[Coco] CoCo 3 Display Problems

Kurt Randall kurtrandall at gmail.com
Fri Sep 25 15:21:24 EDT 2020

Just wondering if anyone can help me with a problem I have with a CoCo 3 I
recently picked up. I'm new to CoCo's -- my 8-bit computer experience is
with ti99's, Apple IIs, and ZX Spectrums.

My problem is that the display in both RF and Composite is shaky, but the
problem goes if I plug in my CoCo SDC. I have one game cartridge, and that
seems to help too.

I tried re-seating all the socketed chips, cleaning connections, tried a
couple different cables, and a couple different screens (LCD tv, CRT
composite monitors, CRT tv). Without the SDC plugged in, the LCD tv always
has problems with the top of the screen -- the top moves back and forth
about 1/4 of the way across the screen, while the bottom is fine. The CRTs
have shaky horizontal stripes -- it looks like every second line is a bit
wiggly, but they are usable.

If I plug in the SDC the CRTs are fine, while the LCD is only fine unless I
try running a game, then the problem comes back.

Anything I should be looking at? Capacitors perhaps?


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