Sharp C-1410 no power (smps issue)

[vol.2]

Originally Posted by ostlar

Yes the short is gone after removing the flyback, I tested the resistors and capacitors in the circuit and they were fine.
I'm probably just going to send it with a new flyback and hope for the best.

FWIW, when I said that you should check the short condition with the flyback out of circuit, I didn't mean you should test the components.

I meant that you should verify that all short conditions are gone in the circuit by testing continuity to ground from the various points in the circuit that you initially noticed the short condition.

If you still have a weird reading, then you've still got a short present somewhere, regardless if your components test out okay in the immediate area.

[ostlar]

Originally Posted by vol.2

FWIW, when I said that you should check the short condition with the flyback out of circuit, I didn't mean you should test the components.

I meant that you should verify that all short conditions are gone in the circuit by testing continuity to ground from the various points in the circuit that you initially noticed the short condition.

Yes, that's exactly what I did. I have verified that all the short conditions are gone in the circuit by doing the same measurements as I did initially. The fault is definitely in the flyback.

I'll have to wait for the new flyback to test it, and I will report back on how it goes.

[vol.2]

Originally Posted by ostlar

I'll have to wait for the new flyback to test it, and I will report back on how it goes.

Okay cool cool. Yes, I would be interested to know how things go from there.

[ostlar]

Good news, it is now alive and well. New flyback did the trick, and it works as before.

Did a thermal image of the board, and nothing stands out except for a resistor that is hot (144°C), R623 which is feeding the horizontal circuit that I have been troubleshooting. The voltage drop over the resistor is only 2,2V, so it should only dissipate around half a watt of heat. Resistor in question is rated at 3W. The resistor is elevated quite a bit from the board, so it is expected to be hot. The max operating temperature of 3W resistors are usually from 150°C to 200°C.

I will diagnose a bit further, because I am not entirely sure the flyback died by itself. Could be driven too hard and the heat made it short out internally. The flyback itself and other components does not show any abnormal temperatures. Maybe I am a bit paranoid, but it is better to be safe than sorry.

Edit: just realized I have two other TVs now with the same chassis, so I will do a thermal image of those to compare.

[Username1]

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Good Work! - As far as temps go on the resistor.... You have an identical tv for that.


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