Goodmans TV 14RC

[SPal508596]

I've got this tv set which works fine but the power supply makes alot of noise.
The sound in the power supply varies as the picture scene moves. I've checked
the voltages in the power supply and they are all normal. I then connected a
60W bulb to the Line output stage and it produced 103V but still the power
supply was making noise. What tests should I perform to find the cause of this
noise?

 

[Jerry G.]

Depending on the nature of what is going on, there are a few things in
retrospect. Sometimes these supplies get noisy when some of the decoupler
caps start to go high in ESR. You can use an ESR meter to test them or
change the caps to test. Or you can run the set on an isolation transformer
and use a scope to check the performance of the caps while the set is
running.

The other thing it may be is that the switching power driver transformer, or
some other reactive device may be resonating. When there is a greater load
on the supply due to brighter picture content, the current is higher, thus
making the windings in the transformer, or reactive device have a stronger
reaction in their magnetic field. With age, some of the windings may loosen
up a bit, thus causing this type of characteristic to occur.

It is also possible to have something near by to the switching power driver
transformer that is resonating to the field created by this device. A metal
piece near by, or some other type of component near by may be in resonance,
and thus mechanically ringing.

I have seen flybacks, yokes, and various types of reactive components to in
to resonance. Sometimes these faults can be difficult to resolve. With
experience, and spending the time on solving this, it can be serviced. Some
of the TV models do this to some degree, right out of the factory when new,
and it is a characteristic of design.

--

Greetings,

Jerry Greenberg GLG Technologies GLG
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"SPal508596" <spal508596@aol.com> wrote in message
news:20040219154558.03317.00000009@mb-m23.aol.com...
I've got this tv set which works fine but the power supply makes alot of
noise.
The sound in the power supply varies as the picture scene moves. I've
checked
the voltages in the power supply and they are all normal. I then connected
a
60W bulb to the Line output stage and it produced 103V but still the power
supply was making noise. What tests should I perform to find the cause of
this
noise?