help with keyboard problem

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Last seen: 5 months 3 days ago
Joined: Apr 10 2021 - 12:07
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help with keyboard problem

So I have a II+ and the keyboard was mostly working but there were a few keys that would either not work, repeat, or just occasional work.

 

I dripped a few drops of deoxit down the plungers and all the keys that were not working started working. Next I recapped the power supply and the computer boots but none of the keys are working but the power light is working on the keyboard.

 

Where should I start troubleshooting ? Keboard encorder or system board? 

 

What should I be looking for?

 

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Last seen: 5 months 3 days ago
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also the ctrl+ reset works

also the ctrl+ reset works and if i change the switch on the encorder board the reset key by itself works

 

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Joined: Feb 27 2021 - 18:59
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Regressions and units

When doing repairs, a "regression" is when something that worked before stopped working. Regressions are the reason that you always should test everything after each change that you make. That narrows down the possible causes to just the last change.

If the only change that was made between the keyboard working, and not working, is the power supply, then the cause is the power supply. "Elementary, my dear Watson." That doesn't mean that the fix must be in the power supply only: if the cause of the problem was a damaging fault, it could have damaged components in other places that now will need to be replaced.

The other rule for testing is that after fixing a subassembly, to the fullest extent possible you should test that assembly in isolation. After working on a power supply, it's best to test that it behaves properly when run unloaded or connected to a "dummy load" that is just a resistor. (If the power dissipated by the resistor needs to be high, it may need additional cooling.) This protects the computer from damage in case the power supply became faulty as a result of the work done on it.

In programming these so-called "unit tests" and "regression tests" can be automated so they all happen without any added work: a good practice that saves time and catches errors. In repair there is no shortcut, so you need to know how much time to spend checking your work for errors. The answer will depend on your skill level and the value of the equipment, but a good guideline is to check everything that you did at least twice. This helps to catch "confirmation bias" where you are too certain that your work is good if you see the expected measurement the first time.

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I don't think the power

I don't think the power supply is the issue as all other components are functiong and the voltages from the power supply are correct according to my meter.

I only have the one computer so trying a different encoder board or complete keyboard aren't an option. I have ordered a Apple II to PS/2 keyboard adapter to test if the mother board works without the original  encoder+keyboard I have. 

Just wnated to know if anyone had this issue before and if so how they fixed it.  All suggestions are welcome.

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Last seen: 18 hours 9 min ago
Joined: Apr 26 2016 - 08:36
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It's awfully suspicious that

It's awfully suspicious that one day the keyboard worked, and the next day the keyboard didn't.

That behaviour you described suggest that the keyboard is getting power thorugh the ribbon cable, and the sub-circuit that governs the CTRL-RESET behaviour is working fine.  Since the RESET key bypasses the encoder and is connected directly to the RESET circuit on the motherboard it's not an indicator of anything special except maybe that your keyboard encoder is somehow faulty or you mis-plugged the riboon cable into the motherboard - checking that for a bent or broken pin is the first thing I'd try.

 

 

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I checked the ribbon cable

I checked the ribbon cable and the pins and everything looks good so I guess I'll wait for the ps/2 adapter and see if that works which will point to the encoder board. Trying to not have to by an entire keybord since whats on ebay costs almost as much as I paid for the computer

Thanks for the info

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