[sebhc] H89 Power-up problems.

Mark Garlanger garlangr at verizon.net
Sat Jul 8 15:11:24 CDT 2006

It appears that the problem is the keyboard encoder chip. After a couple of
key presses today the screen went crazy... multiple 'H:'s on the screen,
then garbage, shift-reset not working then shift-reset working... Nothing
Any idea of a work-around since I'm guessing that the encoder chip is
no-longer available? Or should this just be my spare parts machine? I did
acquire a loose terminal board, but looking at the condition of it (not sure
of it's history), there is no chance that the chip is still functional. 


-----Original Message-----
From: sebhc-bounces at sebhc.org [mailto:sebhc-bounces at sebhc.org] On Behalf Of
Lee Hart
Sent: Friday, July 07, 2006 9:55 PM
To: sebhc at sebhc.org
Subject: Re: [sebhc] H89 Power-up problems.

Mark Garlanger wrote:
> Today, the keyboard is working (although not as good as on my other
> H89). Several of the keys seem to have problems with repeated
> characters (as if the debouncing circuitry is not working well).
> Several of the keys will intermittently generate 2 (or more)
> characters when I press it (more likely if I press it slowly).
> Also, the '4' key will intermittently not register on the key
> press, but will on the key release ( and sometimes on both).
> It doesn't seem like all the keys have the problem (not even all
> the keys in a given row).

These are the symptoms of a static-damaged keyboard encoder chip. There
might be other causes (bad voltage regulator that powers the keyboard
encoder, or loose or intermittent wiring somewhere), but my money is on
the keyboard encoder IC.

> Is there any trick to popping off the keys? Maybe they need cleaning
> underneath.

No, they just pull straight up to come off. There are multiple redundant
gold plated contacts per key, so it is pretty unlikely they are the
problem unless the keyboard has suffered some grevious abuse
(submersion, etc.)
Ring the bells that still can ring
Forget the perfect offering
There is a crack in everything
That's how the light gets in    --    Leonard Cohen
Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart_at_earthlink.net
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