IBM Model F XT reassembly question

[ShawnMeg]

Hello everyone,

Does anyone know what this wired is for?  I disassembled my IBM Model F XT for some cleaning.  There is a thin black wire coming off the DIN cable (see first pic circled in red).  On the end of it is a small metal ring/washer with sort of a star shaped opening.  I apologize that the cable coils are blocking off the end of it, but I found another picture (second pic) that sort of resembles it.  When I reassembled the board, it was a ***** to put it all together and I thought that one of the bolts that holds the case together goes through that little washer.  Anyways, when I tested out the keyboard, it was behaving badly.  For example, on a MS Word document, all sorts of random behavior occurred, with dialog boxes opening.  I took some of the keycaps off, reassembled without the the bolt going through the washer.  I put the keys back on, and all is OK for now.  I just want to make sure I'm putting it back together properly.

[E TwentyNine]

The post screw on the left is supposed to go thru it.  Don't know why removing it from that would make things better.  In my experience the grounding wires don't usually have much effect.

[dorkvader]

Yeah that's the ground clip for the shield on the cable. I believe it screws to the PCB.

Note: grounding is vitally important on capacitive keyboards. This explains the behaviour.

Glad you got it working again!

In my experience the grounding wires don't usually have much effect.

This is usually true for contact and hall effect switches, but capacitive switches are completely different. For example, xwhatsit's controller will not even work unless the ground clip is properly attached.

[ShawnMeg]

The post screw on the left is supposed to go thru it.  Don't know why removing it from that would make things better.  In my experience the grounding wires don't usually have much effect.

Maybe some of the keycaps were not seated correctly, so that may have been a problem.  If I just leave it without the post screw going through it, would it be harmful to the keyboard?  I can try to reassemble it with the screw going thru, but it was tricky for me to get the case closed.

[dorkvader]

As long as it's working, I'd leave it for now and then mess with it the next tine you have the KB open for whatever reason.

If I understand it correctly, the ground clip is not currently attached? I do believe it's just the clip for the shield on the cable, so it shouldn't affect functionality too much.

[E TwentyNine]

In my experience the grounding wires don't usually have much effect.

This is usually true for contact and hall effect switches, but capacitive switches are completely different. For example, xwhatsit's controller will not even work unless the ground clip is properly attached.

Note that his is working better without it attached.

I've run XTs and ATs fine without the ground wire attached, without the case.  I suspect it might be more vulnerable to having a problem without it in the rare case, but that has not been my experience.

[dorkvader]

In my experience the grounding wires don't usually have much effect.

This is usually true for contact and hall effect switches, but capacitive switches are completely different. For example, xwhatsit's controller will not even work unless the ground clip is properly attached.

Note that his is working better without it attached.

I've run XTs and ATs fine without the ground wire attached, without the case.  I suspect it might be more vulnerable to having a problem without it in the rare case, but that has not been my experience.

Note that it's because the shield return is not attached and the grounding wire is.

Both of those keyboards will not operate at all without the ground wire. Also, in both cases, the plastic case / metal bottom pan have no electrical function of the keyboard.

I just got out my AT model F and opened the box and the case and measured it and the backplate is attached to the shield clip via a standoff (as it should be). The backplate is also attached to the electrical ground of the controller, so it can properly shield the capacitance from stray Electro Magnetic Interference.

If this were not the case (that is: if the backplate of the KB were not electrically tied to the electrical ground of the controller) there would be issues.

I bet if you disconnect the controller from the plate and disconnect the clip it won't work as well.

[ShawnMeg]

As long as it's working, I'd leave it for now and then mess with it the next tine you have the KB open for whatever reason.

If I understand it correctly, the ground clip is not currently attached? I do believe it's just the clip for the shield on the cable, so it shouldn't affect functionality too much.

Thanks.  I'm typing on it right now.  I'll leave it for now.

[ShawnMeg]

In my experience the grounding wires don't usually have much effect.

This is usually true for contact and hall effect switches, but capacitive switches are completely different. For example, xwhatsit's controller will not even work unless the ground clip is properly attached.

Note that his is working better without it attached

I've run XTs and ATs fine without the ground wire attached, without the case.  I suspect it might be more vulnerable to having a problem without it in the rare case, but that has not been my experience.

It's difficult to say if it's working because I reseated the keycaps better versus an issue with the wire.