Free: broken but possibly fixable sync-on-green monitor

[Allison]

>
>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