Which capacitors in particular did you replace? On Thu, Oct 15, 2020 at 2:21 AM Jim Anderson <[email protected]> wrote:
> Hi, > > My first M100 died on me about two years ago with a problem where the VEE > supply voltage is low (between -1.4 and -1.7 volts, instead of the expected > -5v). At the time I posted here and the best guesses centered around one > or more bad capacitors, particularly C85. I did get around to removing C85 > at the time and it did have a tiny amount of fuzzy crud on the bottom > around the leads. I put the whole thing aside and swapped in a motherboard > from another parts machine. > > Fast forward to this year, after continuously putting off ordering the > capacitors from digikey, I finally ordered several capacitor replacement > kits and nimh memory batteries from arcadeshopper and today sat down to > re-cap this motherboard. Well, it seems maybe I should have started with a > different machine because all I've done is blow a few hours and frustrate > myself. I checked after replacing C85 and VEE was still only -1.7 volts, > so I soldiered on in the vain hope that maybe another bad cap was at fault > - replaced all the caps and sure enough it was still only -1.7 volts when I > was done. :( > > VDD is correct (+4.97 volts) and the memory nimh is charging when power is > connected (voltage at the battery rises). I'm testing the motherboard > without the lcd or keyboard connected as I'm pretty sure it's supposed to > be able to make -5v on VEE without those components connected... > > I'm not really familiar with expected diode test values, but to give you > guys some additional info to go on (in case any of these are bad) I lifted > one end on each of D13, D14, and D15 to test them, measured 0.22, 0.73, and > 0.54 volts forward drop respectively and open circuit in reverse. I don't > know if those are appropriate values. I also checked R97 and it is 180 > ohms as expected. > > Help!!! I feel like I've been banging my head against the wall all > evening. > > > > > > > > jim > >
