deskthority

Hello all, and Happy New Year, which is hopefully going better for your input gear than mine.

First off, my experience with keyboards is vast, 20+ years of handling, cleaning, refurbishing, retrobrighting, all different types, interfaces, layouts etc. I've rekeyed and cleaned model M and F keyboards in the past without any failure. Hell I've even upside-down shower-cleaned cheaper Mitsumi bubble wrap membrane keyboards. No failures.

Until now. On my flagship Model M, connected to my KVM that is hooked up to a half dozen retro rigs.

This one is completely baffling. I have an older (Lexmark) PS/2 Model M which I partially took apart to clean. Each keycap was lifted off and where special keys were integrated (Enter, Tab, spacebar), the entire key was removed so you can see the spring. All those keys were put into my bathroom sink and gently cleaned, rinsed as a whole, then spread out in a wide pan and let air dry overnight. They were 95% dry when put back together the next day, whatever little specks of water were left were blown out with a compressor before reattaching. I then took a vacuum cleaner with a soft brush to get the (three?) paperclips, fine coarse black hair, and other accounting dust (I know where this keyboard came from) out. I put back each key and connected it to my computer. I started typing in DOS and noticed that the N key also triggered the B key, but not in a way that I could issue the command CD BURNTIME (it would show up as BURBNTIME) so I just made a batch file and manually took out the extra B by backspacing.

Figured it was just a glitch.

Wrong.

By the time I tried to recall a game, or save it, half the keys were F**ked. I exited the game after assigning a usable filename and wow, the whole home and bottom row are completely shot. Press D, DF appears. Press F, FV appears. Press V,VF appears (same goes for pressing F, G AND M) Pressing Space activates the \ character and crlf (enter). 1 in the number pad activates/deactivates NUM LOCK. Half the keys in the number pad issue two or more characters when pressed. None of these are random and each sequence is reproducible on various hardware (from a 386 to a "modern" 2011 Xeon) - All of them pass the keyboard during POST, even react to a held down key.

The only row that works is the top row and the numbers in the first row. ALT and CTRL seem to work.

I took the keyboard apart after modifying a 5.5m 1/4 inch socket (I ground it down) and after cleaning the contacts from the, um, keyboard mesh matrix (?) to the PCB (heavy oxidation) there is no change.

Have I f**ed up this keyboard by vacuuming it? I really like these things and I recently sold a spare on eBay so I know how much these are worth... Does anyone have a busted one (outer case, torn wire, what have you) in case I really have killed this? How do I check it? Is there a schematic? I tried to see what was under the metal cover but it seems the plate is melted on.

I thought these keyboards were durable? I'd love to know exactly how I managed to do this....

If you have all the caps I can help you out.

I have a 9.7/10 cosmetic condition case, wire, and keys.

Just the innards are causing these problems. I just tried on another 386SX - same problem.

What do you have in mind?

Jed118 wrote: it seems the plate is melted on.

That is correct! The "barrel plate" on Model M boards is fixed to the metal backplate using so-called "plastic rivets", protruding pins are heated and pressed on as part of the manufacturing process.

Did you connect directly or with the KVM while you were testing? Just to rule that out.

It could be something with the matrix if some water did get in. To confirm, there should be scans or photos matching your exact model somewhere here which would help determine if this fits your reported symptoms. A "bolt mod" would enable matrix repair or replacement. (I haven't had to do one myself yet.)

It could be something that happened to fail on the controller at that moment. (Static discharge in dry winter air?) As you've seen by now, the controller itself can be swapped out fairly easily; check if anyone local to you has a "same-generation" M to try that. If it's a defective capacitor and you know how to solder, it should be an easy fix. Cindy (elecplus) might have some spares, otherwise Unicomp should.

Good luck,

Darkshado

Another thing to bear in mind, unicomp sell replacement parts (including new membranes) so it will always be repairable.

“Always” ends when Unicomp ends. Which I surely would not equate with infinity! They’re still with us, but I’ve long reckoned they’re only in business until the current, still original, staff retire. They certainly don’t give off the impression of a thriving manufacturer in this for the long haul; theirs is mostly behind them.

Thanks guys! I will look into this "bolt mod" and check the capacitor on the PCB.

The keyboard was tested directly to a few computers with PS/2 ports (and one through a DIN adapter) and it behaves the same way on each computer.

Is there a section in the forums for schematics? If I can get the backing plate off I am not averse to taking a multimeter to it

Here's the board - there are a couple electrolytic (which I might even have correct replacements for) and some tantalum caps. Which ones, from this board's experience, tend to go first? Logic dictates the electrolytics, but it seems odd behaviour for a cap to do that.



Anyways, I'm not an expert so I'll search for and read up on this "bolt mod" and at least educate myself in that direction.

Thank you for the pointers!

Given it was likely water damage, why not pull all the caps off and leave the board a few days and nights to dry out? Then see if anything has changed.

A bolt mod is open heart surgery, as far as Model Ms are concerned. The option of last resort. A lot of work, but if it needs it, it needs it. Best to explore other options first.

As for capacitors: yes, the electrolytics. Those things always go bad someday. They fail as a natural consequence of their construction. They were never intended for decades of use; in keyboards, motherboards or the many other places they show up.

It's a little surprising that after years of keyboard work you have never bolt-modded a Model M. For some (many) of us, speaking for myself in particular, that is the first major project that we undertake.

The first time or 2 is intimidating, but after that it becomes pretty much routine, although it is always fussy and time-consuming. A "screw repair" (where you don't separate and clean the internal layers) is really almost trivial.

I've never had a defective F or M before These things seem almost indestructible.

After pulling apart a friend's Model M (Dell version) and swapping out controller boards, my Model M acted the same way. Seems it is the keyboard itself

Depending on cost, I might buy a second hand keyboard and swap the parts in - I just had a new addition to the family and I do not have the time to mess around with opening the keyboard up just now.

Thanks for the help!

High time you tackled a bolt-mod.

Strip it completely apart and dust off / wipe down / and/or scrub with soapy water each individual part and put it all back together using the sandy55 method.

Considerable work but that is the ultimate upgrade to a Model M.

PS - if you are really serious replace the original thick black rubber mat ("blanket") with a new thin white latex one from Unicomp

fohat wrote: 10 Jan 2019, 00:32 High time you tackled a bolt-mod.
Strip it completely apart and dust off / wipe down / and/or scrub with soapy water each individual part and put it all back together using the sandy55 method.
Considerable work but that is the ultimate upgrade to a Model M...

Sorry for your troubles! But for sure if no other obvious easy fix comes up, then for sure would suggest going for the bolt/screw mod as fohat suggested - if nothing else it will get you very familiar with the Model M. Model Ms are tough - I've bought a couple that literally turned out to be pieces thrown into a box - but they worked when reassembled. If the membrane is truly ruined you can get replacements for them for a reasonable price from Unicomp -. I've done this with good results. (I love Unicomp no matter what anyone else says). Good luck!