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486 Soyo mb : no post

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First post, by smokingchip

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Hi,

I have got a soyo 025L2, and it does not post, at all. No beeps either. (note that I tested it without any RAM nor cache chip, only with and without a CPU)

An analyzer board shows only dashes.

I followed few advice found here and there:
- checked for shorts: none so far
- checked the clock on socket: none (or at least nothing relevant, the board is configured for DX4 100), which is a problem
- circuits seem fine (I checked under a cheap digital microscope)
- looking at any damages: none so far (except the battery that was removed)
- checked the caps: no shorts, all seem ok
- checked the crystals: the signals seem fine (~14.7MHz, and another one at ~32.3 KHz)
- checked the address lines: I see something quickly passing by Addr 01 (not sure it is relevant, but it's a clear signal anyway at boot)
- reset behaves appropriately: up at boot for a split sec and down then.
- nothing seem to get hot nor slightly warm (though I don't have a infrared camera to be sure)

No idea where to look then.

Note: I remember removing a burnt cache chip, the extra one, and it was actually in the wrong side. Could it be that it damaged something else?

Any idea on your side?
Thanks

Reply 1 of 4, by MikeSG

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Any broken circuit traces near the battery?

Is the voltage to the CPU correct?

Jumper info: https://theretroweb.com/motherboards/s/soyo-s … 5k-sy-025l#docs

Some boards need the socketed ICs reseated a few times, or the sockets cleaned with alcohol & toothbrush to have a good connection.

Most likely a burnt cache chip inserted the wrong way didn't damage anything else.

Reply 2 of 4, by smokingchip

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The battery was removed long ago, there are only a few traces of corrosion on the solder of a few components, but nothing major (not green, no visible damage and caps seem fine, resistors are still within their range also)

I tried cleaning all seats with isoprop alcohol as you advised, but no change.

Without a CPU, there is no voltage. With a CPU it's at 2V sharp. But that's below what it is configured for: it should be 3.45V.

Thanks for the doc! It seems that jumpers did not match the CPU at all! (it was all messed up, no idea why: I never moved any of these once I got the board) Quickly set the things properly, and now it beeps!

Reply 3 of 4, by smokingchip

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And it posts! stops at C1-6E, but I did not populate the ram, nor the cache nor have any vga card plugged in so it could be just any of this.

Reply 4 of 4, by smokingchip

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And it boots perfectly fine. No cache does not seem to be an issue which is good (need to get some now). Lots of fun in front of me. But first, need to get a heatsink.

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