View Full Version : bad video ram in Zenith Z-100

November 16th, 2015, 07:34 PM
I was noticing pixelated video in my newly acquired Zenith Z-100. It has a version 2.5 ROM with built in diagnostics. I set it to manual boot and got to the diagnostics test menu by pressing T. Here is the pixelated menu:
Pressing C generated a color bar pattern which also revealed the problem:
Executing the video memory test revealed a bad memory chip U353:
Subsequent testing showed U347 and U340 also bad. Here is the video board removed and flipped up to reveal the video ram:
After ordering and replacing 3 ram chips the stray pixels were gone and the ROM color test pattern looked clean:
After replacing U340 the problem disappeared, so may have been the only bad ram chip? Who knows ... Fun stuff !!

Larry G

December 2nd, 2015, 10:03 AM
Nice! I love playing with these machines. Just finished moving, so I am looking forward to getting my basement laboratory set back up! :D