Choke coil buzz on plasma

[The_Todd]

Hey guys,

So I fixed this plasma, and everything is fine except for a high pitched buzz witch I have narrowed down I think to a Radial choke. (600v rated on the side) this is located on the main power board, is is more notable when the TV is in standby, is is sitting near the secondary power side.

So my understanding of chokes and inductors in general is still sketchy but I have a few questions.

1. is there anything else that could be causing the coil to vibrate? like a tiny capacitor that is playing up, mosfet dying ect?

2. can i replace with another type of Coil like Toroidal ect. that may be less noisy and what effect can that have on the circuit?

thanks.

[tom66]

Re: Choke coil buzz on plasma

It's pretty normal for plasma TVs to buzz gently in operation. This is due to the fact that the screen is rapidly pulsing about 600 times a second to produce the image on the screen.

If you can hear the buzzing from a normal distance, once the case is on, then that is something worth investigating, otherwise, it's not really something you can fix.

[The_Todd]

Re: Choke coil buzz on plasma

Hmm.... upon more investigating In stanby mode,

if i disconnect the main logic board, it goes dead silent?
the main board has a lot of SMD silver cap electro caps and some conductors.
(and interestingly a SONY brand processor, this is a Samsung P50P91FD)

So if we say that for some reason that something is using more power then it should on standby, perhaps a cap or something leaking to ground. could this cause slightly more draw then usual thus making the power supply create a slightly elevated PWM supply witch may be creating just the right conditions to create the resonance that we can hear?

and another question, for the standby voltage, what generally are acceptable limits for the voltage with and without load? (assuming its safe to Run standby without load)

cheers,

[tom66]

Re: Choke coil buzz on plasma

if i disconnect the main logic board, it goes dead silent?

Of course...no load, no noise. You're hearing coil whine, it's *completely* normal.

(and interestingly a SONY brand processor, this is a Samsung P50P91FD)

Sony makes silicon for lots of companies. Sharp makes the plasma subframe processor found in most LG sets. Samsung makes 50% of Apple's iPhone CPUs. Not uncommon. Depends on who has the IP/patents or the best engineers for that part of a system, Sony have the professional video market so a lot of expertise in area of video processing.

So if we say that for some reason that something is using more power then it should on standby, perhaps a cap or something leaking to ground. could this cause slightly more draw then usual thus making the power supply create a slightly elevated PWM supply witch may be creating just the right conditions to create the resonance that we can hear?

Very unlikely. Would have to draw a lot of current. Bad cap might cause buzzing due to instability on PSU output.

and another question, for the standby voltage, what generally are acceptable limits for the voltage with and without load? (assuming its safe to Run standby without load)

It's safe, generally Samsung use 5.2 or 5.3V outputs, anywhere from 4.8V to 5.5V will usually be okay.