Help me identify this 286 motherboard \ VOGONS

Help me identify this 286 motherboard

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First post, by mandm_nl

Posted on 2022-10-20, 13:32

mandm_nl Offline

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I found this online and it doesn't work (yet). In order to troubleshoot it I need to figure out which motherboard it actually is and hopefully find some information on the switch settings it has as well as other documentation or BIOS images. All I have is the B286-4MF printed on the board.

Right now it has quite an erratic behaviour. Most times it will not POST at all and you will just see ---- on the analyzer. Sometimes it decides it does want to try to boot and it will only give you two POST codes: 12 01. Without knowing the type of BIOS it is difficult to understand what those codes mean. What I do know is that it will also beep by telling you it doesn't see a videocard (even though one is present). In my research I found a couple of BIOSes that have these possible codes. I measured the 5V lines up to the CPU and those look fine and stable.

AMI:
01 NMI is disabled and the i286 register test is about to start
12 64KB base memory test OK

AST:
01 Test CPU registers
12 Test DMA page registers (EGA.VGA vertical retrace failed)

AT&T:
01 CPU test
12 Display controller test

Chips & Technologies:
01 CPU flag register failed
12 Task register failed, Keyboard controller failed

Based on the beep codes it seems reasonable to think that this board has either an AT&T or an AST BIOS. But I might be wrong here.

So, does anyone have any clue to who made this board and perhaps even has some info on the settings?

Reply 1 of 8, by BitWrangler

Posted on 2022-10-20, 14:33

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IMO anything with a bunch of sockets like that that has been sitting more than 2 years needs everything pulled and reinserted, with a pass of IPA or contact cleaner over everything. You go "Ah yiss, sockets, will be super easy to troubleshoot....." then some period of ownership later "Fracking sockets, gotta troubleshoot it all the damn time..."

Unicorn herding operations are proceeding, but all the totes of hens teeth and barrels of rocking horse poop give them plenty of hiding spots.

Reply 2 of 8, by mandm_nl

Posted on 2022-10-23, 20:13

mandm_nl Offline

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BitWrangler wrote on 2022-10-20, 14:33:

IMO anything with a bunch of sockets like that that has been sitting more than 2 years needs everything pulled and reinserted, with a pass of IPA or contact cleaner over everything. You go "Ah yiss, sockets, will be super easy to troubleshoot....." then some period of ownership later "Fracking sockets, gotta troubleshoot it all the damn time..."

I did this today but it didn’t help.

Reply 3 of 8, by mandm_nl

Posted on 2022-10-28, 18:39

mandm_nl Offline

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So I got the board to POST again. I made a rookie mistake. The battery was removed obviously, but with older boards it can happen that they don't want to post without a battery. This is one of those boards. It does POST (yaay), but it also seems to overheat and freeze. If you run it long enough it will fall back to not giving a POST and only the four "-" on the POST analyzer.

I hope it's a faulty CPU and not microcracks in the board itself. Without any experience in this I think microcracks are a real nightmare to find and resolve.

I'm open for suggestions on what other possible causes could be.

Reply 4 of 8, by BitWrangler

Posted on 2022-10-28, 20:17

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You might be in for a session of thumb test and freezer spray (or canned air inverted) to see if you can spot anything overheating or cure it, or cause it even with hot air.

Unicorn herding operations are proceeding, but all the totes of hens teeth and barrels of rocking horse poop give them plenty of hiding spots.

Reply 5 of 8, by mandm_nl

Posted on 2022-10-28, 21:26

mandm_nl Offline

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I did some tests and I think I have isolated it to the clock crystal. It is socketed but somehow it doesn’t make good contact. If I put pressure on it things start working again. Either the contacts of the socket are bad or the crystal itself isn’t in the best shape. Either way it might be best to at least directly solder it in place instead of in a socket. If that doesn’t solve it I can replace it with a new crystal.

So far I was able to boot into DOS and run the BIOS setup program. It all worked quite stable actually. But beware of touching that crystal or in any way disturb it or it will all come to a grinding halt.

Reply 6 of 8, by BitWrangler

Posted on 2022-10-29, 04:10

BitWrangler Offline

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A common thing to see, was the crystals ziptied into the socket. So maybe they have a natural tendency to walk out anyway.

Unicorn herding operations are proceeding, but all the totes of hens teeth and barrels of rocking horse poop give them plenty of hiding spots.

Reply 7 of 8, by rasz_pl

Posted on 2022-10-29, 07:39

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crystals and oscillators do age

https://github.com/raszpl/sigrok-disk FM/MFM/RLL decoder
https://github.com/raszpl/FIC-486-GAC-2-Cache-Module (AT&T Globalyst)
https://github.com/raszpl/386RC-16 ram board
https://github.com/raszpl/440BX Reference Design adapted to Kicad

Reply 8 of 8, by mandm_nl

Posted on 2022-10-29, 07:59

mandm_nl Offline

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So my to do list seems to be this:
1. Replace oscillator and maybe solder it in place instead of the socket
2. Replace BIOS chips as they may also have read issues which can cause this behaviour
3. Get more RAM for this board

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