> > I have made an interesting, but sad, discovery. I traced both the two apparently > shorted pins on the gate array to two pins on the Chips & Technologies 82C206 > Integrated Peripherals Controller. Checking the 82C206, I found lots of pins on > that chip appear shorted to ground. I fear the > 82C206 has failed badly. > > I suppose that, happily, it looks possible to procure replacements for this chip. I > am slightly puzzled by the packaging of this chip though. It is surface mounted > on my CPU board, but the packages available for this chip are PLCC which I > assumed required a PLCC socket. Can PLCC chips be surface mounted, or is it a > subtly different packaging that I would need? > > There is no obvious damage from battery leakage near this chip, it was close- > ish to the damage area but the leak didn't reach it, so I think the failure is > either due to other damaged bits causing it to fail, or just plain old age. Is there > anything I could have missed that might make me think it is faulty when it isn't? >
For the time being I have decided to take a look at the other spare board, which works less well in that it does not produce any kind of video output at all, but on the basis that the 82C206 seems to be OK, it might be easier to repair, and I can compare it to the other board before I try replacing the 82C206. I have noticed on this spare that there is something wrong with the monitor sensing circuit, which feeds the PVGA1A. On the spare there is no activity on this pin, while on the partially working board there is activity. I traced it back to the inputs to a comparator (LM339). This comparator is comparing the RGB outputs of an Inmos G176 to a reference voltage. The behaviour is different for the two boards. I noticed however that these RGB pins are also connected through an SMT component (x3, one per colour) to the RGB pins of the VGA connector. The SMT component has no markings and when tested with a multimeter appears to be shorted across the terminals. It is labelled "FEn" (n=1,2,3). Is this just some kind of fuse? If not what could it be? Regards Rob
