[vcf-midatlantic] VT320 CRT replacement? - Rejuvination

Ethan telmnstr at 757.org
Mon May 2 17:49:36 EDT 2016

>> I have a VT320 with a pretty bad case of Being Old. The screen is so dim
>> that even with all the lights off in the basement, it's difficult to read
>> (and if it gets switched to 132-character mode, next to impossible). I know
>> surplus caches of these CRTs pop up every once in a while, and I know other
>> mono CRTs of the same size are often mechanically and electrically
>> compatible, but I'm a bit at sea. Does anyone have pointers for acquiring
>> such things?
>> The current tube is amber, but I really don't care what color it is as
>> long as it's legible.
>> Failing that, how well do rejuvenators really work on these? My
>> understanding is that it's usually a pretty temporary fix at best (like
>> Retr0Brite).
>> - Dave

Rejuvinators are maaagic! They burn the phosphor off the gun or something 
by hitting it with high voltage (110-120vac I'd guess.) But, it can go 
south and kill the crt. But if the CRT is weak, what's to lose? The 
rejuvinators can test and show you how good or bad the guns are, and then 
you can proceed to zap em and retest.

But that isn't the only potential for issue. Electrolytic caps that have 
gone weak in your terminal might be an issue. So replace all of those if 
this is full on project. Do that first.

It is possible to turn up the output from the flyback, there is usually a 
screen and focus potentiometer so you can turn up screen voltage (if you 
see the raster scan lines it's too much if such a thing exists on 
terminal) and you can focus it. BUT, if the tube is weak you will be 
driving the board harder, and could lead to early failure.

The big thing I think might be an issue is the rejuvinators have a set of 
CRT socket adaptors and a list of CRT models and numbers to use for 
rejuvination. I'm not sure that dumb terminals were the intended market 
for such a process, so you might need to look into things a bit harder and 
build a custom adapter. The arcade people are mostly into B&K/BK 

This could probably stand to be figured out for NeXT displays as well.

Also, put the CRT face down when you're rejuvinating it.

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