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

From: Asimov (Asimov_at_-removethis-bbs.juxtaposition.dynip.com)
Date: 06/02/04 

Date: Wednesday, 02 Jun 2004 16:32:08 -500

Hi,

Use a 100 watt lamp in series with the powerline next time to limit
the current in case of a problem. In my opinion if the screen filled
up white this means you have both deflection and HV. The black bar is
still an unknown at this point.

Now the question may be what about the audio section, the video, etc?
Is the regulated supply too high? For example 150 volts on the 130
volts line. This could make the HV go way high and then some xray
safety feature is causing the mains fuse to blow. Try disabling the
HOT and see if some other circuit is drawimg too much power. Work at
diagnosing the problem 1 step at a time. Start by checking the
electros around the horizontal driver and HOT.

 "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

... You mean 15" sparks are SUPPOSED to come out of this thing?!?

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