Free: broken but possibly fixable sync-on-green monitor - test-drb@ccmp.vtda.org

2 May 2005

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Subject: Re: Free: broken but possibly fixable sync-on-green monitor
   From: Jim Leonard <trixter at oldskool.org>
   Date: Mon, 02 May 2005 15:25:48 -0500
     To: General Discussion: On-Topic and Off-Topic Posts <cctalk at
classiccmp.org>

Tony Duell wrote:
  A word of warning to anyone who gets this... I
had an Apple Mac+ that had 
 a smeared display -- shaddows to the right of objects on the screen. Now, 
 the Mac+ video circuit is pretty simple, but none-the-less I spent quite 
 a time going through it, unable to find the fault.

 The reason I couldn't find a fault in the video amplifier was that there 
 wasn't one. It was the CRT. Low emission, I think. 

 Most of the time, a smeared picture _is_ a fault in the video amplifier, 
 though. But it may not be. 
I had a trintron tube connected to the same computer for 8 years slowly go 
"smeary" on me and I never found out why (monitor was on for only 3-4 hours 
each day, not 24/7).  The "smears" were always after a high-to-low or 
low-to-high contrast (ie biggest voltage change) on the screen and were always 
in the direction of the scan (ie left to right, eventually fading out at the 
far right).  Video card never failed once, and produced a perfect picture on a 
new monitor.

So what caused that?  What went "bad" over time to cause such a thing, and is 
it fixable? 
Actually the most common thing I've seen short of a complete horizonal 
output failure is the CRT focus pot and associated resistor string fails.
It's a gradual failure and for most color monitors that's part of the 
HV transformer assembly.  A few I'e stretched the life by adjusting 
the focus but sooner or later it fails and the images are just plain 
fuzzy. 

I think currently I have 4 in the garage that have either focus 
or horizonal output problems.  Anyone wants to pick them up and 
a few working tubes give me a email.

Allison