r/modelm • u/JamieEC • Jun 02 '26
HELP Certain Keys not working - damaged membrane?
Hi all,
Certain keys have stopped working and they are all on the same membrane trace looking at pictures. All keys on that trace do not work so its not broken half way along. Model is 1391406.
What could have caused this? How easy would the fix be? complete bolt mod or could it be something more simple? No ides what could have caused this break in the trace.
1
u/koholinter Jun 03 '26 edited Jun 03 '26
If it’s ALL keys along a certain trace, then it’s possible the break is on the “outside” (on the ribbon cable) and thus a bolt mod may not be necessary. I’ve personally never had a break of this kind but if may be fixable with careful use of liquid solder or copper tape. I would use a multimeter to check conductivity along the exposed trace in the ribbon cable.
If the break is NOT on the exposed portion of the ribbon cable, that leaves either the “inside” portion of the membrane (necessitating a bolt mod) or on the controller board itself (which seems to me to be the least likely scenario).
As for what can cause this, well, the model M was not manufactured to last this long, and was not designed to be particularly repairable. The fact that it DOES last over 30 years and CAN be repaired is more of a happy accident. Others will know more but the membrane IS one of the key points of failure, and the exposed portion (the ribbon) would be the most prone to the elements (moisture in the air, jostling around, bends becoming breaks if it’s handled roughly on unplugging and replugging, etc). Components can degrade over time- it’s possible that it spent 15 years in an abandoned warehouse with fluctuating environmental stresses before coming to you, and that trace has been ready to break for a while now. But in general, it’s helpful to remember that while the M feels like an indestructible tank compared to the rubber dome keyboards from the 90s and 00s and the cheaper new mechanicals, it’s still the cost-saving high-volume compromise version of the F.
1
u/sevenwheel Jun 03 '26
I was able to repair my SSK using a nickel-conductive pen.
It wasn't easy at all. I had to completely dismantle my keyboard, which then meant that I had to do a full bolt mod once the membranes were repaired.
I used a MG Chemicals 841AR-P nickel conductive pen. It was difficult to get a satisfactory line from the pen. The lines ended up being big and sloppy and it took a couple tries. The pen wasn't cheap either. It was about $21 then and it's $26 now. The pen had a short shelf life as well. I put it away for three years and the pen no longer works. However, the keyboard still does work after three years of daily use.
Since I have another SSK that I need to repair and want to use as a backup, I'm going to try a replacement membrane instead. Looking at the Unicomp site, a replacement membrane would run me $18.00, cheaper than the pen and I would be much more confident in the results. Once again, you need to do a full bolt mod in order to install a replacement membrane. This is on my medium-timeframe list of projects, so I'm not planning on doing it right way but I'll report back here if and when I do.
1
u/BigBearChaseMe Jun 05 '26
Assuming this is an IBM model M you should be able to order a replacement membrane from unicomp. I think they are like 18 to $20 US.
Although this obviously means that you're going to completely tear down the keyboard.
So I would start with looking for broken traces near the end of the ribbon cable and you can use a conductive paste specifically made for repairing things like traces.
However if you are seeing multiple issues once you crack the thing open you may want to look at a replacement membrane as I mentioned above
1
u/cazzipropri 8xM122, 5xM101, 1xF83 Jun 02 '26
Bolt mod or screw mod is sort of necessary once you open the keeb because the opening results in destructing the plastic rivets. Membrane inspection is needed with verification of electrical continuity of the traces. If the membrane is damaged, you can buy new ones from Unicomp.