Model M Chattering

[lhutton]

I've got a 1986 Model M that is chattering on the E key. It's a very early version and the barrel plate was badly cracked so I replaced it with a new part from Unicomp. Tried replacing the spring on the E key and if anything that made it worse.

I did notice that the membrane seems to be glued to the back plate. I've never seen that before. It's one of the very early zinc coated thick plates, don't think I can get the membrane off without destroying it. Anyone else seen these chatter? At this point the membrane is the only part left to replace ....

[kbdfr]

Model M?
search.php?keywords=rivets&terms=all&au ... mit=Search

[lhutton]

Model M?
search.php?keywords=rivets&terms=all&au ... mit=Search

You would think that by saying I replaced the cracked barrel plate it would imply a bolt mod but apparently not so allow me to be more specific:

Yes, I know very well about the rivets and have bolt modded quite a few of these. First time I've encountered a glued membrane and a chattering. I could simply throw a new membrane at it but I would rather not destroy the old one just flat our part swapping if I can help it.

[daedalus]

FWIW, Unicomp sells new membranes, as well as new rubber mats.

If you have issues with keys failing and/or chattering, you can potentially repair yourself, but it sounds like this keyboard has been through a lot and replacing the membrane outright may be the best path forward.

[lhutton]

FWIW, Unicomp sells new membranes, as well as new rubber mats.

If you have issues with keys failing and/or chattering, you can potentially repair yourself, but it sounds like this keyboard has been through a lot and replacing the membrane outright may be the best path forward.

Yeah I've got a couple of new membranes but I have to mod them to work on this old of a board. The one's Unicomp sells now are for the newer boards with the lines for the lock lights integrated into the conductor layer. Just need to trim that off, was kind of hoping this board's membrane was salvageable. Usually I will pull the layers a part and clean in between them but this one is all one piece and stuck to the metal back plate. Never seen this before but I've never had an M this old either. It's one of the very first runs by the date on the back.

[Howard81]

I purchased an early style membrane from Unicomp late last year, you just have to give them the model number of the keyboard.

[fohat]

I would wonder whether someone spilled a sugar drink into it, and if I was going to give up anyway, I would protect the circuit boards as best I could and soak the rest in water for an hour. If it was something simple that might let you peel them apart.

[lhutton]

I would wonder whether someone spilled a sugar drink into it, and if I was going to give up anyway, I would protect the circuit boards as best I could and soak the rest in water for an hour. If it was something simple that might let you peel them apart.

The thought had crossed my mind as well but it's so evenly stuck down it really looks intentional. This is November 86 Model M according to the case stamp and the internal assembly doesn't have a date on it, but it looks to be a very early one. It had plastic/rubber tubes along the inside edge of the old barrel frame as well, something else I hadn't seen before.

I purchased an early style membrane from Unicomp late last year, you just have to give them the model number of the keyboard.

I think you have to supply the model number on their site, even with that I've only ever gotten the newer style membrane. It's not a huge deal to modify them for use with the old boards. You just have to be careful trimming those 4 lines off the sheet.

[clickykeyboards]

I have seen a good number of early model M keyboards.
https://clickykeyboards.com/product-cat ... ver-label/

The following are not unusual for 1985 and 1986 model M keyboards (1390120/1390131/1391401)

a) curved metal plates that are relatively thicker and have the shiny coating

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b) 3 rubber tubes underneath the barrel plate

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c) I have also seen a number of instances (~30-40 model M keyboards out of 3000) where the 2 conductive membrane layers and separation layer are not free-floating but appear to be adhesively attached to the underside of the curved metal plate. At first I thought that the plastic in the membrane layers had chemically-broken down after 30 years and fused to the metal surface, but after seeing it happen more than a few times now over 15 years, it appears that IBM used adhesive in the process of building model M keyboards. I think I also saw this on an IBM wheelwriter keyboard from the same time frame. After 1987, it is more common to find the conductive mylar layers to be free-floating and not adhesively attached to the underside of the metal plate.

[lhutton]

Yeah, I just figured these things were due to it being an earlier Model M. I've seen the thicker zinc (I think) coated plates in a couple with an 87 or 88 date in one the back of the case. But those could have and their assemblies swapped before I got them so who knows. Glad to know I wasn't going crazy with the glued down membrane. I'm guessing there's no way to safely get them apart for cleaning? I've got a new membrane that can go it in the assembly if not.

This is the oldest one I've had to take all the way apart for a bolt mod. What is the deal with those rubber tubes? Liquid exclusion? The new barrel plate I installed doesn't have the channels for them obviously. Also, I noticed the new barrel plate I got from Unicomp is flat, it flexes OK and holds once bolted into place but as you can imagine that makes reassembly of the internals rather difficult since the springs like to go everywhere. I'm guessing the in factory the plate gets moulded to the metal backer by heat when it's riveted. Anyway to make it do that as a DIY'er?