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philips tv shorts horizontal even when changed

 
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abr
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PostPosted: Tue Jan 27, 2009 8:49 pm    Post subject: philips tv shorts horizontal even when changed Reply with quote

I have a philips tv , the Horizonyal transistor ( BU508F) was shorted and i just changed it but it was shorted even it didn't stay for seconds & i just changed another original transistor but again it's shorting every new changed transistor, so what couold be the problem plz
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jts1957



Joined: 24 Nov 2008
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PostPosted: Tue Jan 27, 2009 10:05 pm    Post subject: Reply with quote

Check Horizontal Drive circuit.
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torbjorn



Joined: 07 Jun 2007
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Location: Sweden

PostPosted: Wed Jan 28, 2009 12:33 pm    Post subject: Reply with quote

Also, check the flyback capacitor(s), and check all circuitry around the horizontal output for bad solder joints, overheated components, shorted diodes etc. Make sure that there are no signs of overheating or arcing at the connector to the deflection coils.

If the tv has no horizontal driver transformer but the driver stage is capacitively coupled to the base of the output transistor, then you should suspect all electrolytics in or near the driver stage.

Also, cases are known where the horizontal output transistor has failed due to the horizontal oscillator being much off correct frequency (a common fault on some Daewoo chassis from the late 80's, where a capacitor in the oscillator circuit often got open circuit and caused it to oscillate at several hundred kHz instead of 16 kHz).

A common rule that if the output transistor fails due to bad drive, it usually is very hot when it just has failed. If it fails due to too high collector voltage (bad flyback caps or similar faults), then it does not get hot when it fails.
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LJ



Joined: 09 Dec 2008
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PostPosted: Wed Jan 28, 2009 2:22 pm    Post subject: Reply with quote

Also check for B+ flyback voltage, maybe over voltage.
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PostPosted: Wed Jan 28, 2009 7:51 pm    Post subject: Reply with quote

thanks for the help , but can u plz give me an idea of the horizontal drive & what components does it contain. & the voltage reaching to the collector of the HOT is 148v.
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jts1957



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PostPosted: Wed Jan 28, 2009 8:34 pm    Post subject: Reply with quote

So you want specifics...
Then "you'll" have to be more specific.
Model / Chassis ?
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