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tv: vertical jitters

H

Herb

I have an Apex 19" TV here, only three years old. It's been occurring
that the picture gets vertical jittering (and looks slightly washed
out) for maybe half a minute - then it gives one big jump and then
it's okay for a long while.

Also, symptoms are progressing. From time to time, the picture gets
reduced down vertically, so that it looks like letterbox format and it
is also very washed out. Then it gives one big jump and then it's okay
for a while.

The newest thing is that sometimes when I turn it on, it displays only
a blank screen - no picture and no sound whatsoever. I have to
repeatedly turn off/on until it works again.

Is this a failing capacitor? How can I proceed to try and fix it?
Thanks.
 
J

James Sweet

Herb said:
I have an Apex 19" TV here, only three years old. It's been occurring
that the picture gets vertical jittering (and looks slightly washed
out) for maybe half a minute - then it gives one big jump and then
it's okay for a long while.

Also, symptoms are progressing. From time to time, the picture gets
reduced down vertically, so that it looks like letterbox format and it
is also very washed out. Then it gives one big jump and then it's okay
for a while.

The newest thing is that sometimes when I turn it on, it displays only
a blank screen - no picture and no sound whatsoever. I have to
repeatedly turn off/on until it works again.

Is this a failing capacitor? How can I proceed to try and fix it?
Thanks.


When capacitors start to fail, the problem usually gradually improves as
the set warms up. In this case I'd be more inclined to suspect solder
joints or a semiconductor. A can of freeze spray might be helpful in
diagnosing it.
 
I

ian field

Herb said:
I have an Apex 19" TV here, only three years old. It's been occurring
that the picture gets vertical jittering (and looks slightly washed
out) for maybe half a minute - then it gives one big jump and then
it's okay for a long while.

Also, symptoms are progressing. From time to time, the picture gets
reduced down vertically, so that it looks like letterbox format and it
is also very washed out. Then it gives one big jump and then it's okay
for a while.

The newest thing is that sometimes when I turn it on, it displays only
a blank screen - no picture and no sound whatsoever. I have to
repeatedly turn off/on until it works again.

Is this a failing capacitor? How can I proceed to try and fix it?
Thanks.

The combination of jitter and washed out picture might suggest a bandwidth
or gain problem in the IF circuitry, but the intermittent aspect of the
symptoms you go on to describe suggest more likely failing of lead-free
solder in the V-O/P stage, a re-work of the soldering in this area is
probably the quickest and easiest thing to eliminate a possible cause. If
that doesn't cure it, warming various areas of the panel with a hairdryer as
already suggested might give a clue to capacitors with ESR problems, before
I bought an ESR meter I had devised a variety of means to weed these out, in
PSUs faulty caps often run hot while smaller caps in signal stages were
often sensitive to gently twisting them on their leads. One very useful
instrument I still keep handy is a Steinel continuity checker, it has an
inverse parallel pair of LED, a battery and a thin film PTC thermistor so
the test current starts briefly high and decays to a suitable value for one
or the other of the high efficiency LEDs, With the suspect cap out of
circuit, the tester would give a short flash as the cap charged - then if
the button was released the other LED would flash as the cap discharged -
caps with ESR problems caused the flash to visibly "ramp up" before decaying
again.
 
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