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Broken 386 board

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First post, by Kouwes

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I got a DataExpert 367C board from a friend that he put in store almost 30 years ago. It has a CPU, NPU, 8 x 1MB and 128kb of cache. Well, 128kb according to the jumper setting.
However, the board refuses to POST. My analyzer shows no activity but the CPU gets hot.

The battery is empty of course, but not leaking. I will replace it for an external 3 x 1.5V battery pack. Maybe then the board comes to life but I doubt it.
There are no visible blown tantalums but there may well be a shorted one, or even more than one.

So my question is: How can I check those caps for shorts? If they have to be removed for that I might as well replace them, at least the bigger ones.

Reply 1 of 6, by H3nrik V!

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I guess that if a tantalum was short, your power supply would shut down and the CPU not getting warm ..

If it's dual it's kind of cool ... 😎

--- GA586DX --- P2B-DS --- BP6 ---

Please use the "quote" option if asking questions to what I write - it will really up the chances of me noticing 😀

Reply 2 of 6, by MikeSG

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With the power on, if the voltage is less than ~4.9V then the board could benefit from replacing the tantalums. Caps around the power supply connector & battery.

Also reseating ICs, especially cache chips W24257AK-15.

Reply 3 of 6, by Deunan

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Kouwes wrote on 2024-07-31, 07:54:

However, the board refuses to POST. My analyzer shows no activity but the CPU gets hot.

What's this grey/greenish stuff on the 74F08, between cache and the chipset? Just dust or corrosion?

And I have the same advice I just gave in another 367C mobo thread - there is a mounting hole on the PCB, behind the 8-bit ISA slot and next to 206 chip. It's very close to some important traces, make sure none of these were damaged when the mobo was installed or removed from the case. If you end up using this hole to support the mobo use nylon or paper washers even for plastic pegs.

Re-seat the BIOS chip. Remove x87 for testing, one less thing to worry about. Make sure your RAM sticks are in bank 0.

Reply 4 of 6, by Kouwes

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Thanks for the advice guys, much appreciated!
@Deunan: that’s weird shading on the picture, check the detail I attached.
I already removed the NPU but haven’t time to do more work yet.

Reply 5 of 6, by Kouwes

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Ok, here’s an update:
I removed all the chips that are socketed. CPU, NPU, cache, tag ram and bios.
Gave the sockets a good spray of deoxid and that did the trick! Board is now posting like a champ.

Another nice board saved. I put 8MB, an Oak video card and a sound blaster 2.0 in it.

Reply 6 of 6, by Thermalwrong

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Kouwes wrote on 2024-08-06, 05:29:
Ok, here’s an update: I removed all the chips that are socketed. CPU, NPU, cache, tag ram and bios. Gave the sockets a good spra […]
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Ok, here’s an update:
I removed all the chips that are socketed. CPU, NPU, cache, tag ram and bios.
Gave the sockets a good spray of deoxid and that did the trick! Board is now posting like a champ.

Another nice board saved. I put 8MB, an Oak video card and a sound blaster 2.0 in it.

Congrats 😀 I thought that thing looked too clean and uncorroded to be a dead board. Nice little setup.

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