Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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RubbishRat
 
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Default fuse blows


"Brett" wrote in message
om...
I have an Orion TV, model #TV1934. Can't find the chassis number. Set
blows the fuse when plugged in. Found 2 bad diodes in power supply,
replaced them, plugged set back in, and BAM, blown fuse and same 2
diodes toast. I checked the HOT, and power regulator, both are fine. I
unplugged the degauss coil, and the set won't blow the fuse, but won't
power up either. I can't find a short anywhere. There is a component
marked TH501 tied to degauss plug. What is this component? I megged it
and shows no resistance. Please help. Almost forgot, the set was hit
by lightening, but no apparent damage. Please help.


TH501 is there to remove power from the de-gauss coils a short time after
power up and is not a suspect here. It will show no resistance initially.
The two diodes are probably the main feed rectifiers to parts of the set
that are themselves damaged (maybe the vert or hor osc for instance ).
Lightning strikes can do extensive damage to delicate critical parts like
the microprocessor or regulator. I think this set needs the attention of an
experienced troubleshooter.
Pete


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Sam Goldwasser
 
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Default fuse blows

(Brett) writes:

"RubbishRat" wrote in message ...
"Brett" wrote in message
om...
I have an Orion TV, model #TV1934. Can't find the chassis number. Set
blows the fuse when plugged in. Found 2 bad diodes in power supply,
replaced them, plugged set back in, and BAM, blown fuse and same 2
diodes toast. I checked the HOT, and power regulator, both are fine. I
unplugged the degauss coil, and the set won't blow the fuse, but won't
power up either. I can't find a short anywhere. There is a component
marked TH501 tied to degauss plug. What is this component? I megged it
and shows no resistance. Please help. Almost forgot, the set was hit
by lightening, but no apparent damage. Please help.


TH501 is there to remove power from the de-gauss coils a short time after
power up and is not a suspect here. It will show no resistance initially.
The two diodes are probably the main feed rectifiers to parts of the set
that are themselves damaged (maybe the vert or hor osc for instance ).
Lightning strikes can do extensive damage to delicate critical parts like
the microprocessor or regulator. I think this set needs the attention of an
experienced troubleshooter.
Pete


Looking at the circuit board, if TH501 does not remove power as it
should from the coils, there will be a dead short between main power
supply when set is plugged in. The degauss should remain inactive
until set is turned on right? I don't have the schematic yet, but
can't figure out why unplugging the degauss coil prevents fuse and
diodes from blowing. I re-checked the Horizontal output transistor out
of circuit. It checked good with a transistor tester, but when megged,
it showed very little resistance between emitter and base regardless
of polarity. Looks like a short here. I ordered a new HOT. Again, will
unplugging the degauss coil prevent set from power up/blowing fuse?
Thanks again for any help. Very green beginner.


If removing the degauss coil prevents the fuse from blowing, either
the problem is its circuitry or you have a fast blow fuse rather than
a slow blow, which may be needed to avoid blowing during the momemtary
high current to the degauss coil.

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