need help diagnosing TV problem - JVC AV 27920
 

If you are going to do service on this set, I would highly suggest to
invest in the service manual, to be able to follow up on what is going
on. The first thing to do before speculating on failed parts or a
failed IC, is to take the necessary voltage readings, and evaluate the
waveforms reaching the vertical output IC. This way you will be able to
determine if the IC is possibly defective or not.

You may find it to be more reasonable in cost to have an experienced
shop service the set for you. When buying parts, schematics, and any
necessary tools to guess at a fault condition, this can get rather
expensive for no reason. There are also strong safety issues involved
when doing TV servicing.

--

Greetings,

Jerry Greenberg GLG Technologies GLG
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"dino" wrote in message
...
Hi everyone,

I picked up a seemingly dead 27" JVC tv (AV-27920) and am trying my luck
in
attempting to fix it. The TV is dated May 1998. I have no prior
knowledge
of the TV's behavior before completely dying. Right now a consistant
event
takes place - when the TV is turned on, a blurry white horizontal line
appears in the center of the screen and then disappears quickly -- black
screen after that. The sound works; power supply (134 volt regulator)
checks ok. When the TV is turned off, I see a small round white circle
(around 2" in diameter) appear on the center of the screen for a brief
period of time.

I did minor troubleshooting so far however I am inexperienced with
reading
TV malfunctions. Would this symptom (horizontal line only showing up
once
at turn on time) be consistent with the guess that the vertical
deflection
IC is out?

I researched a bit on the internet about this particular series of JVC
tv's
and everyone points to LA7832 (IC for vertical deflection output). I
changed ~8 electrolytic capacitors around the vert section to see if any
change took place and I did not notice anything different. Would it be
correct to assume that this described behavior indicates a vertical
deflection IC problem?

Thank you for your help,
-dino

need help diagnosing TV problem - JVC AV 27920
 

Sounds like the vertical circuit is dead, triggering the TV's shutdown circuit,
or at least blanking the video

need help diagnosing TV problem - JVC AV 27920
 

First, make sure you have about 25v on pins 6 and 3 of the LA7832. If missing,
trace back from pin 6 to find an open resistor that should be about 1.2 ohm,
then check the diode feeding the resistor for a short. If it's not shorted
replace the LA7832, (use a LA7833 for replacement), and the resistor. If 25v is
present on the IC, just replace the LA7832. (use a LA7833 instead of a 7832).
Make sure one of the caps you changed is the one between pins 3-7 of the chip.
This is the one that causes the chip to fail.
Ron