Question about Toshiba 32A43 32" TV
The wining sound is most likely from one of the inductive reactive devices. These can be chokes or tansformers in the scan circuits or the power supply.
There are very high frequencies used in the ultra-sonic range for the switching power supply, and the transition times for the scan amplifiers and high voltage section are in the ultrasonic range. What you are hearing is something that is resonating with the magnetic fields generated by these high frequency devices, and they are making sub harmonic sounds in the audible range.
It is possible that in one of the reactive devices there are some wire turns that are a little loose, or the coil form is not very tight to the core of the device, or one of the near by metal shields is resonating from the magntic field.
There is also the possiblity that the supply voltage to one of the reactive devices is not being properly filtered by a by-pass capacitor and its structure is resonating between the normal power drive and summing with the unfiltered supply to it.
When the set is first turned on it is cold. As it operates its internal temperature will rise. There is expansion and contraction of the various parts. The reactive devices are made with very close tollerance, and their physical characteristics can change enough to allow resonance. If the fault is from a by-pass capacitor, the capacitor may have become thermo sensitive and change its characteristics with temperature.
In the case of a resonating reactive device, sometimes it is possible to fix the problem by re-inforcing the winding to the core if it is accessable. It is not always accessable to do this depending on its design. Then the solution is to change the part. If it is a shield that is resonating, this is usually easier to correct. As for any defective capacitors, these can be easily changed.
It would be best to have a very experienced TV service man look at the situation and spend the time to make a proper evaluation of what the fault actualy is.
I have had this type of problem often. I was always able to find the solution and fix it. Most of the cost of the service was from the time it took to work out the solution more so than the cost of the part, unless it was a major part such as the flyback or the deflection yoke.
Flat panel displays have switching power supplies and are subjected to similiar types of resonation faults with their power supplies.
Posted on Apr 19, 2008
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