The repair shop told me they were replacing the safety cap, which they
didn't do (it took them three weeks to not do it). Oddly enough, the
safety cap is the only thing that's ever gone wrong with the TV until
now; it burned a 1/4" hole through the circuit board a few months after
we bought the TV. They didn't say that anything else was wrong, though
I wonder if they even turned it on.
The red trails behave exactly as you say when I turn down the
brightness, I guess that's a bad sign. It seems weird that low red
emission creates more red on the screen, but I don't pretend to
understand how the tube works.
I'll not worry about R400 and R401 except to fix the solder joints.
The set is in fact very old (I remember the phone conversation with the
TV repair people ... none of them had ever seen a TV in a wooden cabinet
before), but it's been rock solid until now so I hate to get rid of it,
especially because I wanted my next TV to hang on the wall, and I can't
afford that yet.
I'll fix the bad solder joints and replace those couple of resistors,
and see what happens. There is a small amount of documentation glued to
the inside of the set that has a bit of diagnostic information; I'll try
to read that a bit more closely and see what kind of voltages happen on
the CRT neck board. Replacing the tube seems a bit excessive given the
age of the set, so I guess I just nurse it along for a bit longer.
On a side note, I read on the Internet (so I know it's true?) that you
can do things like fiddle with the heater voltage to help the tube along
for a bit longer. Is this really safe? It doesn't strike me as a good
idea, but I like to explore all of the options (at least the good ones).
Thanks
--
Elliott
Bill Renfro wrote:
Hi Elliott
What did the repair shop tell you?
What you are describing sounds like the CRT is dying. The red gun has low
emission. That will cause the red bleed on the right side of objects. A
weak CRT will also cause the focus problem. Focus gets better after the CRT
warms up. When the set is on and warmed up, if you turn the brightness down
the red trails should go away, or be noticably reduced. The picture will be
dim, but will likely be sharp, and the color will be ok. When you turn the
brightness up the red trails will reappear.
The 12K resistors on Q11 collector connect to the 193volt source and are
likely overheating because of the low red gun emission of the CRT. The
other resistors are probably ok. If the picture colors are ok except for
the red trail the transistor is probably ok.
The only resistors in the signal path are the 330 and the 1.5K. The red
drive pot is also in the signal path, but these are likely ok.
The overscan could be slight blooming because of load on the high voltage
supply.
R400 and R401 are thermistors in the power supply. If the set is working
they are ok.
Remember the set is quite old, and CRTs don't last forever. I think you
may only be seeing the symptoms of the real problem.
To repair the set you would have to replace the CRT, and the 12K resistors
that were overheating.
Of course I haven't seen the set and neither of us has done any voltage
checks or looked at any waveforms or checked the CRT, so I may be totally
wrong. Just my thoughts based on your observations. That's why I wondered
what the repair man told you.
Good luck,
Bill
Christian Technology
"E P" wrote in message
om...
For a while there were big red shadows appearing on the right side of
objects on the screen; they were intermittent at first but now they
seem to always be there, and they're growing. I don't have the proper
tools to diagnose the TV, but I figure I can't do any worse than the
TV repair place I took it to did (they charged a big pile of money and
didn't actually do anything). There's another (presumably unrelated)
problem: when I turn on the TV, it's very fuzzy for about 30 seconds.
I figured I'd start with the color thing, and then tackle the focus
thing with a can of air and see if anything reacts badly to cold.
Then the third thing that bugs me is that the screen overscans about 1
inch too far all the way around. But one thing at a time...
While cleaning dust and grime off of stuff, I've noticed two bad
solder joints on the main chassis board, both on what appear to be
power resistors (R400 and R401). I'd replace them both if I knew for
sure what they are because R400 has a big crack along one of the flat
sides, and R401 has weird bubbles all over it. But they're both
connected to what appears to be high voltage, and I don't want to put
the wrong thing in there (maybe they're bleedoff resistors?).
Anyway, I'm looking at the output transistor for two reasons: first,
the two 12k resistors that are connected to the collector of what
appears to be red's output transistor (Q11) are both severely cooked;
second, if I unplug J18, the screen has this sort of red/brown color
(I assume it should be dark if there's no input signal).
[...]
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