[sebhc] H89 Power-up problems.

Roger Birkholz rogbirk at gra.midco.net
Sat Jul 8 22:45:15 CDT 2006

Try scoping the power supply. I had a 5 volt regulator (not Heath) with a
open electrolytic. It measured 5 volts with a VOM but the scope showed about
a 10 volt square wave. Just a thought.

----- Original Message ----- 
From: "Lee Hart" <leeahart at earthlink.net>
To: <sebhc at sebhc.org>
Sent: Friday, July 07, 2006 9:55 PM
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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