Gregory's Serverthe 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.
 44 comments
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. @tubetime Thank you for sharing the plate picture. For some reason looking at them brings a feeling of comfort in me. On slightly related note since Factorio become mainstream I need to doublecheck plate photos. Some of them are really looks like a Factorio maps and other way around. 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) @tubetime Odd question but is it still possible to get replacements for those big red switches on the 5150 power supply? 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. my guess is that it is the system board memory that has gone bad. funny coincidence, i'm designing a memory tester right now! however, i hadn't thought about putting in sockets for these little guys. can you even *get* sockets?  @tubetime What kind of packaging is that? I’ve never seen anything like it. @foobarsoft IBM's crazy odd MST modules (later versions of their SLT modules that they invented in the 1960s) @tubetime Because of my unique personal history, my first thought was "I wonder if those were made in Burlington" (which was actually Essex Junction). @wollman see where it says "IBM 14" in the middle? the number there indicates the factory it was made in. apparently the code 29 indicated Essex, so this was a different factory. (see https://www.righto.com/2021/01/) https://www.twitch.tv/tubetimeus let's do some more board layout -- this time, i'm cloning an IBM PS/2 model 80 memory card (gee i wonder why) some folks are wondering what those metal cans are in the other post. here's a handy reference chart from IBM that shows modules with the lids removed.  @tubetime Yet Another Weird IBM Package I guess. All part of its early days vertical integration and vendor lock in strategy? @EricCarroll IBM MST. based on an earlier tech they called SLT (solid logic technology) that they developed in the '60s. @tubetime I thought it looked like the SLT package from the IBM 1130 & 370 I had my hands on at one time. Never seen MST before. Thanks!  |
looks like it might be the power switch. I'm expecting less resistance than this.