[TechAssist] RCA proj. TV P46734BA, Chassis PTK178LA finally FIXED
- From: Gary McCartney <gary@xxxxxxxxxxx>
- To: techassist@xxxxxxxxxxxxx
- Date: Thu, 23 Jun 2005 23:31:58 -0400
RCA proj. TV P46734BA, Chassis PTK178LA finally FIXED (after 5 years!)
First, an explanation:
Back in 2000, my friend's TV (above mentioned model) was acting up such
as turning off after a few minutes of use. He bought it with extended
warranty. At that time, ext. warr. was in effect so he took it where he
bought it and they had their authorized RCA depot come get it. Six weeks
later they said warranty would not be honoured because they found traces
of a liquid and some mouse droppings in the chassis. They estimated
$700.00 to fix. Friend refused and they charged him $100.00 for the
parts they put into it. (HOT, etc.)
I got the set to fix for him. He hasn't needed the TV since then because
he has been renting small houses where theres not enough room for a big
TV. Now he is ready to move into his brand new house he just built.
About time I finish the repair eh? I've only been daddling with it on
and off whenever I'm not busy on the bench, and then only when in the mood.
When I first worked on the set, it would click 3 times but not start up.
I suspect this condition may have been born with the help of the first
tech who worked on it. Here are the events, by memory so there may be
other things tried or whatever during the process.
- First I cleaned off all signs of corrosion and dirt from the boards.
-Pulled flyback anode from HV splitter but didn't solve.
-found tip to check for cracks in trace around C1474 on I/O board
because it sticks out horizontally a ways. Yes there were cracks and
fixed them but no help.
- found R4912, the trim POT for B+ adjust to be open. Changed it with
regular trim pot, not the RCA kit. Also changed U4101, PWM controller
which by memory is a UA3843. May have also changed a few associated
parts but can't remember. THis made the power supply react differently
but can't remember how.
- Used Chipper Checker to figure out why the shut-down. It told me
problem could be in the audio section. Yes, I found U1600 stereo decoder
IC (CXA1734S, RCA# 225700)to be corroded and defective. Replaced but
still not starting up. Chipper checker no longer saw this error.
-I decided to try a new eeprom and micro kit because there was some
corrosion on the micro and I suspected eeprom anyways. RCA # 212119. Set
reacted differently but still not starting correctly.
-next I seem to remember soldering the power transistors on the heatsink
along the front of the chassis. Finally, the set fires up but after a
few seconds, I see smoke coming from the vertical output IC TDA8132.
Replaced it and now the set fires up and runs.
- Hissing sound from the HV splitter. I removed all leads and install
new gaskets and add silicone grease. No more hissing.
- Adjust B+ pot R4912 for 135V B+ at cathode of CR4110. Check X-ray
protection test- ok.
- test run and check for sound output and check for tuning of channels
and also check video input- all ok.
- now set is ready to go back to the cabinet for final alignments.
--
Thanks to all who helped me with this repair through the years.
Gary McCartney
McCartney Electronics
Guelph Ontario Canada
Est. 1984
email: gary (at) number63.ca
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