panasonic Power Problem


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panasonic Power Problem

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Wiz
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Sep 20, 2005, 8:30 PM

Post #1 of 5 (1275 views)
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panasonic Power Problem	Can't Post

I have a panasonic TX-28G1 TV that has no picture or sound. The LED display on the front is working, but this is run from a seperate transformer to the rest of the circuitry. The main transformer between the mains part and the rest of the board reads short across all the pins on the board side(not all mains side pins read short, 3 do and the other 3 do but not between the two sets). I dont know if it is the type of transformer where the different voltages is taken off at different stages in the coils, in which case it is reading correctly. As well as this, The HOT had blown, and the base is short to the emitter by 0.6 ohms.
This does seem to be correct from my following of the tracks.
There is a voltage regulator STR54041, but I don't know how to check if it is OK. Will the HOT blowing be caused by one of these faults mentioned? And is the transformer suposed to read short across all pins? Is there something else that I'm not realising?

Oliver

rrobor
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Sep 21, 2005, 1:38 PM

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Re: [TheOW] panasonic Power Problem [In reply to]	Can't Post

The base emitter reading is correct, you are reading the drive transformer secondary. The STR is difficult, take out the horizontal output transistor then check the voltage fed to the collector connection, if none you have no B+. Check the supply, replace any small electro in the primary and check the secondary diodes for shorts, if all ok replace the str. Often the STR fails due to electrolytics and in failing, the pulse blows the horizontal

Wiz
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Sep 22, 2005, 3:24 PM

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Re: [rrobor] panasonic Power Problem [In reply to]	Can't Post

I have looked around the board, and found a diode and a coil in the primary circuit that were blown apart. I replaces these components with components from another TV.

When I turned the TV on, I get a screaching sound coming from some where around the STR or smoothing cap or drive transformer (dont want to get too close incase it blows again) Does this indicate the STR has gone? or could there be any other comonents in the area that have gone. There are a few ceramic caps in that area, but I don't think that these will have gone. Could it be a resistor? (not got round to removing them all to check them)

Thanks

Oliver

Wiz
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Sep 27, 2005, 6:53 PM

Post #4 of 5 (1223 views)
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Re: [TheOW] panasonic Power Problem [In reply to]	Can't Post

Obviously you wouldn't recomend this, and I doubt that I will do it, but as the str54041 has a few transistors in it, and overall, pin 2 is base, pin 3 is colletor, and pin 4 is emitter. Can i use a normal transistor in its place, to check if it powers up, thereby proving that it is the str that is at fault before buying a new one.

Will I destroy the TV in doing this?

Wiz
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Oct 1, 2005, 1:36 AM

Post #5 of 5 (1196 views)
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Re: [TheOW] panasonic Power Problem [In reply to]	Can't Post

what will happen to the TV if I do this??

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