Heathkit-Zenith H/Z-19

[Tony Duell]

> 
> I have an old Heathkit-Zenith H/Z-19 terminal, and I am trying to
> use it to connect to a Linux system. I have it set up successfully to
> connect to the Linux machine, but I have a small problem. The bottom
> half of the H/Z-19 screen is filled with "p"s in reverse video. When I
> reach that part of the screen, everything I receive is gibberish. Most
> of the characters show up as some other character. Once I reach the
> very bottom of the screen, the "p"s scroll up with the rest of the
> text, but come back again from the bottom. I believe this is a memory
> problem, but I do not know if I am correct. Do you know what could be
> causing this? If so, how could I fix it?

Sounds like a video RAM failure. specifically the low nybble of the 
second half of the RAM..

What follows is how _I_ would starttrying to fix it. Others may just want 
to swap the terminal logic PCB (assuming you can find one).

I have the scheamtics of the terminal logic PCB in front of me. The video 
RAMs are U408...U411 and look to be 2114s. That type of RAM chip is 
well-known for failing.

The low nymblrs are U408 and U410, at a quick glance you wany to change 
U410. Those are a column of 4 18 pin ICs to the left of the crutal (U401), 
in order U408, U410, U411, U409, with the edge of the board with the 2 
voltage regulators at the top (I am assuming you don't have the 
'illustration booklet' that shows the PCB).

-tony