It's not really a surprise but after a couple of hours of usage, my M100 froze and was back being stuck on the menu... so I continued following the service manual troubleshooting instructions.
Philip Avery wrote: > I too had this problem of random date data & unresponsive keyboard, > albeit with a T102. It usually came right after being on 10mins, but > eventually didn't.? I found there was no Timing Pulse (TP) from the RTC. > This lead me to Chip Select (CS) which was open. It is fed by /RESET so > should have been hi. I had another T102 open at the time so checked > this. Tied CS to /RESET elsewhere & all good ever since. You're very close :o) I found a very low frequency signal on the TP. Something between 1.2 Hz and 4 Hz (but I'm not sure my multimeter is very accurate with very low frequencies). I hooked a very limited oscilloscope to confirm the reading, and after a few minutes, I have seen the frequency augment to 256 Hz (service manual says it should be 250 Hz... close enough). And it worked again... until this morning, and TP is now totally dead (low output, no oscillation) :o( Following Philip advice, I checked CS which was high (5.04V) so it's not exactly the same problem than his M102. I've seen on the clock diagram on the service manual than CS was fed into two AND gates, one with CLK and one with STB so I checked those too: CLK is pretty active (I guess someone is trying to talk to the RTC) and STB is almost always low, getting high for a few ms every now and then. I would like to check the oscillator inputs of the RTC but I have no idea how to do this with an oscilloscope and/or a multimeter. Fugu ME100 wrote: > The +5V looks good, the -5V is a bit low it would be better in the -4.9V > to -5.1V region. That should go up when the caps are replaced. I'll try to do this > It sounds like there is a bad joint somewhere on the board. That sounds like something not easy to find :o( > I think most Model T owners have more than one unit :-D Time to go back on eBay then ;o) but I still hope I'll be able to fix this one too. Also I noticed the TH1 Thermister looks very damaged (a whole side of coating is missing, and we can see the metal plate underneath). Could that be related? Eric
