NMB RT101+ Key Issues

[DrunkUkrainian]

I recently bought an RT101+ on eBay for a good price, but the tab, 1, q, a, and z keys don't actuate reliably. Sometimes they don't sometimes they do (especially if I mash them), and sometimes they chatter. Does anyone know how to fix this? I know very little about circuit diagrams but if someone has one for this keyboard it would at least be a start. Thank you!

[XMIT]

There really isn’t much to a Space Invaders switch. It’s two little gold plated prongs that make contact. I would suspect the contacts are dirty.

[Jesseg]

I recently bought an RT101+ on eBay for a good price, but the tab, 1, q, a, and z keys don't actuate reliably. Sometimes they don't sometimes they do (especially if I mash them), and sometimes they chatter. Does anyone know how to fix this? I know very little about circuit diagrams but if someone has one for this keyboard it would at least be a start. Thank you!

I imagine those specific keys would share the same column on the switch matrix, check before 1

[SK-8K]

Isn't the RT101 a rubber dome? If so try cleaning the membranes.

[DrunkUkrainian]

I imagine those specific keys would share the same column on the switch matrix, check before 1

If you mean the ~ key, that one does work. Actually, I took it apart to test the continuity to see if it was something obvious and they seem to have gotten much better. If you have any advice for a more legit repair I would greatly appreciate it but it seems to be working fine for now.

[DrunkUkrainian]

And as soon as I say that and shut the case it starts acting up again.

[Muirium]

Good curse.

Sounds like a controller / matrix issue as it's affecting several closely linked keys. Actually tracking it down may be complex.

[Palatino]

I have a new old stock split spacebar NMB keyboard with a similar issue - loads of dead keys - so it looks like these boards are prone to controller/matrix issues (though I’ve had none on my inozenz stock) rather than dirty contacts. I mean to open it up some time - I’ll let you know what I find.

[Muirium]

Share some good pics of the PCB and I'll have a go at working out the matrix: specifically the broken part. A little hobby within a hobby of mine.

[DrunkUkrainian]

Share some good pics of the PCB and I'll have a go at working out the matrix: specifically the broken part. A little hobby within a hobby of mine.

https://imgur.com/a/ywWNteC
Here is an Imgur link with the full PCB, a closeup of the problematic section and a duplicate with marks next to the problem switches. If you need any more pictures or for me to test continuity, feel free to ask here or on Discord (DrunkUkrainian#0001). I really appreciate your help

Having taken it apart again, it works almost perfectly when I am pressing on the contacts of the switch S40, but when I bridge them with metal it activates the switch.

[Polecat]

That's exactly what we needed. The problem column splits off after the ~ switch (S17), and all the switches after it in that column are not working, so if the ~ key is working correctly the problem will be either the solder connections on the right pins on that switch, the internal leaf which jumpers those two pins together, or one of the traces leading to or from one of those two terminals.

Do a continuity test on the traces leading to and from the right side pins on the ~ switch, and between the two right side pins on that switch, and you should find the problem.

[jsheradin]

Space invaders are a bit unique in the the switches are 4 pins with each pair internally connected (vertically). This makes routing easier but it also means that any single bad joint on one switch can take out a whole column/row.

Double check that there's continuity across all the pins on that column. Work your way back to the controller checking continuity at every jumper and along every trace.

With any luck it's just a cold joint that can be fixed with a quick touch of a soldering iron.

Edit: Polecat beat me to it, do what he said.

[DrunkUkrainian]

That's exactly what we needed. The problem column splits off after the ~ switch (S17), and all the switches after it in that column are not working, so if the ~ key is working correctly the problem will be either the solder connections on the right pins on that switch, the internal leaf which jumpers those two pins together, or one of the traces leading to or from one of those two terminals.

Do a continuity test on the traces leading to and from the right side pins on the ~ switch, and between the two right side pins on that switch, and you should find the problem.

If you mean testing continuity between the inputs of S17 and the inputs of the problem switches, it's all continuous, and pressing one of the problem switches makes the input of S17 continuous with all the outputs. Also not sure how my finger being on the contacts of S40 helps in that regard, but it certainly does help all the problem switches work

[jsheradin]

Are these two pins a dead short?

Spoiler:

s17.png (1.22 MiB) Viewed 4820 times

If not, try touching up the joints with a soldering iron or wiring a jumper between them.

[DrunkUkrainian]

Alright, so it is continuous but not everywhere, which might explain the issues. I'll try reflowing it tomorrow and update as soon as I do. Thank you for all your help so far!

[Polecat]

Flexing the PC board in the area of the bad connection can make it start or stop working. The solder connections on S17 are the most likely problem, but you could also have a cracked trace in that area. Not always easy to see, but the meter will tell you what's really happening.

[DrunkUkrainian]

Resoldered the input pins on S17 and the problem keys started working a lot better. For a while the tab and 1 keys were linked to each other but that issue seems to have resolved itself after some careful prodding! In fact, this message was typed on the keyboard. Thank you all for your help.

[Palatino]

Nice work. This gives me hope I can fix mine in the same way. I’m a terrible solderer, but now feeling bolderer.

[Polecat]

Is it just "...a lot better", or is it actually fixed? Hopefully the latter. Thanks for the update.

[DrunkUkrainian]

It definitely was a lot better before. It works well when first plugged in, so I tested it, thought it was good, and closed it back up. It deteriorated over a little gaming session so I opened it back up and fixed up the first job so now I just have to wait and see if it'll get worse again.

Edit: 24 hours later and it seems to be working fully! Yay!

[Polecat]

Edit: 24 hours later and it seems to be working fully! Yay!

Good job, glad to hear it!

[DrunkUkrainian]

Alright, I don't know what's going on but it always seems to deteriorate after a certain mount of time. I've wanted to get a desoldering gun for a while now, so maybe I'll get one soon and take the plate off to see what's going on. Thanks for the help guys.

[Polecat]

Alright, I don't know what's going on but it always seems to deteriorate after a certain mount of time. I've wanted to get a desoldering gun for a while now, so maybe I'll get one soon and take the plate off to see what's going on. Thanks for the help guys.

Before doing that try soldering jumper wires from the pads on the input side of S17 to the adjacent switches as jsheradin suggested. You most likely have a cracked trace next to one of the pads, and messing with it makes it work for a while until the two sides separate again. Very common problem on PC boards, especially those that get flexed or dropped. Bypassing the cracked spot with a jumper wire will give a permanent fix.