Thread by @TubeTimeUS

i'm going to try something really crazy that probably won't work. this is the CPU board from my PS/2 model 95, and it doesn't work. 🧵

that's THIS machine, the IBM PS/2 model 95. i tried fixing it before to no avail.

https://twitter.com/TubeTimeUS/status/1206700570150490112

no matter what i tried, it always got stuck with this error message when i tried to boot off a floppy disk (the reference disk, in this case)

i "fixed" the problem last time by swapping out the CPU card (IBM called it the "processor complex"). this isn't really ideal and it's slower than the broken one.

https://twitter.com/TubeTimeUS/status/1227745748730576896

so it turns out my broken CPU card is affected by this IBM ECA (engineering change announcement). the symptoms are similar, but not the same (01291500 errors vs 01291300 errors)

the ECA includes a way to identify boards that are affected by calling out a rework wire. boards that have the rework aren't affected!

so i'm thinking...

what if i add the rework wire to my board? will it magically fix the problem?

first problem: the ECA doesn't call out exactly what pins the wire is connected to.

fortunately, someone provided me with a picture of their board--which HAS the rework! so now i can see what pins the wire connects to.

second problem: this picture shows that some traces have been cut. i can do this too, but i don't know if any more traces need to be cut. there's just no way to tell without closely inspecting the entire board.

but hey, might as well try it.

it's going under the knife now

and there's the rework!

here goes nothin

BIOS comes up, so that's a good sign.

now it wants the reference disk

welp, show's over folks. must be something else wrong with it.

the PS/2 isn't real happy about it either