen doesn't turns on at any moment, there is no beep at all, and it hangs with the 0D-0C code on the post card (0D is the meaning one, 0C the previous one) for maybe 1min then it turns to 00-0D code. As a precision, there is a "Powergood Select" jumper on the motherboard, when that jumper is on its initial configuration (the one who worked for years), "normal mode (default)", the post card gives the mentioned code sometime only, otherwise it show -- -- (no codes) like if the board doesn't run/do anything at all. In that situation, pressing the reset button can sometime trigger the initial behaviour with mentioned codes on post card (but still screen off and no beep). When I switch that Powergood jumper to "For 80486 New Version", the post card shows always mentioned code. I took a look on the signification of that "powergood", it seems to be related to power supply check before launching the initialization of the motherboard and components. That could means there is a power issue somewhere. But I checked the voltages on one ISA slot, it seems to be correct (5.1v on 5V lines, 12.3v on 12v lines). I don't really know how I can check capacitors more than check if there is not a shortcut on them, any suggestion on that ? Thanks.
 

tradde

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Apr 30, 2003
Messages
1,262
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Katy, Tx
Are you sure that POST code chart matches your BIOS? You show you have an AMI Bios chip. But 0D has no text. That seems odd.
 
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