[sebhc] H89 Power-up problems.

Mark Garlanger garlanger at gmail.com
Fri Jul 7 16:57:10 CDT 2006

Hi Guys,

  Thanks for all the suggestions. When I last turned off that H89
(about 3-4 days ago), it was still having the problem. 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). On my other
H89, I am unable to get any of the keys to act this way.

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

BTW: It still usually only beeps once even though the computer part is
working.  It could be the timings that Lee mentioned below, since once
(out of about 10), it did beep twice.


On 7/5/06, Lee Hart <leeahart at earthlink.net> wrote:
> Mark Garlanger wrote:
> > Does anyone know what the power up beeps mean?
> The TLB and CPU boards each independently generate a "beep" when they
> are powered up. The speaker plugs into the TLB, so you get one "beep"
> for an H19 trminal, or for an H89 with the OFF-LINE key depressed.
> This first "beep" tells you that the TLB has power, and that its Z80 is
> running and executing software (even if incorrectly). It will "beep"
> again each time the TLB is reset.
> The CPU board in an H88/89/90 generates a separate "beep" when it is
> powered up or reset. To hear this as a second "beep", the TLB needs to
> be working, and on-line (i.e. the OFF-LINE key is up). This "beep" is
> sent to the TLB serially as a software command at the same time as the
> "H:" prompt. It indicates that the CPU board's Z80 is running the
> monitor program.
> Note that the timing of these "beeps" is set independently by the R-C
> networks on each board that control the power-on Reset. Old TLB and CPU
> boards tended to have long delays; later ones had shorter delays. It's
> possible to swap boards so you have a long delay on the TLB and a short
> delay on the CPU -- when this happens, the CPU board sends its "beep"
> before the TLB has started running, so you only get one "beep" even
> though nothing is wrong.
> > working fine, but now the keyboard no longer works (except for the
> > 'shift-reset' combo), all other keys don't even keyclick (they had
> > initially).
> The keyboard encoder chip is an old PMOS part, and pretty sensitive to
> static damage. Touching the bare keyboard connector pins or traces to
> the keyboard can kill it. If the problem isn't something simple like the
> ribbon cable to the keyboard being unplugged, you may have a bad
> keyboard encoder IC.
> > Between the time it was working and now, during a few power-ups the
> > screen the screen went a little crazy, for example, the "H:" was
> > shaking and showing up in two places, another time various characters
> > showed up on the screen. I'm wondering if a CAP or other component
> > failed.
> These symptoms both point to problems on the TLB. I'd check the supply
> voltages. The TLB needs +8v, +16v, and -16v to work. It has onboard
> regulators to convert these to +5v, -5v, +12v, and -12v.
> > BTW: The memory is installed strangely in the system. The top row of
> > memory ICs have a second memory chip soldiered on top of each one,
> > along with a wire that connects them all to one of the lines on the
> > slot that you would normally install the extra memory card to bump it
> > up to 64k. This must have been a cheaper way to get to 64k than adding
> > the board.
> Right. This is a 'quick and dirty' way to upgrade to 64k of RAM without
> any extra PC boards.
> --
> Ring the bells that you 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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