Hello.
I recently bought a store return Samsung 32" LCD TV at a great discount.
The TV set is great and perfect in every detail except one:
After about an hour, a loud whistle noise starts coming out of the back of the set.
This condition is all over the internet, with Samsung replacing coil chokes or power supply boards all over the country. The power supply boards are cheap and readily available. I even managed to track down the replacement coil choke.
Removing the back cover and listening around with a soda straw revealed a noisy choke coil on the power supply board. All of the caps are Samwha WL and WB low and ultra-low impedance.
Replacing the coil reduced the noise but did not eliminate it.
Replacing the caps with UCCs and Rubycons had no effect.
While the board was out, I noticed that the inductor does not appear to have a primary capacitor! The circuit trace goes directly from the switching transistor to the coil. The trace leaving the coil does have a cap on it.
Could Samsung be asking too much of a coil to dampen all this bumpy electricity? Apparently, because the coil sure doesn't like it very much and doesn't mind saying so.
I was wondering if drilling some holes and adding a capacitor would be a good idea. Probably not, as I lack the understanding and talent to choose a suitable capacitor rating and type.
I also noticed that this board has an "A" revision and a "B" revision board is available. Maybe I should just get the newer version? It's not too expensive, the TV set is astounding and the the price I paid was way too cheap not to keep.
Any ideas about this circuit design? Or about my observations?
Thanks for any ideas,
Keri
added: The coil in question is a wire wound toroid with heatshrink tubing covering it. The original coil gets very hot, the new one less so.
I recently bought a store return Samsung 32" LCD TV at a great discount.
The TV set is great and perfect in every detail except one:
After about an hour, a loud whistle noise starts coming out of the back of the set.
This condition is all over the internet, with Samsung replacing coil chokes or power supply boards all over the country. The power supply boards are cheap and readily available. I even managed to track down the replacement coil choke.
Removing the back cover and listening around with a soda straw revealed a noisy choke coil on the power supply board. All of the caps are Samwha WL and WB low and ultra-low impedance.
Replacing the coil reduced the noise but did not eliminate it.
Replacing the caps with UCCs and Rubycons had no effect.
While the board was out, I noticed that the inductor does not appear to have a primary capacitor! The circuit trace goes directly from the switching transistor to the coil. The trace leaving the coil does have a cap on it.
Could Samsung be asking too much of a coil to dampen all this bumpy electricity? Apparently, because the coil sure doesn't like it very much and doesn't mind saying so.
I was wondering if drilling some holes and adding a capacitor would be a good idea. Probably not, as I lack the understanding and talent to choose a suitable capacitor rating and type.
I also noticed that this board has an "A" revision and a "B" revision board is available. Maybe I should just get the newer version? It's not too expensive, the TV set is astounding and the the price I paid was way too cheap not to keep.
Any ideas about this circuit design? Or about my observations?
Thanks for any ideas,
Keri
added: The coil in question is a wire wound toroid with heatshrink tubing covering it. The original coil gets very hot, the new one less so.
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