Model F XT working intermittently, converter working, internal PCB problem?

[gumilarganjar]

Has anyone had any experience with intermittent IBM model F XT connection? I had problems with the PCB connector but failed to recognize any hardware issues (no bent pin, no bad PCB traces, no rust). Overall, the keyboard is clean.

Strangely, the problems appear only at every attempt to connect and reconnect the keyboard to the host devices. Once it connected, it worked perfectly fine, with no issues whatsoever. But when it failed to connect, it didn't register any keypresses. The converter is detected, tested, and working with another XT (i have two). I tried changing the converter (teensies or pro micros) and tried different firmware (TMK and Soarer's), but the problem persists. I think it's not on the software side.

So far, my only chance is to keep replugging all connections and sockets (the 7x2P Dupont / jumper to the converter and the converter to the computer). The solution worked quite predictably last week, but now, I had to replug gazillion times to make it work. But the failure remains increasingly frequent, to the point of no longer functioning.

Should I consult a technician to diagnose the problem further? Any insights would be appreciated; thanks.

[Maledicted]

The most important thing with F XTs is grounding. Make sure the screw holding the plate sandwich to the PCB is tight and that the ground strap is in place against the bottom of the case when you reassemble. It is held there with one of the case screws.

[gumilarganjar]

Okay, I’ll check the hex screw asap. However, I am using internal converter directly connected to the controller via the 10P IDC, additional grounding wire is unfortunately severed by the previous owner. Any tips to properly ground using this method?

[Maledicted]

You could try a ring terminal wired to a spare ground pin on the converter. The Pro Micro has a few of them. I know the original ground strap is wired to the shield on the original 5-pin din so that should be pretty much the same.

[gumilarganjar]

ah i see, thanks for the tips. since promicro / teensy has 2 grounding pins, so i can use the spare one as additional ground?

[Maledicted]

I have wired the shield of a 5-pin din connector directly to the spare ground on a pro micro in my main Soarer's/TMK converter with no ill effects. The shield is normally grounded anyway, and that's the modern equivalent of doing so with a converter.

[gumilarganjar]

Good news, my keyboard is working again, without any issues, and yes, I guess the problem lies in the grounding of the keyboard. I properly cleaned my keyboard using contact cleaner (previously, I used only alcohol), paid extra attention to the grounding bolt and pads, tightened it securely, and now it works again. I hope there will be no more issues in the future.

Thanks for the insight!

[Maledicted]

Great news. I'm glad to hear it. Enjoy your F XT.