[sebhc] H89 Power-up problems.

Mark Garlanger garlanger at gmail.com
Sun Jul 9 01:14:17 CDT 2006

On 7/9/06, Lee Hart <leeahart at earthlink.net> wrote:
> Mark Garlanger wrote:
> > As for the multiple H: prompts, when it happens, it is ghost images
> > (shaky screen, misplaced and lighter than normal). One H: prompt
> > that the video somehow decides to show in 3 locations at once.
> Ah, I see. The CPU board probably sent a single "H:", but the TLB is
> displaying it in several places.
> If the screen has a stable 80x25 character matrix and the H: appears in
> multiple places, it could be the video RAM malfunctioning.
> If the screen is rolling vertically or squirming diagonall or side to
> side, then the video board isn't syncing to the TLB (wrong or missing
> Hsync or Vsync).

Not really rolling, but definitely not in the correct 80x25 matrix,
top one is nearly off the screen and to the left.

> A bad keyboard encoder that is static damaged will send phantom keys
> (keys you didn't hit), or fail to send keys you do hit, or auto-repeat
> keys at random. For some reason, the keyboard encoder Heath used is
> unusually easy to damage from static.
> This chip can also malfunction if the 12v supply to the keyboard encoder
> is bad.

I was able to locate the right schematic and check the power going
into the TLB board (strange that it comes from the CPU board and not
the power supply).  From your earlier posting:

> 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.

The values on my DMM are +7.3V +17.6V and -18.1V...
Most likely the +7.3V is the source of my problems. Based on the
schematics, it appears that the keyboard encoder uses Vcc2 (one of the
5V supplies).

I measured the one you sent me and see just over 9V on that same line.

But then I checked the wall voltage: 117V!!! what it should be 120V?
Well there is alot of computer equipment in this room... Tested my idea by
I turning on the laser printer... down to 115V with dips down to 112V.
Turned off all no essential lights/monitors/systems... and it's up to 118V.

I guess this H89 is more sensitive to low voltage, but low voltage seems to
be the problem. I'll need to either move some of this equipment out of
this room or figure out a way to get a dedicated circuit or two directly from
the service panel.

With the laser printer on I was able to see problem with the terminal portion.
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