ard at p850ug1.demon.co.uk
Sat Jan 27 15:46:02 CST 2007
> 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).
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