Model F122 Column Issue

[Lucid]

I have an F122 that I'm restoring. I have everything pretty much completed. Everything is reassembled and tested. Everything works perfectly (I'm actually typing this post on it) except for an entire column of keys. The column I am referring to is this one:



It includes Home, Page Up, Page Down, Numdad 7, Numpad 4, Numpad 1, and Left Arrow.

None of the keys in this column register at all. I am using Soarer's converter and HID listen, and this is the only column that is not sending scan codes.

It looks like this column is connected to the 5th closest pin of the ribbon cable to the main pin header on the controller board. I ohm'ed out the connection from the main PCB to the controller board, and from the pin on the controller board all the way to an IC. No issues.

Any thoughts on what could be causing this? I'm hoping that it isn't a problem with the main PCB itself. Would really love to not have to take this thing apart AGAIN.

[Fkazim]

The problem could be where the ribbon cable connects to the pcb. Have you done a continuity test from the ribbon cable to one of the pads on the bad column?

[Lucid]

The problem could be where the ribbon cable connects to the pcb. Have you done a continuity test from the ribbon cable to one of the pads on the bad column?

That's a good question. I performed a continuity test from the ribbon cable solder joint on the main PCB to the corresponding solder joint on the controller board and everything checked out fine. I haven't checked the continuity from the ribbon cable solder joint on the main PCB to one of the capsense pads on the bad column. I would have to take everything apart again (for the fourth time, I think, because of errors during re-assembly) to check that.

It looks like I can get a probe to part of the trace going to the solder joint from the bad column to check it without having to rip the whole thing apart. If that doesn't work, I'm pretty sure I'm going to have to take everything apart again to check for physical damage on the PCB.

The weird thing is that a bad column seems to point to a bad trace on the backside of the main PCB, but I never took the main PCB apart from the curved back plate. Which makes me wonder how damage could occur there. Not saying it couldn't happen (e.g., from the previous owner messing with it or just general bad abuse).

[fohat]

take everything apart again (for the fourth time

I never took the main PCB apart from the curved back plate.

I have been through the process many times (dozens) and 4 attempts is not cause for distress. I may not have ever gotten it perfect on the first go, and these days after 4 is probably where I would start becoming "seriously irritated" ....

Sliding the PCB on and off the metal plate is extremely easy, and might be worth a wipe, although I agree that it is unlikely that there is a problem in there.

[Lucid]

I will say that after the 4th time reassembling the thing, I have my clamp technique down. Probably took me 45 seconds to get all the clamps on and to push the back plate and barrel plate together.

One thing I noticed when trying to check continuity between the ribbon cable solder joint and the trace associated with the column is that the ribbon cable solder joint is shorted to the back plate. I assume that is not normal. None of the other ribbon cable solder joints are. I will dig in to this.

[Lucid]

So I took the thing apart again and took the PCB off of the back plate. No signs of visible damage, but then again I may not have the best eye for what to look for.

I did notice that in this restoration video: https://youtu.be/Zl7AMp7Cffs?t=1393 at the 23:00 minute mark, there is a plastic dielectric sheet between the back of the main PCB and the back plate. Mine does not have that. Although there are some slight differences between that F122 and mine, I wonder if mine would benefit from adding something like that.

[Lucid]

So after taking the PCB off the back plate, I put some Kapton tape on the back of the PCB along the capsense pads and the trace of the column in question all the way to the ribbon cable. Just reassembled it and tried the keys and it all works now. There we go.

[Fkazim]

Glad it all worked out in the end enjoy that keyboard

[Wazrach]

I carry out bolt-mods on my F122s and isolate them from the backplate using electrical tape. I didn't know this in the past, so I'd end up with chattering or keys next to the bolts just not working.

[Lucid]

If anyone is interested, I posted a gallery of the full restoration process here:

viewtopic.php?f=62&t=26521