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vestel 11AK36 A8 TV - PSU not starting

This 14" 11AK36-A8 tv apparently 'just went off.' there was evidence of a short near the mains inlet, on the print side of the pcb - probably a strand of wire or blob of solder from the time of manufcture had been the cause. checked rectifier, removed PTC in case, replaced fuse. Set dead. 0v at psu o/ps.

checked the obvious in psu primary, no shorted diodes or open resistors. Removed secondary diodes including HT line.

schematics here (5m). Psu is on page 24.:

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FULL.pdf

...not identical but the main aspects are the same.

300v present across mains capacitor, and at R821 (safety) and collector of Q801. 25v present at c811, suggesting the uPc of the PSU has power.

I don't know where to look now. My next step would be to change the uPc UC3843, but I don't think I've ever seen a case where the chip went on its own...

I should probably have tossed this aside by now but I'm just keen to satisfy my curiosity. So I'm all ears. cheers, B.

Reply to
b
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On Fri, 27 Aug 2010 05:05:57 -0700 (PDT), b put finger to keyboard and composed:

If the voltage at C811 is 25V, then one would expect that one or more of D840 (15V zener), D839 (signal diode) and Q809 are open. AISI, the combined voltage drop across all three components should be around

16V.

- Franc Zabkar

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Please remove one 'i' from my address when replying by email.
Reply to
Franc Zabkar

The link doesn't seem to get you direct to the schematic. Seems to want a login from the home page ?

As for '3843s, I have had them go faulty on their own on other Vestel PSUs, but I agree, it's rare. Have you ESR checked any small primary-side electrolytics ? Is there anywhere else I can get a squint at the schems, or can you mail the pdf to me direct ? I do quite a lot of switchers, and used to do a lot of Vestels from bigger LCD TVs, so I might be able to offer an insight or two ...

Arfa

Reply to
Arfa Daily

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thanks. try this link:

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I got this from eserviceinfo originally, I think. Re: electrolytics, besides the mains filter cap I think there's only the one I mentioned (c811) cheers Ben

Reply to
b

On some of the Vestel supplies that I've worked on, I have had problems with the high voltage polyester caps going open. That 47nF 630v one, C812, would be a prime one to check, particularly if it's a bright blue 'boxy' one, rather than a brown epoxy coated type. I'll have a bit closer look tomorrow.

Arfa

Reply to
Arfa Daily

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thanks, will follow that up sometime in the next fortnight cheers, B.

Reply to
b

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