G
Glenn
- Jan 1, 1970
- 0
I have a dead colour TV that I'm finally having a go at fixing - no
expert on these things though.
The chopper transistor on the switch mode supply has shorted out.
Replaced it and same again (very quickly fails), so there is a problem
somewhere. I have a couple of questions:
1. Anyone know a good online description, in detail, of the operation
of these supplies. For example, the feedback from the output side of
the supply that apparently controls the chopper transistor is through a
single four pin IC that I can't identify. I suspect it may be an
optoisolator but not certain. It carries markings OA . P621 . 4 G.,
The manufacturer logo looks like a "T", but don't recognise it (its not
an SGS Thomson logo).
2. I can think of at least two possible generic causes of the failure:
a) Failure somewhere in the actual TV circuit that is causing
excessive current drain and overloading the power supply, eg horizontal
output transistor (but this looks OK).
b) Failure in the switchmode supply itself such that the chopper
transistor is forced permanently on, or is being driven at a much
higher duty cycle than it can handle. Are there any other
possibilities, and testing strategies?
Cheers
Glenn
expert on these things though.
The chopper transistor on the switch mode supply has shorted out.
Replaced it and same again (very quickly fails), so there is a problem
somewhere. I have a couple of questions:
1. Anyone know a good online description, in detail, of the operation
of these supplies. For example, the feedback from the output side of
the supply that apparently controls the chopper transistor is through a
single four pin IC that I can't identify. I suspect it may be an
optoisolator but not certain. It carries markings OA . P621 . 4 G.,
The manufacturer logo looks like a "T", but don't recognise it (its not
an SGS Thomson logo).
2. I can think of at least two possible generic causes of the failure:
a) Failure somewhere in the actual TV circuit that is causing
excessive current drain and overloading the power supply, eg horizontal
output transistor (but this looks OK).
b) Failure in the switchmode supply itself such that the chopper
transistor is forced permanently on, or is being driven at a much
higher duty cycle than it can handle. Are there any other
possibilities, and testing strategies?
Cheers
Glenn