Weird Apple IIe (non-platinum) keyboard issue

[dyelton]

I've had an Apple IIe (non-platinum 1984 edition with beige keyboard) that's worked great since I obtained it several months ago. I don't turn it on very often but I just bought an excellent condition keyboard to replace the one that was in it since it had a couple of broken key studs.

After replacing the keyboard and turning it on, the keys seem to stick...actually ALL of the keys stick. Hooking up the OLD broken keyboard that I know works gives the same result (keys sticking). Running a self-test (Ctrl+Open Apple+Closed Apple+Reset) gives a system ok. I've also reseated the keyboard controller IC but nothing has made a difference. I've even taken out all of the expansion cards (e.g. 64k ram card, disk controller card) out but nothing made a difference.

Any ideas as to what could be causing this out of the blue? Apple II forums are hard to find so I'm hoping there are still folks around on this site who are still up for vintage troubleshooting.

 

[madmax_2069]

Have you tried posting about this on atariage in the classic computing section? There are a few apple people there that could help you out.

 

[dyelton]

Have you tried posting about this on atariage in the classic computing section? There are a few apple people there that could help you out.

Thanks for that! I didn't know about that site. I'll definitely make a post on the issue but I think I may have come to a conclusion. In my research I found a link to an old repair guide for the Apple II/IIe that mentions my very problem. Looks like it may be the decoder part of the encoder/decoder IC. A bit hard to come by but you can usually pick up a poor/fair condition Apple IIe from eBay fairly cheap these days that I can just extract the chip from.

Thanks again!

 

[tdiaz]

Remove the floppy controller and any hard disk controller. (You want nothing that boots)

Turn on the computer so it goes straight to the ]Prompt.

IF any key is stuck, you'll see it repeating right then.

IF you press any key that stays stuck afterwards, it will .. of course, repeat.

If you have a stuck key, and you press something else, that something else will take over from the stuck key and itself will now repeat. That could be why you are describing that they all repeat.

At the prompt, hold down A, for example. While holding A down, press B, and let go. The repeating will pause for the 1 second that is the normal delay before repeating, and then you will see B repeating.

Press C, and let go.. same thing.. C.....

Etc.

Thats why yanking the drive controllers will let you see the stuck key, if any, on power up.

 

[MacTech68]

Remove the floppy controller and any hard disk controller. (You want nothing that boots)

Turn on the computer so it goes straight to the ]Prompt.

IF any key is stuck, you'll see it repeating right then.

IF you press any key that stays stuck afterwards, it will .. of course, repeat.

If you have a stuck key, and you press something else, that something else will take over from the stuck key and itself will now repeat. That could be why you are describing that they all repeat.

At the prompt, hold down A, for example. While holding A down, press B, and let go. The repeating will pause for the 1 second that is the normal delay before repeating, and then you will see B repeating.

Press C, and let go.. same thing.. C.....

Etc.

Thats why yanking the drive controllers will let you see the stuck key, if any, on power up.

And so, by this method, the first key that repeats is the one with the problem.

Nice, I was racking my brains trying to figure this one, but the above is sound advice.

If you have a logic probe this PDF may help:

http://www.bitsavers.org/pdf/gi/_dataSheets/AY-5-3600.pdf

Especially the "Strobe Delay" input to pin 31. Check the connected capacitor or replace. Rarely do Disc ceramic or Mono ceramic caps fail but they most certainly CAN fail.

 

[dyelton]

Thanks for all of the advice guys! Unfortunately I don't have a way to test the IC but I do have a couple of IIe boards on the way to keep in my closet. I'm going to replace the 47pF capacitor with a new one to see if that resolves it while I'm waiting for the two extra logic boards to arrive so that I can switch out the decoder if necessary.

I'm curious though...finding a 47pF 50v 5% ceramic cap is a bit challenging. I realize Digi-Key has them, but paying shipping for even a few caps is ridiculous. Would a 47pF 50v 10% work as a replacement? I'm not sure how much the 5% variance makes for this application.

 

[tdiaz]

10% is fine. If worried, get a few of them. You gotta figure it this way:

The value is supposed to be what it stated, but it could be up to 10% off.

Well, the one that's on there could be up to 5% off. That means the thing could work fine within a 10% spread from extreme to extreme.

If you have a few of those 10%'ers, and you land in the same window of performance of the 5% part, then you are working the same, right?

Basically, if you put it on there and it's really wonky, use another one. It's not going to get any worse.