IBM Model F Keyboard Stuck Key errors... fixable?

[Ozzuneoj]

So, I came into possession of a Model F 83 key keyboard a couple years ago when a business closed. It was in storage since 1984 in its original box. The box reads "defective 7-6-1984" in marker. Inside is a printout of a report regarding the keyboard being taken to a repair shop back in 84. They said "the electronics inside had probably failed" and that it'd cost almost $200 to fix it, so they just replaced it with an aftermarket keyboard.

Fast forward to today and I just repaired the motherboard on my first IBM 5150 (more on that in another thread soon!) and I'm really excited to get this system running. The keyboard is showing stuck key errors and it prevents "Basic" from loading properly when it is connected. The system will simply stop at various stages of the Basic screen loading (part way through words, etc.). Before basic starts to load I've gotten "3c 301", "05 301" and "01 301" errors so far. Mashing on the respective keys (thanks to a list of scancodes I found) before turning the system back on seemed at first to move the error to a different scancode but it has repeatedly given me "01 301" a few times now... it may go to another later.

So, what do you think? Bad cable? Bad component on the circuit board? Actual stuck keys?? Where should I start? When I opened it I did notice that the black tacky tape stuff is incredibly gooey and left black residue on my fingers when I touched it... but its hard to tell if this could actually get into the keys. I didn't take it apart that far. I didn't see any visibly damaged components, but I doubt enough goes on inside one of these for anything to burn\explode anyway.

I don't see any indication that anything was spilled on it and its in incredibly good shape. The cord even looks pretty solid to me... but that doesn't mean much.

Any suggestions?

Here is the keyboard I have:
http://www.clickykeyboards.com/index...id/0/id/571249

The box says IBM Personal Computer Keyboard 1501100.

The computer I'm using it on is a 64-256 with what appears to be the '82 bios (if I'm identifying it right), all memory banks full, an AMD 8088 and no expansion cards currently installed other than a Quadcolor I CGA card.

[mbbrutman]

I just went through a fairly extensive cleaning (and then repair) of a Model F.

There really isn't much that can go wrong inside of one. There is a circuit board which is cradled/bent to conform to a steel backing plate to give it the curve. The electronics are on that circuit board so there are no ribbon connectors to go bad. The electronics are fairly simple; the keyboard controller IC is probably not easy to replace without salvaging one from another keyboard.

It's possible that there is something foreign in the keyboard that is causing the capacitive circuitry to trigger. Dis-assembly and cleaning is a pain but it can be done.

[SpidersWeb]

I'd guess a rocker plate (probably the wrong word) has come loose but that's a guess rather than a diagnosis - just from working with my own Model F's. I had the same symptoms when the plate under my ESC key went a little off to the side.

I never finished mine, and should probably give it another crack.
Other members on here have removed the PCB from the rocker/key assembly, sorted stuff out, and successfully reassembled.

I'd start by checking the cable using a multimeter. The keyboard is easy enough to open - two flathead screws I think? or is it four?
Then check for dry joints. If there is any obvious faults - you certainly want to pick this up before you separate the PCB-key sandwich - but I do doubt it's the electronics.

[mbbrutman]

Some pictures so that you know what you are dealing with:

IBM_5150_Keyboard_internals_1.jpg

This is where the magic happens - the circuit board. You can see the areas where the capacitive sensing is done.

IBM_5150_Keyboard_internals_2.jpg

This is the backside of the assembly - the steel plate that holds the circuit board in place and gives it its curve. Notice the minimal electronics.

IBM_5150_Keyboard_barrel_frame_underside.jpg

This is the underside of the plastic "barrel frame". The keys pop into the other side and travel up and down in the barrels. This side is where the flip plates (below) sit and pivot. The springs poke through to the underside of the keys.

IBM_5150_Keyboard_flip_plate_and_spring.jpg

And this is a flip plate - there is one for each key. Wikipedia has an excellent animation that shows how the spring and flip plate interact: https://commons.wikimedia.org/wiki/F...tion-300ms.gif

[retrogear]

Is that crud or glue between the 2 small IC's ?

IBM_5150_kbd.jpg

Larry G

[Stone]

Is that crud or glue between the 2 small IC's ?



Larry G

Crud? Glue? Neither. The area you circled has about five components (mostly resistors) in it.

[retrogear]

yea, I see the components but it just looks like gray crap in the middle. probably my eyes ...

[mbbrutman]

Instead of speculating why not just wait for me to answer the question?

IBM_5150_Keyboard_internals_3.jpg

No crud at all ... just resistors. I would not have put a keyboard back together after an extensive cleaning and left an obvious problem in place ...

[Compgeke]

The problem here sounds to me like either the plate is somehow loose causing bad contact, somehow a liquid or something got in and is causing issues or just a bad controller in general. These work using capacitance rather than metal-on-metal contact so any foreign substance can trigger a keypress (even your fingers on the PCB). There's a nice disassembly guide on the 5155 board here: http://deskthority.net/keyboards-f2/...ard-t7644.html . The process is the same except a PC (XT) board has two screws to get it open rather than removing plastic stuff.

If there does turn out to be a PCB\controller problem these boards are dirt cheap. It's not hard to get one for $30-40 shipped, especially if you don't mind going through and cleaning yourself.

[Stone]

If there does turn out to be a PCB\controller problem these boards are dirt cheap.

Ya', if you want on that's listed as 'for parts only', or 'not working'. Suppose the failed part is the one you need? Then you're stuck with two keyboards that both need the same part!

[retrogear]

>I would not have put a keyboard back together after an extensive cleaning and left an obvious problem in place ...

Lost track of who the OP was ...

[Maverick1978]

I've an 84-key model F that needs new foam... keys hit and miss. Bits of the foam layer poke out from the metal plates, and that disentegrates. It's a future project.... love the feel of that board.

[Ozzuneoj]

Thanks so much for all the input! I've dismantled this keyboard down to the PCB with only the cable plugged in and I'm still getting random stuck key errors. Its too bad, this thing is spotless inside... its obviously been in its box for 32 years.

Any suggestions as to what to do from here? I just have the PCB laying on my desk with the cable plugged into it, so there's no chance of anything conductive touching the pads. Maybe this isn't a proper test?

If this does in fact mean that its a problem with the circuit board, I can't find any information about people trying to fix these. There are several disassembly pages online but nothing about actually fixing or replacing components and diagnosing problems. Basically, something is telling the computer that random keys are being held down, and it is causing the system to lock up while getting through POST. There are two small ICs, the large black Intel chip and a small silver square IBM chip. Is it possible that the electrolytic capacitors have gone out of spec and need replaced? I know that that happens with speakers\amplifiers of this age.

EDIT: I found a very detailed thread related to these keyboards here:
http://www.vintage-computer.com/vcfo...p/t-43923.html
... but it just kind of ends with no resolution sadly. There's also no mention of stuck keys, so... who knows.

I really don't want to spend $120 to get a working keyboard for this computer. Is there any alternative? Aftermarket keyboards that are more common? Adapters to use "newer" keyboards on a 5150?

[Stone]

Where in Pa. are you?

I've got several keyboards for a 5150.

[Chuck(G)]

I really don't want to spend $120 to get a working keyboard for this computer. Is there any alternative? Aftermarket keyboards that are more common? Adapters to use "newer" keyboards on a 5150?

Lots of people use the PS/2-to-XT converter described here. If I had to do it today, I'll probably use a Chinese Maple Mini clone to do the heavy lifting. (How times have changed--the Mimi has several times the power of the 5160 and costs $4 shipped from China...)