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



retrogear
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:
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Pressing C generated a color bar pattern which also revealed the problem:
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Executing the video memory test revealed a bad memory chip U353:
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Subsequent testing showed U347 and U340 also bad. Here is the video board removed and flipped up to reveal the video ram:
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After ordering and replacing 3 ram chips the stray pixels were gone and the ROM color test pattern looked clean:
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After replacing U340 the problem disappeared, so may have been the only bad ram chip? Who knows ... Fun stuff !!

Larry G

ronwoch
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