Shift key not working on Apple II+

[tezza]

Hi,

I was playing around with my Apple II+ today and noticed a strange symptom on bootup. The shift keys would not work. For example, <shift>1 was still one, <shift>2 was still two etc. rather than the uppermost symbol on the key.

No matter which shift key is depressed, they dont' seem to work.

Thing is this seems to be an intermittant fault. It fault is more common than not but sometimes it disappears and behaviour reverts to normal. The next time I switch the machine on though, the fault is there.

Does anyone know what might be causing this, or can give me some pointers to which part of the circuitry to explore? I had no cards plugged in.

Tez

 

[scommstech]

Apple II keyboard

Apple II keyboard

Hi,

I was playing around with my Apple II+ today and noticed a strange symptom on bootup. The shift keys would not work. For example, <shift>1 was still one, <shift>2 was still two etc. rather than the uppermost symbol on the key.

No matter which shift key is depressed, they dont' seem to work.

Thing is this seems to be an intermittant fault. It fault is more common than not but sometimes it disappears and behaviour reverts to normal. The next time I switch the machine on though, the fault is there.

Does anyone know what might be causing this, or can give me some pointers to which part of the circuitry to explore? I had no cards plugged in.

Tez

As it effects both shift keys its unlikely to be the keys themselves.
My circuit shows both keys wired in parallel with one common
wire to the decode chip on the keyboard itself.
could be the chip just needs reseating.

 

[tezza]

Yes, I'm sure it's not the keys themselves. They both show the symptom and when it comes right, they both come right.

Thanks, I'll see what ICs are socketed on the keyboard and give that a go.

Tez

 

[cosam]

Might also be worth sticking an ohm meter on both ends of the common trace/wire. Any cable connectors on the way are also good candidates for reseating.

 

[tezza]

I checked this out today. Removed the keyboard circuitboard, reseated chips and cleaned interface pins.

Problem gone.

Tez