Heath H19, was Computers for children - test-drb@ccmp.vtda.org

15 Jan 1999

At 06:54 PM 1/15/99 +0000, Tony wrote:
...
   3 other bits.
Much easier to "fix" than the MOS encoder chip, if that chip
 was programmed for a custom matrix, such as the Heath H19 terminal. 
I have the H19 schematics here (well, actually the Z90 schematics, but 
AFAIK the 'terminal' part of that computer is a H19), and I'm suprised 
that the encoder is custom. There's a ROM between the data outputs of the 
keyboard encoder and the data lines of the terminal processor. I would 
have thought that would have handled the translation for the custom matrix.

If they did use a custom version of the encoder chip, then what on earth 
is that ROM doing there?
 Yes, I found the manual and there is both an encoder AND a ROM. Seems sort
of redundant, can only guess why.  Many years ago the encoder chip died in
mine, and I first tried the generic version of the chip, most likely a GI
part. It didn't work, ended up ordering a replacement from Heathkit which
did work.

Also found that leaving the hinged case cracked open helped with the
cooling, the metal flange/heatsink on the pc board gets quite hot.

Never upgraded mine to a computer- Z89 or such. Thought at the time there
was a neat graphics add on for it as well.
-Dave