deskthority

Hey, guys. I have a Unicomp Model M that I got about a year ago. I took all the keys off to clean it the other day and replace a spring that was bent in shipping. I managed to replace the spring just fine (after much frustration, haha). However when I reassembled the keyboard, about 3 of the keys have become awfully scratchy, specifically Right arrow, Tab, and numpad multiply. None of these were the key with the spring I replaced. I've tried searching around online for a solution, but everything I can find talks about "plastic-on-plastic" scratching, but that's not what I'm experiencing. The scratch in my case is caused by metal rubbing against plastic, like the spring is rubbing against the slider or barrel.
I've tried everything I can think of to fix this. I've taken off the key and stuck it back on. I've pressed the keys a ton of times, I've replaced the spring (just taking it out and putting it back in and replacing it with a new one), and nothing has fixed this problem. It could just be my lack of skill in putting the springs back on correctly, but I've tried to replace it at least 8 times, so I'm not entirely convinced it's the way I'm installing the spring that's causing the problem.
One thing I did notice was that (especially on the right arrow) the spring seems to be angled differently. Most of the springs are centered in the barrel, while the right arrow's spring is angled more toward the top of the keyboard.
If you guys could offer any suggestions, I would be very appreciative. I really enjoy this site, I've been a lurker for quite a while, and I really like the boards here. Thank you!

Welcome to DT!

I don't really see how springs could get bent in shipping, anyhow you got that fixed, so moving along... [glares in the general direction of Unicomp's quality control.]

Spring alignment when inserting keycaps can sometimes be finicky, with incorrect placement leading to "crunchy" sounding and strange feeling presses. Try lifting the keyboard so the springs tilt forward a bit, insert the cap gently, 'til you feel a bit of resistance, then push it so the stem clips in the barrel plate. This should ensure the top of the spring is properly seated in the top of the stem.

Another thing to check are the stems themselves: if the notch on the back of the stem has leftover plastic from molding instead of a clean edge, that can interfere with the spring buckling; good news is that this can be easily cleaned off with a sharp blade.

Keep us updated, sincerely,

Darkshado

Alright, so I've done a little more investigating, and from what I can tell, the problem may indeed be coming from the stems. I took the right arrow and swapped it with the left arrow, and now it is the left arrow that is having the scratching problem. I have not yet attempted to fix them yet, as I'm scared of messing them up more, but at least I know now that it can be fixed. I honestly thought it was something wrong with the flipper and that I would have to take the entire case apart in order to fix my problem, and I don't know if I'm quite up to bolt modding the thing (that is, if you have to bolt mod an Unicomp Model M). If you have any tips on what I should be looking for while scraping that plastic, that would be appreciated. Thanks again.

I checked my stash of extra Unicomp caps and it turns out a few still had the molding defects I have in mind (flashing). Some "witness marks" where the mold separates are completely normal and you'll see them on correct stems, this isn't:
So the fix is simply to use one of these: To carefully remove the excess material and end up with something like this: Give this a look and let us know.

Darkshado

Alright. So I went through with it, and it seems to have worked great! I did take a little more off than I probably should have, but that doesn't seem to have affected it negatively. Now I'll go ahead and do the same to the other problem keys. Thank you very much for you help!

Excellent!

(I wouldn't worry about having removed too much material: some old batches of caps had a notch about twice as high with no notable difference in sound or operation, so there's some leeway here.)