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apple II plus keyboard repair suggestions

A

acenewman

Experienced Member
Joined
Apr 6, 2020
Messages
117
Location
Farmington MI
Purchased an Apple II plus recently. Has a number of keys that don't work very well. Has the cheaper keyboard, the one you can't replace the key switches on. Wondering if anyone has repaired this type of keyboard? Is it even worth attempting? Seen a few videos of folks messing with them. Seems like a giant pain in the butt. Any recommendations? Would hate to put a bunch of time into it just to find out there was not much chance of success. Thanks, Chris
 
The thing to determine is if it is just the switches, or possibly the encoder board. The way to determine one or the other is to get a hold of any one of the Apple II repair guides, and particularly study the keyboard switch layout. Use the following image as a guide:

https://68kmla.org/forums/uploads/monthly_08_2014/post-2328-0-94114700-1408543625.jpg

If the keys that don't work belong to a particular row or column (X or Y used on the image,) then it could be the encoder board. If the non-functional keys are randomly scattered all over the place, it could still be the encoder board, but more likely the problem are the switches themselves.
 
good idea, will do some more testing tonight to verify which keys don't work and if they all fall on the same row or column. The gentleman I bought it from said he found only one key to not work, I found more like half a dozen in my initial testing. Not that it really matters, he sold me the whole system (computer, 2 drives, monitor and monitor stand) for $50. I would have taken it if none of the keys worked ;) After some clean up and testing it seems that the only real issue is the keyboard. Thanks, Chris
 
After some more investigation these are the keys that are not working (3, Q, T, S, D, Z). All except T are on the Y0 line. Can't get a single letter out of these keys. There were a few others that were intermittent (Y, V, 8) but they seem to have come back with a little bit of exercise. I found the SAMS guide online. It's trouble shooting procedure suggests replacing the 74LS138 at F13 and then the 2513 (Character ROM?) at A5 as the first two checks. I will dig out my other II plus tomorrow and swap chips and see what happens.
 
Keep in mind that the Apple II Plus keyboard has its own processor. The only thing that comes out of the keyboard (besides the hard RESET) is the ASCII code value of the key pressed, hence the keyboard is a parallel ASCII keyboard. Which basically means whatever fails on the motherboard in relation to the keyboard would affect all keys and not just certain keys. If only certain keys are failing but all other keys are outputting their correct ASCII values, I don't think there's anything on the motherboard that is bad.

The only thing I can think of that could be bad on the motherboard would be, for example, if one of the bits in the ASCII output is being lost by a chip on the motherboard. But even if that was the case, you'd get garbage from these keys instead of nothing.
 
interesting development this morning. Powered the computer on and all of the keys except the T seem to work fine. T is the only one that isn't on the Y0 line, it's on Y4.
 
Well I took the plunge and tore apart the RFI keyboard last night. Found a fair amount of some kind of debris floating around inside. Cleaned things up with a damp towel. After using some tape to hold the plastic piece to the PCB and some careful reassembly the keyboard is working fantastically. In fact the repair went so well I decided to tear into another RFI keyboard (with key issues) I have been storing for years and it is working flawlessly now as well. In the end I would say the tape was the key ingredient. No way your gonna keep the plastic sheet aligned with the PCB without the tape, IMHO. Chris
 
The metal bits do go adrift. They are meant to sit on plastic pegs as I recall.

I 'reformed' the pegs with a soldering iron (yes, an old one just for melting plastic :) ) then topped them off to fix the strips in place.
 
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