Hi All,

I have a Socket 3 motherboard with the SIS496 chipset on it, due to an error of my own fault (dropped a screw onto it while powered) I damaged the southbridge sis497, seems I caused a short from 12V EEPROM to the chip. Anyway, that was 6 months ago and since I sourced another faulty sis496 motherboard that would post 1 out of 100 times if you were lucky, and then ran unstable (dram controller issues, etc). I plucked the chip off it and swapped it over which brought the machine back to life, had a play and then put the machine back into storage until I had more time.

Back to today, I pulled the PC out again to have some gaming fun, etc. and found that it wouldn't post, in fact it had the same fault the original faulty MB had, seems it was a fault in the chip I moved. After hours of verifying my soldering and all the signals I discovered the MSRW tri-state output if the donor 497 is blown and would float instead of get pulled to ground when it wanted to access the EEPROM (it's tied to the eeprom output enable). I measured the resistance from the pin to ground and found that instead of getting < 10 ohm as expected, I was seeing 18M ohm, and inspecting it on a DSO I could see that the output was changing state, but had almost no ability to sink current (open collector output).

Removing the 4.7K pullup resistor and experimenting with higher and higher value pull-ups I found that 30M ohm (ridiculous I know) would allow the system to reliably post, however the input (remember, it's tri-state) on this pin is still ruined and I can not make use of any 16-bit ISA functionality.

So I am hoping that someone out there has a dead/parts SiS 496 they would be willing to sell? Or even pluck the 497 from?
Failing that if anyone has a working sis496 based board at a reasonable price I would also be interested (not as a donor, but to swap with this faulty board).