Apple IIgs keyboard corruption: Repair ideas?

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Eudimorphodon's picture
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Apple IIgs keyboard corruption: Repair ideas?

Problem:

I was given a completely peripheral-less ROM 01 Apple IIgs "Woz Edition" the other day. Hoping to have some fun with it I spent a few bucks on an ADB keyboard, mouse, and serial cable (all the parts I could get from Weirdstuff), and was in the process of trying to hunt down a floppy drive when it occurred to me it would probably be a good idea to test the machine. And it has a problem.

At first glance the system appears to work, IE, when you power it up you get the appropriate noises and it displays the messages about "check boot device" after a few seconds of failing to find a floppy, and by using the proper key combination you can drop it into the control panel and navigate around. However, after using CTRL-(powerbutton/reset) to drop to Applesoft a severe keyboard corruption issue becomes evident. Basically it seems like on a semi-random basis some other keypress gets substituted for the correct one. For instance, if you hit the number "1" as the first character at the beginning of a line you'll get a "9" instead. (Higher numbers will get substituted for some punctuation mark or whatever.) But, and here's the fun part, a subsequent press *will* produce a 1. And will keep on producing 1's until you hit some other key, which may or may not register correctly on the first try.

Obviously my first thought was that the ADB keyboard was bad. However, by sheer happenstance I had an Apple IIe keyboard (just the keyboard and cable, nothing else) in my junk box so I've tried connecting that to the keyboard connector on the system board and testing that. And using the Apple IIe keyboard the pattern of scrambled/mismatched letters is the same.

Does this sound familiar to anyone, and is it likely to be repairable with parts that aren't unobtanium? (IE, need to be harvested off another IIgs motherboard?) My soldering skills and electronics skills aren't *great* but I have successfully repaired things like a DOA Commodore PET before so I'm willing to get my hands dirty.

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Re: Apple IIgs keyboard corruption: Repair ideas?

I had once a quite similar case with a bad Mega2 chip.....
in that machine it was also not possible to use any of the slots.... and only internal devices able to access....
if you have a DISK II controller at hand and just try to boot from DISK II after the option was set to
"your card" in the according slot.....
and no boot possible
and after changing to another slot with same procedure and still not booting....
then it might be useless wasting further time.....
sincerely speedyG

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Re: Apple IIgs keyboard corruption: Repair ideas?

I get the impression from your post that the IIgs uses a dumb keyboard. This makes things more difficult. Cleaning the key contacts will probably not help.

Try heating the motherboard with a hair dryer to see if heat changes anything. Try cooling the motherboard with freeze spray to see if cold changes anything. If the answer to either of these is yes then you probably have a bad solder joint on the motherboard.

I had a similar problem on my IIe. It turns out that there was some rosin on the motherboard that corroded a solder joint.

If you are in the mood, pull all the chips that are in sockets and clean the pins with a pink eraser. Keep yourself grounded when you do this.

Be Happy

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Re: Apple IIgs keyboard corruption: Repair ideas?

When you clean the chips, clean on the inside of the pins. That's where contact is made with most sockets.

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Re: Apple IIgs keyboard corruption: Repair ideas?

Sockets use different contact methods. You have already removed the chip from the carrier so clean both sides of the pins.

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Re: Apple IIgs keyboard corruption: Repair ideas?

Alas, being an Apple IIgs there aren't very many socketed chips in it. I've determined after some digging the keyboard functions are handled by a pair of proprietary surface-mount ASICS, the "keyboard controller" and a "Glue" chip, so any optimism I had for repairing this myself is fading rapidly. I was *really* hoping it could be something "analog" like bad capacitors or something, but the fact that it does exactly the same thing (every time) with both the ADB keyboard and a simple matrix sort of torpedoes that hope in my mind. I assume the keyboard controller communicates directly with an input port on the "MegaII" chip?

I guess I'm probably down to perhaps probing the power supply leads for the various silicon blobs and hoping that I see some obvious problem there that could be causing the keyboard controller to repeatedly reset or something. Sigh. The only other thought I can think of is if there were bad RAM in a keyboard input buffer area or something, but I'd need to read deeper about how an Apple II actually handles that to guess if that's worth chasing.

(One thing I'll say about working with a machine like a PET, there's lots of easy-to-find glue you can clamp the oscilloscope to. Darn the march of progress.)

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Re: Apple IIgs keyboard corruption: Repair ideas?

well as i said.... both keyboardconnectors go to the keyboardchip in the front right corner... and from there the ADB goes to the MEGA2 chip....
the only external capacitor to check is C71 just between keyboardchip and frontside of the computer.... but that is only responsible for "debouncing" the keys on the keyboard.... maybe a change might help... but if the other test i proposed fails... i.e. no slot useable with a IFcard... then its the MEGA2 .... and if it´s that one - your done if you don´t have experience with bonding....
anyhow a check of C71 won´t take much time...
speedyG

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Re: Apple IIgs keyboard corruption: Repair ideas?

I don't have *any* Apple II devices to test with (IE, a Disk II controller), but I was told by the person I got it from (who'd gotten a pile of them) that they'd successfully booted a disk with a drive connected to the built-in controller. They just admitted that they hadn't tested any deeper than that. So apparently at least *some* of the machine works... but anyway. Sigh.

I *might* be able to get my hands on either another complete machine or a motherboard. If that happens maybe I can use this one for parts. If nothing else I could steal the 65816 CPU and build an upgrade for the PET out of it.

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Re: Apple IIgs keyboard corruption: Repair ideas?

Hello Eudimorphodon,
that does not stand against my explenation.... as i explained if the MEGA2 chip is only partialy out of order the internal ports are still working... so it is probably still possible to boot from the smartport using the woz-machine chip... the damaged computer i examined did that too.... as i explained the mistake is indicated by the use of the slots - not the internal devices....
but if the computer is dead as i guess ... then it is a good idea to save at least everything that can be saved from that board as spareparts....
speedyG

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