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Apple IIe Keyboard Help Please...


SonicExplorer

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Original owner of an Apple IIe which I dragged out of the closet last week and everything so far seems to work - except for the keyboard.  I either get no response to any key, or the system auto-repeats on it's own.  I've tried re-seating both ends of the ribbon cable, no change.  IIRC this problem started surfacing intermittmently back when the computer was only about 5 years old .... I never did figure out what was going on.  Anyway, very clean machine inside and out.

 

Anyone have ideas or troubleshooting tips for this particular scenario...??? 

 

Thanks,

 

   Sonic

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Ok, so after a lot of online research it seems I should try <ctrl> + <reset> since that apparently bypasses the KB encoder chip.  If that works, then it is a hint the encoder might be the issue.  Also, I could try to do some continuity with the KB and cable (if I can find something small enough to get into the cable pinholes.   Unfortunately the KB cable format is not common nor readily available to try swapping out.
 

To be more clear, the KB is the 'white symbols on the keys' version.  And when the computer is powered up the screen either displays the usual prompt yet nothing on the keyboard works.  Or else the screen continually repeats a blank character (what I suspect is a space character but can't be sure).  I tried disconnecting the KB cable and powering up but the system didn't like that at all - random garbage on the screen. So the system does seem to recognize when the KB cable is unplugged if that provides any clue?

 

Sonic

Edited by SonicExplorer
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24 minutes ago, SonicExplorer said:

I tried disconnecting the KB cable and powering up but the system didn't like that at all - random garbage on the screen. So the system does seem to recognize when the KB cable is unplugged if that provides any clue?

 

That would be the diagnostics running. A standard and expected activity with keyboard unplugged.

 

When I'm confronted with wonkey keyboards I first clean all the switches, continuity test the cable and connectors, and resolder suspect key-switches (or all of them for good measure). Then test each one with DMM. Then after that I start looking at the mainboard.

 

You can test/swap with a spare keyboard if you have one.

Edited by Keatah
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Thanks, no spare parts unfortunately.  The machine has been kept indoors, covered with cotton cloth and under air conditioning since the beginning so I'm doubtful it's dirty contacts.  Even the KB pins were sparkling gold. I did spray some contact cleaner into the KB cable pinholes, just in case.  Cleaned the KB PCB as well (just to eliminate the chance something was conducting across traces).  This KB weirdness started back long ago, which makes me suspect it may have been a faulty component of some sort from production.

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6 hours ago, Keatah said:

There've been times I used the wife's vibrator to buzz keys back into working. Corrosion builds up on any switch that isn't used. And keyboard switches are gentle things with minimal pressure to rub away any build-up.

First time I have heard something like this. At the job we have vibration tables to test the manufactured equipments, but in case of the keyboard maybe Contact Cleaner will help.

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Update:

 

So, the various ctrl-reset (and open/closed apple variations) all work. And with my limited understanding of how to read a keyboard schematic and continuity check I was at least able to verify the space bar and a few other keys are 'working' from a continuity check perspective.  I also tested continuity from each PCB KB connector point to the other end of the cable and all 26 lines had continuity.

 

I tried to pull the large (is it KB encoder?) chip, but it isn't budging, afraid I will snap it.


What now, any other ideas ??

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You'd have to use some sort of thin wedge. Something to slide under the chip, between it and the socket. And gently work it up. A little at a time on each side. I've also used a bit of DeOxit on stuck chips. A tiny drop on each pin. Then press it down and start pulling & prying.

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Based on my situation, do we know which chip is the one to try reseating?  Is it the KB decoder or KB ROM or timer chip ??  If this isn't a chip-contact issue that reseating will fix, my next guess is either a bad chip or one of the filter capacitors (such as on the timer pins) is bad.  But I'm purely speculating...

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Update:


Well, I managed to remove the KB decoder and ROM chip.  Pins looked shiny new and reseating didn't make any difference.  So I'm about to give up on this for now, may put the machine up for sale, which is a shame given the rather excellent condition it is in.  But I don't have time to chase spare parts for swapping nor to drag out the O-Scope hoping to recall college electrical engineering courses.  lol


If anyone happens to think of any other troubleshooting ideas please let me know...

 

Sonic

Edited by SonicExplorer
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  • 2 weeks later...
On 7/19/2022 at 4:42 AM, SonicExplorer said:

But I don't have time to chase spare parts for swapping nor to drag out the O-Scope hoping to recall college electrical engineering courses.  lol

I get it.

 

Playing with scopes and meters is par for the course when owning and working with vintage computers. When pushing and cleaning stuff doesn't work it means something is bad and you gotta find it with random parts swaps or your test equipment.

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Pretty sure I recall a C70 and C71 being related to something like this issue. One of those is for the bounce mask and the other is for the keyboard controller's clock. They should be right under the keyboard encoder chip. Cheap and easy to try. Might even be able to scavenge those from other junk boards.

 

Also you should use the OHMS scale when checking the keyboard switches (if you didn't) and not the continuity beep. We're looking for stray resistance. The continuity function doesn't really fire on large value resistances. But the keyboard encoder would.

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