Re: Panasonic TV - TC-25V30R - fuse blows repeatedly

From: Jerry G. (jerryg50_at_hotmail.com)
Date: 06/02/04 

Date: Wed, 2 Jun 2004 17:01:33 -0400

All the advice you have been getting from the others is very true. The power
supply would have to be first serviced, and then the horizontal output
stage. There are other components that are off value, and must be replaced.
There is also a chance that the flyback transformer has been damaged,
especially that the HOT was shorted. If there is even one shorted turn in
the flyback, it can cause your description. But, you can be sure that there
is a lot more damage than just the flyback.

The people who service these sets professionally, go through the proper
training and theory of how these sets work. The factory service techs are
extensively trained on the particular models that they will be servicing.
These sets are fairly complex, and can sometimes be a challenge for even the
most experienced techs.

In many cases it is not cost effective to service the set yourself, unless
you are properly trained, and have the necessary test gear to work on the
set. Infact, many of the smaller shops will jobber out the more complex
problems to the factory service people.

I would think that after changing the various blown components a number of
times and also considering the purchase of the service manual, you are
probably approaching the cost of having an authorized service tech service
the set for you. This is not even accounting for your time.

In the many years I have been involved in the service business, I found it
very rare for the non experienced to be able to repair any of the complex
faults in these sets. I have only seen them succeed with the more simple
faults, such as changing a switch or control, or a simple part that they
were told to change that is a standard type of problem. 

-- 
Jerry G.
=====
"W.i.k.i.M.a.n" <wikipediholic@yahoo.com> wrote in message
news:e8ca9c8.0406011905.26d1a866@posting.google.com...
Hi,
I had my tv repaired some time ago. All the functioning
was fine but the technician had replaced the main fuse with a
thick wire and I started using the tv without knowing about that.
Recently, it went bad again. I decided to check it myself. I opened
the casing and instantly spotted a broken/open resistor 3.3 ohm, 15W.
I replaced it and powered the set. It started but after about 5/6
seconds went down with explosion and lightning. The same resistor
broke open again. At this time I spotted the thick wire at the
main fuse holder.
I bought the tv's circuit diagram, read SER FAQs, and went on to
check for any bad power transistor in the supply section (since power
supply input read 50 ohms indicating that bridge or posistor is not
the problem IMO). HOT was good but another one, C4706, high voltage
switching transistor in the regulator section of SMPS, was bad, both
B-E and C-E were shorted.
I replaced the resistor, C4706 transistor, and fuse (T4.0A), and
powered the set. It ran for about 7/8 seconds, screen was brightened
white with a black horizontal line in the middle. And then it turned
off again with explosion and lightning. I rechecked, this time only
the fuse was blown.
Being an electrical engineer, I'm not considering an option to get it
repaired by someone else. For this, I need the following information:
- Is this start-up scenario typical with some common cause and
remedy?
- I think of first confirming if the SMPS is good, and for this I
should disconnect all other circuit (all load of SMPS) and check if
fuse still blows, and if it doesn't, are the output voltages correct
(according to the diagrams, SMPS should give 140v, 12v, and 5v DCs)?
- Any other ideas of how to proceed?
Thanks in advance,
W.i.k.i.m.a.n

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