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Need help indentifying 386SX MB

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First post, by Cbb

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Hi guys,
Recently got this beauty. But it doesn't POST at all (dashes on my tested POST card). I did not found any defects except minor corrosion at the corner by the keyboard connector but it doesn't seem to affect the common board fuctionality.
First of all I went to TheRetroWeb to get the BIOS but it seems like there's no such board in the database. At least there's one like mine but still no BIOS/manual etc.
My board got markings: "MIKE/25", "P/N 30-000223-00", "osj robert 10/02/1991", "AIO3125/P". Web search lead to nothing.
Tried to program 27C512 EEPROM with a BIOS from another board with same chpset but no luck.
Also tried to dump the video BIOS with my Stager VS4800 but it claims about bad IC legs contact. Dunno the exact EPROM type, tried to choose generic winbomd/atmel 27C64.
If anyone got a such board working, please reply with both main and video BIOS dumps.
Also if you've got any thoughts on why the board doesn't POST I will be much appreciated to see your comments!

Reply 1 of 5, by Rwolf

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It' might be some prototype or clone of Commodore's PC efforts; the layout has some similarities with this motherboard:
https://www.commodore-info.com/foto/computer_pc386_25_04.jpg

Also I see OSC4 seems to be missing; RAM refresh clock maybe?

Reply 2 of 5, by konc

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Cbb wrote on 2025-05-16, 11:02:

I did not found any defects except minor corrosion at the corner by the keyboard connector but it doesn't seem to affect the common board fuctionality.

It does seem to have a certain amount of corrosion around the battery and the keyboard bios, I wouldn't be so sure it's minor, even traces seem affected. I'd grab a multimeter to confirm basic continuity and since you get nothing out of it also of the power connector which is in the area (remove keyb bios too).

Reply 3 of 5, by Cbb

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Rwolf wrote on 2025-05-16, 13:17:

It' might be some prototype or clone of Commodore's PC efforts; the layout has some similarities with this motherboard:
https://www.commodore-info.com/foto/computer_pc386_25_04.jpg

Also I see OSC4 seems to be missing; RAM refresh clock maybe?

Thanks for reply.
The common layout looks similar but location of BIOS/Chipset/CPU/coprocessor chips are different. These boards are not relativies though at first glance they're look like.
about missing OSC4. I'm not sure it is needed at all. Looking at pics of 386SX boards on RetroWeb I do see boards with unopulated crystals.
I do not have on hand any OSC of such formfactor to put in and to get the silkscreen with it's clock fully uncovered I need to desolder the socket. If I would not find any exact info on my board I'll probably will swithch my desolering gun on and order a proper one.

Reply 4 of 5, by Cbb

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konc wrote on 2025-05-16, 14:23:
Cbb wrote on 2025-05-16, 11:02:

I did not found any defects except minor corrosion at the corner by the keyboard connector but it doesn't seem to affect the common board fuctionality.

It does seem to have a certain amount of corrosion around the battery and the keyboard bios, I wouldn't be so sure it's minor, even traces seem affected. I'd grab a multimeter to confirm basic continuity and since you get nothing out of it also of the power connector which is in the area (remove keyb bios too).

yep, the bottom trace on the 2nd pic looks really sick. will check it and the surroundings tonight. thanks!

Reply 5 of 5, by Matth79

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OSC 4 is most likely an async clock option for the FPU

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