the power supply in my PS/2 model 80 stopped working, so it's time to remove it and fix it. three screws and it even has a nice little handle in the form of a zip tie.
looks like it might be the power switch. I'm expecting less resistance than this.
power switch tests good. sigh, I hate working on big AC power supplies
i'm having a lot of trouble getting the screws out (holding the board in place) so i think i'll take a break.
got the board out. the hex screw heads are a loose fit for 3/16 and 5mm but a very tight fit for 4.5mm.
https://www.twitch.tv/tubetimeus think I'll do a little reverse engineering stream. this should be fairly straightforward.
made a good amount of progress, but the control circuit is quite involved and has lots of discrete parts, so it's slow going at this point.
https://www.twitch.tv/tubetimeus
we're back on stream!
and the reverse engineering is basically done. it is missing a couple of capacitor values but you get a pretty good idea of how this thing works.
so the bias voltage rail isn't high enough. it hits about 9V and that is it. the supply checks it and won't power up until it hits 11.8V.
which means i probably have to dig into this tricky little circuit. this is a preregulator that chops the incoming AC voltage if it detects 220V. then it goes through a 120V->12V linear power supply circuit that is pretty normal.
burn mark on this capacitor is very sus. turns out it failed in a dead short!
this is the cap that failed. it basically shorted the bootstrap supply for the bootstrap supply (heheh)
also the computer works fine now. *phew* now what was i trying to do with it anyway? 🤔
oh yeah i was swapping out the Type 1 planar (16 MHz 386) for a Type 2 planar (20MHz 386).
well that works! this is the planar that had the cracked chip on it that I fixed (see the yellow labels in the previous photo).
the type 1 planar is on the left and the type 2 is on the right. i've got a Kingston 486 upgrade card in the one on the left.
after putting the Type 1 planar/motherboard back in, the computer failed AGAIN. this time with a black screen and no beeps. 😦
OK, i put my MC Mechanic POST card in it. this is a Micro Channel machine so you can't use an ordinary ISA POST card, which is why i designed this one. looks like it is running code!?
weirdly enough, it booted to the setup disk just fine, but during automatic configuration, the screen goes blank and the whole thing locks up. from then on, any cold power cycle results in the error code 0F! i've pulled the battery again to clear whatever was loaded in there.
OK i let it sit and then rewrote a new reference disk. perhaps it detected the type 2 planar and screwed something up in the type 1 planar's CMOS?
it runs now. i get a 201 error and a 164 error on boot. hmm, memory error and memory size error.
looks like I need to get my system unit serviced. error 10400 is pretty generic.
