VOGONS


Reply 20 of 21, by tony359

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little update

XTAL 2 is grounded - hence no signal. Not sure whether it's not supposed to be grounded but it is and could not find a shorted component so far.

I then did a little patchwork, lifted some of the VIA legs, connected XTAL1 to GND and XTAL2 to clock. It was not very good so the connections were bad but... it booted up! The speaker kept beeping as if I was holding a key but everything worked. I ran doom and it worked fine for several minutes.

So I did a better patch work with the VIA chip and... nothing. For the life of me I was unable to make it work again. Board refuses to boot.

And yes, if I plug the VIA chip on another board, it still works. If I plug the original KBC on the affected board, the board still boots up fine. 😁

I'll keep testing! 😀

My Youtube channel: https://www.youtube.com/channel/UCvxgGy-GkPY9RA9BcLTBaFQ

Reply 21 of 21, by tony359

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Question for the board: I've noticed that the data line of the KBC chip look very different on the affected MB than another one. On a working motherboard they look like usual: a mess of pulses. On the affected MB, there seem to be much less activity which slightly changes when using the keyboard.

When the keyboard crashes, the data lines change to a more "normal" behaviour, which is very weird.

Can I assume that the KBC shares the same ISA bus with all the other cards? I'm curious to see if there is a latch (buffer?) chip in between the CPU and the KBC chip to see if something happens to it and also to check the ISA data lines when the keyboard crashes.

With my very limited knowledge of electronics, could the fact that the KBC chip is getting "busier" data lines when the keyboard stops working mean that the latch of the KBC chip is malfunctioning and "opening" to the whole bus to the chip? This is assuming that there is a latch between the KBC chip and the bus. Apologies if I am saying rubbish here!

My Youtube channel: https://www.youtube.com/channel/UCvxgGy-GkPY9RA9BcLTBaFQ