Help Troubleshooting IBM Model M issue

[pws328]

Hey guys, thanks in advance for any help with this! It's been driving me nuts!

Here's the issue - When my model M is plugged into the PS2 port, my computer hangs at the bios screen. Nothing appears onscreen, and it just freezes. I've tried this on multiple computers (each on the PS2 port) and each PC exhibits the same behavior. If I let the computer boot into the bios, THEN plug the keyboard in, it works perfectly. Both in the bios, and in windows.

Backstory. So in a wave of nostalgia, I picked up an IBM Model M (model 1391401) and for a week or so it worked great on my main rig at home. I had it plugged into the PS2 port and there were no weird key issues or problems at all. Noting indicating a bad board. So one day I sit down at my desk (with the computer off). Moving some stuff around, I hit the ESC key, and my computer fires up, but doesn't boot. Now in the bios, I had only set the spacebar to allow the keyboard to turn on the computer, so I thought that was weird. And that's when the issue started. I've tested the M on three computers at home, and one at my office, all with the same result. Won't boot with KB plugged in, will boot, and keyboard will work if plugged in post boot. When the M is plugged in and the computer starts to boot, the lights on the board will flash, but won't stay on or toggle when pressed.

Could I have fried the controller somehow by starting the computer with the ESC key? But if it's fried, why does it work if I plug it in at the bios splash screen? I've googled everything I can think of to fix this issue, and have come up with nothing.

I'm waiting on my 7/32 driver to crack this thing open to see if I have visible controller damage, but until then, I'd greatly appreciate any guidance on this.

[Snowdog993]

You might have done what my nephew did.  I found nothing at all wrong with the keyboard.  I cleaned everything, and all the keys worked fine.  It would intermittently disconnect itself and reconnect for no reason at all.  I overlooked the membrane that connected to the controller.  It was a bit dirty, and it was causing havoc with the keyboard.  I cleaned it up, and reconnected the membrane and he has had no problem after I fixed that.
You might (just might) have a blown capacitor in the controller.  That would need to be replaced if that is the problem.

[pws328]

Thanks for the reply! I'll definitely check out the cables from the membrane into the controller. Hopefully it's just a bad contact like you said, or maybe a blown cap.

[pws328]

Not sure if anyone is still following this, but figured I'd update in case anyone in the future has this issue.

I finally got my 7/32 driver in yesterday. I popped the case on the Model M, and everything looked good on the controller and membranes. No blown caps, no fried traces, nothing. Poked around for a little while with the multimeter to see if anything came up bad, and still nothing. I re-seated the ribbons from the membranes, and then not knowing what else to do, reassembled and tested.

And it worked! Computer booted up just fine with the keyboard plugged in, multiple times.

Not sure if I discharged a cap fully, or if one of the traces wasn't seated correctly, or what the issue is, but it works now, and I can get back to clacking!

[CPTBadAss]

Hooray for easy fixes!

[fohat.digs]

Hooray for easy fixes!

I have had many times where unplugging everything and putting it back together securely did the trick.

Also, considering the hopeless snake nest of cables around my computer area, I have at least one cable go bad every 2-5 years and it is often one of the last things I check.

[rowdy]

Thank you for posting the followup, and congratulations on resolving the situation, even if you're not sure what you did to actually fix it.

I'd also vote for the "unplug and replug" action that probably fixed it.  Always worth a try with the older electronics.