Doctor, how far "M" I gone?

[HuBandiT]

I'm looking for info on how mendable and how "moddable" this Model M I was given is.

Mechanically it feels to be in perfect shape. So it feels like a waste to let it go unfixed and unused. Plus it's sturdy and spacious case looks like a good candidate for modernization projects.

Mending:

The narrower foil connector film strip is trimmed back - incomplete mending efforts of the previous owner:

unfinished job

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narrow one is trimmed back

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Is there a way to fix this? I'm reasonable with a soldering iron and bits in computers, not that great on dexterity/mechanical stuff/manual labour.

(I would like to replace the controller board with a custom one, if that matters.)

Modding:

Is there a way to replace the foil 2KRO sandwich with something better? E.g. replace with a PCB for capacitive sensing to turn it into an NKRO keyboard? (Oh wait, isn't that what the Model MF is... there I go thinking I had an original idea...)

Teaser:

no label on bottom

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top looks complete

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mold No on inside of top cover

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controller board - lovely 80s colors and arrangement; the transparent case 4 MHz crystal is not something often seen anymore

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top of assembly seems in good shape (all keys work well mechanically)

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close up of number on top of assembly

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bottom of assembly with ID labels (looks good - damn, they used AODN fasteners...)

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close up of bigger label on assembly bottom

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close up of smaller label on assembly bottom

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[Darkshado]

Worst case you could do a "bolt mod" (or "screw mod") and put in a new matrix sheet, besides, the board has a few broken "rivets" already.

Otherwise, I'm not sure how you'd go about repairing the 8 trace connector since the former owner removed the connector on the controller and replaced it with this 8 strand wire. I doubt the matrix would withstand much heat, so conductive ink or glue might be an option...

It's missing the LED indicators, which would be typical of terminal boards, though the keycaps don't have any unusual legends or the two 1u keys in place of the numpad +. I wonder if it speaks AT or XT.

[emdude]

Another option would be to bridge the traces and wires with copper tape. It would be less invasive, since you would not need to perform a bolt mod.

Something like this perhaps?



From khirin's Unicomp SSK mod: keyboards-f2/unicomp-ssk-from-ultra-cla ... 15238.html

It's missing the LED indicators, which would be typical of terminal boards, though the keycaps don't have any unusual legends or the two 1u keys in place of the numpad +. I wonder if it speaks AT or XT.

It looks like it could be the ISO version of the 1390120.

[micrex22]

It's missing the LED indicators, which would be typical of terminal boards, though the keycaps don't have any unusual legends or the two 1u keys in place of the numpad +. I wonder if it speaks AT or XT.

Not all terminal Model Ms omitted the LEDs. For instance Model M 1390120 can operate on the XT bus which is why the LEDs were omitted, since the XT doesn't use them. It can run on AT / PS/2 as well though.

Terminal Model Ms typically have a modified numpad and of course feature a different controller.

The 4 pin LED header is still present on the controller in that M, and you could solder a cable with the corresponding LEDs to it. The resistors are conveniently located on the PCB so you don't need to run any of those.

[Arakula]

The key caps are from a standard German 1391403, just slightly randomized .
The controller board also looks like a normal PS/2 one (got the LED cable connector), not a terminal.
I think this keyboard belonged to an IBM PC/XT.

I don't know why the previous owner did what he did, but it seems he didn't really think it through before he started, then lost interest in finishing what suddenly turned out to be far more complicated than he thought (see the soldering iron burn marks on what's left of the flat cable).

Apart from getting a new set of foils from Unicomp and doing a complete bolt mod (best, although expensive way, if you're located in Hungary), I think your best bet would be to go the copper foil route, if you can find an area where the traces on the foil are not covered. For that, a bolt mod might be necessary anyway.

Unless you really threw your heart at the project, I'd treat this thing as an organ donor, to stay in the "Doctor" language. Obtaining a working Model M is far less time-consuming and possibly also cheaper than repairing this one.

[HuBandiT]

Thanks guys!

emdude,

That not-having-to-open-it sounds tempting (impressive down-sized keyboard in that thread too!), however I wouldn't know how to get good access the conductive metal layer beneath the external plastic layers without damaging it. Does one just scratch away the top layer with a knifepoint or something? sand it away with sandpaper? Use some kind of abrasive tool? Nah, I'm pretty clueless at these things.

Darkshado,

If I decide to jump into making this guy work, I plan to replace the controller anyway, so that a connector is missing from the original controller board is not a problem in itself. Now it indeed will be an interesting question how to graft an electrical connection between this trimmed back foil connector and the future controller.

Missing LEDs are good for my modding purposes.

Do you want me to try to find out for you whether it speaks XT or AT even outside of the current context of mending (e.g. for historical purposes)?

micrex22,

Thanks, will take a look eventually! I'll try to see first whether I can get to a point where I can make the matrix work though. Although it might end up getting a graphic display instead in that currently conveniently blank indicator area.

Arakula,

Yes, exactly what I thought, they started at the part they knew how to do (the PCB) - and then they realized they don't know how to cope with the soldering-iron-incompatible foil.

All that can be accessed from the outside you can see in the above photos - I don't think there is a conductor exposed anywhere that is currently accessible (as in without a bolt mod).

Organ donor - well, yes, I'm definitely considering that. I'm also reading up on the Model MF thread, to see whether that might be something to consider. The actual reason I took out this IBM and looked at it was to create a capsense controller anyway (before realizing this actually is a foil-based resistive switch keyboard).

BTW are any of you M guys interested in NKRO for the M?

[Arakula]

BTW are any of you M guys interested in NKRO for the M?

Definitely. Slight PITA each time I use it as a little substitute for a musical keyboard.

[alh84001]

There is a thread dedicated to model M membrane repair workshop-f7/does-anyone-has-a-suggestio ... t9072.html

I had two model Ms that had a broken line in the ribbon cable part of the membrane. To access the signal line I had to use the box knife _very_ gently to expose it. One painful point might be checking for continuity to see if you actually exposed the contact or check that you hadn't scraped too much, which is easy when you have everything disassembled as lines on the membrane itself are exposed. You could then extend the copper tape from that point to the end of the cable, and then solder a wire there, similar to what was done in that Unicomp SSK mod.

To keep things simple, you should probably do a screw mod and change the membrane (I'm sure someone here has an extra that they don't need). It's relatively simple, but if you haven't done it before, it pays to have a practice run on a mutt board.