5 Aug
1998
5 Aug
'98
9:39 p.m.
Tony,
It's _Very_ easy to modify the vertical scan rate. The horizontal scan
system is nasty to modify because (a) the flyback is tuned to (a harmonic
of) the scan rate, (b) the EHT voltage depends on the scan rate and (c)
the scan sawtooth is partially produced by the inductance of the yoke. So
changing anything there is a pain.
How far can you shift the horizontal frequency?
If you can fix TVs you're over halfway to fixing
monitors
And the horizontal output transistor 95% of the time. Flybacks and HOTs
are very expensive here if you order a specific part. The last flyback that
I got cost $80! If you can get a generic part number then they're a lot
cheaper.
it's not worth the time or parts that it
would cost to fix it. Or course,
Not so. Most TV faults can be fixed in under an hour using fairly cheap
parts. About the worst thing that's likely to go is the flyback transformer.
Maybe I only get the higher class of TV sets here,
They MUST be!
but I certainly find
them worth repairing. The cheap modern crap produces a
picture that IMHO
is unwatchable even when you've tweaked all the adjustments...
Then you should see the crap that they sell in the discount stores here!
Vertical
scan rates are a lot easier to modify, so those don't bother me
so much.
Have you done much of that? How successfull were you?
But the vertical system is more friendly. The sawtooth waveform is
produced in a low-level stage, amplified by what's essentially an audio
amplifier (in fact some TVs used an audio amplifier chip here), and sent
to the yoke. Given a data sheet on the chip you can normally figure out
what components to change.
Is it just a RC circuit?
Joe