VT101 screen adjustment

Swift Griggs swiftgriggs at gmail.com
Mon May 9 16:15:46 CDT 2016

On Mon, 9 May 2016, Adrian Graham wrote:
> Thanks for that, I now know it's vertical deflection which is adjusted 
> by A102 on the monitor board so I'm just about to give it a tweak once I 
> find my plastic trimmers and a screwdriver small enough to get the top 
> off, it's the only VT1xx I have with all fasteners intact.

No problem, I've often noticed a couple of things you should know:

1. Many times the pots are plastic. Be careful when you first "break" them 
loose, I've ruined a few in Trinitrons which were stuck so hard the thing 
kind of fell apart when twisting it. 

2. Make darn sure you discharge the tube before you work on it. I use a 
flathead screwdriver with a 12g wire attached to it that runs down to 
grounded pipe. They will zap the living snot out of you if you don't. Just 
tie off the wire to a grounded source then stick the screwdriver 
underneath what looks like a little suction pad on the tube. You'll 
usually hear it discharge with a POP! If you already knew this, sorry, but 
I wanted to be sure you didn't get shocked. Messing with the CRT logic 
board is a great way to take a few thousand volts. :-)

3. Those CRT logic boards are usually replaceable all as a piece. Also, as 
someone already stated, they often have caps on them which impact the 
vertical sweep. If those go out, adjusting the pots does nothing or makes 
things look ruined/jittery. Some people can re-cap them, I've only done 
that once with another smarter guy watching me do it. I just usually 
replace the board if possible.

> Also that repairfaq lost me an hour at lunchtime while I read it, why 
> did I not know about it before!

Maybe you just hadn't needed to before. I used to work on monitors a long 
time ago, but I was never any good with electronics because I was never 
trained or self-motivated enough to learn digital theory or fight a logic 
analyzer or Verilog with any acumen. It's another hobby I'll have another 
go at one of these days. Today, I can mostly fix my guitar amps (old and 
analog), so that's good enough (for now). I learned those skills from 
doing electronics kit projects when I was a pre-teen and some extra analog 
tricks with a scope that I learned from an old hippie. I'll probably use 
the same sort of methods (but maybe start with some Arduino gear instead) 
the next time I try to pick up some more EE skills. It's hard not to be 
intimidated by all these guys on the list with mad electronics chops 
(Maciej, Eric, Fred and others are incredible; they know soooo much).


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