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Sharp DA-50W chassis, problem with horizontal output stage

 
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torbjorn



Joined: 07 Jun 2007
Posts: 370
Location: Sweden

PostPosted: Thu Jun 07, 2007 8:24 am    Post subject: Sharp DA-50W chassis, problem with horizontal output stage Reply with quote

Horizontal output transistor Q601, BUH515 was shorted and resistor RA611 showed signs of overheating. Both those components were replaced and several bad solder joints repaired. When switching on the set, it worked normally for 1-2 minutes, then Q601 failed again. Q601 does not get hot prior to failing. A suggestion from another forum was that this could be caused by insufficient base drive to Q601 due to a bad C607. This capacitor has been replaced without success.
A strange thing is that the set runs so well before Q601 fails. If it had been, for example, a flyback capacitor problem, then the picture width would not have been correct and it would probably have shown E/W distortion.
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bbp1



Joined: 04 May 2007
Posts: 22

PostPosted: Sat Jun 09, 2007 6:42 am    Post subject: LOT failure Reply with quote

Check/change LOPT!I assume you have checked everything elseB+, electros, djs etc. And not to forget yoke. Confused Confused
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