Interesting case: Toshiba 32AV502R Tuning(?) issue

[randtek]

I work on a lot of TVs. Not many of them catch my attention as particularly interesting, but this one did.

TV worked fine from all inputs EXCEPT tuner. When tuner input was selected. TV would continuously cycle off and back on *AS LONG AS AN ACTIVE CHANNEL WAS TUNED IN*. If TV was turned to an inactive channel, or the cable was disconnected, it would stay on and work fine. Power supply voltages tested within tolerance, but due to the cycling, I could not get a really good voltage reading when it was failing. I replaced the main board, and unit seemed to be working fine. It completed it's autoprogramming sequence, and was not cycling anymore when receiving a channel. I left the TV test playing, and returned about 20 minutes later to a completely dead TV. A few quick continuity checks found a bad main fuse, and one diode of a diode bridge pack was shorted. Replacing these components restored the TV to full operational status, and it has not failed again. But now my technician curiosity was piqued.

I reinstalled the original main board, and was not completely surprised to find that it was now working too. So the final conclusion was that the TV originally had a slightly leaky diode bridge pack. This was limiting the current able to be delivered through it. The original main board was operating at a critical curent level, just below the threshold of what the power board could deliver, due to the compromised diode bridge. When it received a channel, it was going just over the threshold, and the TV would restart itself. When the new main board was replaced, differences in tolerances allowed it to operate fully, but the extra current load caused the diode in the bridge pack to fail completely, thus opening the fuse.

[tom66]

Re: Interesting case: Toshiba 32AV502R Tuning(?) issue

That is a strange one. Does the power supply in the TV have a PFC section, or is it just rectifying AC?

[Tvbob]

Re: Interesting case: Toshiba 32AV502R Tuning(?) issue

Hey, Randtek. How is that Toshiba doing? I have the same Toshiba 32av502r with the power cycling problem. I checked the caps and resoldered some connections on the power supply board.The set worked for 3 weeks,now it has started to act up again I was in the market for a main board until I read this post. Thanks

[rama9998]

Re: Interesting case: Toshiba 32AV502R Tuning(?) issue

Randtek, Could you throw some light on where to locate the diode bridge pack? Is this in the main power supply board? I did replace some working capacitors but have the same problem. The tv starts recycling only when I connect an input through HDMI.. If no input is connected, the Tv remains on..

I am not that very well versed, but can do testing and replacing components, so any specific details you can give, it will be helpful.. Thanks in advance..