The Experience of Repairing a IBM Model M 1391401
Technology Keyboard PersonalI bought an IBM Model M about a year and a half ago. I found it on Facebook Marketplace while looking for a CRT monitor for a 90s computer I had just purchased. I went to pick up my monitor from Boyertown, PA, where a daughter and her father owned a trailer park filled with old electronics and collectibles. These were truck trailers filled with a bunch of stuff. In one of the trailers, I came across an old IBM Model M keyboard. There was also a Model F keyboard that looked like it controlled a spaceship, but the one that caught my eye was the classic 1391401. I asked how much it was, and they told me $70. I also ended up getting the CRT monitor. There’s a fun fact about those monitors—they were used in an elementary school in the 90s in that area! This was before school started up in Fall 2023, so I was pretty packed up. I ended up not really touching the keyboard due to the schedule changes and new school. However, when I did plug it in, I noticed that some keys did not work, like the Enter key and so on.
The Fall semester ended, and I decided to open up the keyboard to see what the problem was. It seemed like I was the first one to ever open it up due to all the debris and mess inside. I used a knife to cut off the plastic rivets that these keyboards use to hold the whole assembly together. Once the rivets were off, I was able to see the membrane and take off the metal plate and the plastic on top. I looked online to find out what to do next and realized that I was on my own. There is very little documentation on how to fix these keyboards, despite their iconic status. I jumped to the conclusion that the membrane was the problem since some keys were not registering, but all the spring assemblies were in great shape. I ended up purchasing a Unicomp 1391401 membrane.
Here’s some advice on how to test if your membrane works: use a multimeter on beep mode, hold one prong to the conductive ends and the other to a conductive circle where the lines follow. If it beeps, the key is registering. Some points won’t beep, but as long as they have some sort of signal, they are okay.
All the points I tested with the multimeter on my Unicomp membrane were beeping, so I replaced the old membrane with the new one. I also did the Model M Bolt Mod, so I bolted everything together. After assembling everything, not a single key was being registered! I took it apart and reassembled the keyboard a dozen times. I was confused because when I pressed the Num Lock key, the light would turn on, meaning the key was being pressed and registered, but none of the other keys worked. It was very frustrating. I kept taking it apart and trying something new each time to see if it would fix the problem. I thought the controller board might be messed up, but then I had the idea that there might be something wrong with the membrane I bought. I was skeptical but decided to try my original membrane again. This time, I bought a conductive ink pen and used it to draw the lines and circles on the membrane that were not receiving a signal with the multimeter. I tested each circle and line to make sure each point worked, and after about an hour, I was ready.
I put the keyboard back together loosely just to see if the keys worked, and it did! I then put everything back together and was so happy to have a fully functional and clean Model M.
Resources and Advice
To close out this post, I want to share some advice and resources for this process. The first piece of advice is to keep it simple. This is a very simple keyboard with primitive and easy-to-understand mechanics. Don’t jump to very deep conclusions because this is a straightforward keyboard to fix. This applies in general as well, especially with Linux problems and computers. Some problems are simple to fix, so don’t jump to a very complex answer. Keep it simple. Also, see if you can fix your membrane with a conductive ink pen instead of buying a new membrane that doesn’t work. Throwing money at parts never guarantees success. If you have any questions or comments for me, please email me. You can find my information below. Also, check out the resources that helped me with this project!