VT101 screen adjustment
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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