[vcf-midatlantic] VT320 CRT replacement? - Rejuvination

[Jason Perkins]

At the end of the gun is a little can with emissive material. IIRC
it's barium. When you hit the tube with a rejuvenator it will heat the
filament up extra hot to get the material nice and warm, then give it
a zap to hopefully blow away any crust that's formed on the top of the
material.

The danger is that when you do this it can also boil off the remaining
material. If you get really aggressive you can blow away all the
material!

But like you said... if the tube is weak / junk anyway there's little
risk. Even if it's short lived at least you get some more good hours
out of it.

If you want to lean more about CRT rejuvenation, and other repairs I
suggest checking out bandersentv on youtube.

-J

On Mon, May 2, 2016 at 5:49 PM, Ethan via vcf-midatlantic
<vcf-midatlantic at lists.vintagecomputerfederation.org> wrote:
>>> 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 rejuvinators.
>
> This could probably stand to be figured out for NeXT displays as well.
>
> Also, put the CRT face down when you're rejuvinating it.
>



-- 
Jason Perkins
313 355 0085