[sebhc] H89 Power-up problems.

Lee Hart leeahart at earthlink.net
Wed Jul 5 20:33:40 CDT 2006

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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