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No Raster with Sound ,Panasonic Tv TC-29V50R
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Jujeet



Joined: 25 Mar 2007
Posts: 22

PostPosted: Tue Jan 20, 2009 2:32 pm    Post subject: No Raster with Sound ,Panasonic Tv TC-29V50R Reply with quote

I have a panasonic tv which keeps shutting down.There is sudden burst of horizontal drive at Q501 when you on initally.But goes off with 140 volt present at collector of Q501.I have replace the LOT.
I am not able to get my 13 volt at Q802 collector which source IC804 and IC805.Its about 8 volt at collector of Q802 when it shutdown.

Has anyone got any idea how to go about troubleshooting this kind of faults.

Best Regards[/code]
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jts1957



Joined: 24 Nov 2008
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PostPosted: Tue Jan 20, 2009 3:38 pm    Post subject: Reply with quote

Voltages at base & emitter of Q802? Other SMPS secondary voltages?
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Jujeet



Joined: 25 Mar 2007
Posts: 22

PostPosted: Wed Jan 21, 2009 4:04 pm    Post subject: No Raster with sound, Panasonic TC7-29V50R Reply with quote

Q802 emitter is 84.6volt,base is 84.2 volt . It is not conducting to give me 13volt at Q802 collector.B+ 140volt is present at IC803,+15volt is present at connector P82. As in the circuit diagram Q806 base is controlled by pin 29 of IC1102 when this goes high Q802 starting conducting thus providing +13volt. Initially when you ON the Tv set pin29 goes high, Q802 turns on providing +13 volt.But what happening is that it snap to low level,thus pulling the +13volt rail to 8volt.Its not enough to power the 3pin regulators.
Please advice on these matters.

Thank you.
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jts1957



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PostPosted: Wed Jan 21, 2009 9:23 pm    Post subject: Reply with quote

I hope you mean 15 volt is present at P83 (NOT P82), otherwise I'm looking at the wrong schematic.
Could be an excessive load on or defective 5 volt source?
What happens to 13 volts when IC804 is disconnected from foils? Also could try "floating" Pin #1 of P82.
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Jujeet



Joined: 25 Mar 2007
Posts: 22

PostPosted: Thu Jan 22, 2009 4:03 pm    Post subject: Reply with quote

I have disconnect the 13volt to IC804 input pin. It reads 35.8volt and pin 2
reads 4.99volt with foil removed.Is the input voltage of AN7805MO5LB too high?With my +5volt load completely removed,its reads 35.8volt at pin1 and pin 2 reads 4.99volts Do you reckon that 7805 is faulty?


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LJ



Joined: 09 Dec 2008
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PostPosted: Thu Jan 22, 2009 4:34 pm    Post subject: Reply with quote

Maybe it's not faulty of 7805, try to make sure there's no component at the 5V loading getting short, if there's an "almost" short component at loading, it could be a very heavy loading for 7805 and could make 5V output drop.
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jts1957



Joined: 24 Nov 2008
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PostPosted: Thu Jan 22, 2009 6:49 pm    Post subject: Reply with quote

If memory serves, max. voltage for most three-terminal regulators is 35 volts (7805 min. voltage = 7ish).
What IS voltage at IC804 Pin #2 with everything connected? And is that device getting HOT? If so, something on 5 volt line is leaky or shorted.
Have you checked ALL semiconductors between T801 secondary and the three connectors at the right edge of the schematic?
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PostPosted: Fri Jan 23, 2009 2:45 pm    Post subject: Reply with quote

Hi there. P83 pin 1 which was purpose to read as +15 volt reads 8.46volt.
Disconnecting L822 restored the +13volt t input to 7805 regulator.
The +15volt rail is loaded down.
Any idea which likely component is pulling it down.
I am working on it.

Thanks you very much guys
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jts1957



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PostPosted: Fri Jan 23, 2009 3:10 pm    Post subject: Reply with quote

You fool! Laughing You said 15 volts was OK, although you had said it was on a different connector.
The usual: follow the short ... measure resistance on 15 volt foil follow foil until it splits - lift one component, jumper, etc. - measure both sides - follow whichever side is lower until defective part is reached.
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jts1957



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PostPosted: Fri Jan 23, 2009 3:23 pm    Post subject: Reply with quote

IC805?
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