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).
My plan at this point is to replace all three output transistors, and
for good measure I'm thinking I'll also replace the resistors that are
directly in the signal path (for each color, that appears to be four
12k resistors, a 330ohm, a 3.3kohm, a 390ohm, a 150ohm, and a 1.5kohm;
I'm debating the pair of potentiometers).
Am I going about it right? I feel like I should do the same thing to
all three channels; even if balance isn't an issue, if one is dead
then maybe the others are on their way out. And although I'm sure
that most of the resistors aren't bad, resistors are cheap so I don't
see any problem with putting new ones in.
Anyway, thanks for the help.
--
Elliott
"Bill Renfro" wrote in message
...
The outputs are 250-3. The NTE equivlent is NTE171.
What is the problem with the set. Voltages on the outputs are about
100volts at the collector, 4.0volts on the base, and 3.5volts on the
emitter. Check the dc voltages first then you can scope the base to see
if
the correct video waveform is present. If you are missing a color,
check
the outputs from the color decoder ic (ic50). Be sure to check the CRT
for
shorts as well. Also check for bad solder joints.
Good luck,
Bill
Christian Technology
"E P" wrote in message
om...
Hello all,
I've got this 20 year old Sylvania Superset TV (model # RNE980) and
I'm trying to track down some replacement video output transistors for
it.
They are in a TO-202 package, made by Motorola, and have the following
markings:
513
K
250-3
Anybody know anything about these? Barring any suggestions, I'm
probably going to try either NTE228A or NTE171, since they're the only
video output transistors with the same pin configuration that I've
found. But I hate to stick random parts in to the TV.
Thanks
--
Elliott
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