Apple ][e non registering some keys

[orlandoave]

Working on one of the early Apple ][e's with the white letters. What is stumping me is several keys are not functioning.
I have replaced all the chips in the extended ][e set with the originals, which includes the keyboard ROM, replaced all mb ram with new
chips, cleaned all keyboard connectors and re-flowed the keyboard backside motherboard connectors.
Of course replaced the keyboard with a known good one. Still have the same keys not functioning.
I noticed that without any key board plugged in there is no boot just the bummm sound. Did not know if
this is the way the older ][e's were.
The computer passes built in diags with the kernal being good. Of course I checked all traces.
Any ideas?

 

[thenzero]

On mine the L and ; keys stopped working at one point. I removed the caps and blew air into the switches and then exercised them up and down quickly. I’m guessing this isn’t your issue but that’s what got mine working again so thought I’d share.

 

[VERAULT]

The keyswitches have corrosion. You need to desolder the switches . open them up .. Insert some deoxit and press them a few dozen times. Check for proper continuity before reinstalling.

 

[ScutBoy]

Bang on them a lot - like dozens of times. Eventually they will start registering. You will have sore fingers A little deoxit down the stems can help. Luckily I've never had to the switches apart.

 

[VERAULT]

yeah that will work to a point, but desoldering cleaning reinstalling takes 5 to 10 minutes... its quick and easy once you get good at it.

 

[thenzero]

Just want to draw attention (for those with more experience than me on this subject) that you said you completely replaced the keyboard and still have the same keys misbehaving, which strongly points away from anything to do with the key switches as the culprit.

 

[thenzero]

(Is there a particular pattern that you’ve noticed with the missing keys? One side of the board or the other for example?)

 

[VERAULT]

Good eye then zero. The only two culprits are the keyboard ribbon cable or the keyboard encoder chip. I would lean towards the encoder.