[sebhc] H89 Power-up problems.

[Lee Hart]

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).

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.

> This was an image I captured with my phone while I held the
> 'ctrl-reset' down during one of the messed up times(imaged stayed
> until I released the keys). Sorry for the bad quality, it basically
> had something like 'C', some graphic charaters, and a 'eM' repeated
> several times sloping down across the screen
> http://heath.garlanger.com/h89.jpg

The steady screen display, but oddball scattering of characters makes me
think the video RAM isn't working right (four 2114's).
-- 
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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