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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Old November 22nd 04, 05:45 AM
Bobby Villamor
 
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Default Toshiba high voltage problem

Hello everyone.
I am working on a 27in. toshiba color tv model CF27G50. Original trouble
symptom is that
when I push the power button on, the relay clicks supplying power and I
could hear the high
voltage attempting to build up then just about a second the relay clicks
turning the ac supply off.
I have tried disconnecting each low voltage power loads to check which
circuit or component
causes the relay to turn off almost instantly until I reach the high voltage
section.
When I turn the power button on I see some sparks in the picture tube
electron gun - somewhere
around the filament / cathode area, then the relay turns off.
When I remove the high voltage cap from the picture tube the relay remains
on already, high voltage
is produced but the weird thing is that when I push the power button on the
pcb or attempt to touch
any ground connection: wire, heat sink, etc., a high voltage arc jumps from
the ground to my
finger before my finger touches it and I receive a mild electric shock.
Looks like excessive high voltage? But why do arc jumps even when a ground
terminal is touched?
I tried connecting in parallel the two snubber capacitors - those connected
across h.o.t. with a
capacitor of smaller value but no effect.
I would appreciate any hint, comments or help regarding this problem.
Thank you very much.
Bobby



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Old November 22nd 04, 10:46 AM
Art
 
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Sparks inside the crt are not normal, probably the source of your problem.
"Bobby Villamor" wrote in message
news:[email protected]
Hello everyone.
I am working on a 27in. toshiba color tv model CF27G50. Original trouble
symptom is that
when I push the power button on, the relay clicks supplying power and I
could hear the high
voltage attempting to build up then just about a second the relay clicks
turning the ac supply off.
I have tried disconnecting each low voltage power loads to check which
circuit or component
causes the relay to turn off almost instantly until I reach the high
voltage
section.
When I turn the power button on I see some sparks in the picture tube
electron gun - somewhere
around the filament / cathode area, then the relay turns off.
When I remove the high voltage cap from the picture tube the relay remains
on already, high voltage
is produced but the weird thing is that when I push the power button on
the
pcb or attempt to touch
any ground connection: wire, heat sink, etc., a high voltage arc jumps
from
the ground to my
finger before my finger touches it and I receive a mild electric shock.
Looks like excessive high voltage? But why do arc jumps even when a ground
terminal is touched?
I tried connecting in parallel the two snubber capacitors - those
connected
across h.o.t. with a
capacitor of smaller value but no effect.
I would appreciate any hint, comments or help regarding this problem.
Thank you very much.
Bobby




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Old November 22nd 04, 11:26 AM
Ian Malcolm
 
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Default

Art wrote:

Sparks inside the crt are not normal, probably the source of your problem.
"Bobby Villamor" wrote in message
news:[email protected]

Hello everyone.
I am working on a 27in. toshiba color tv model CF27G50. Original trouble
symptom is that
when I push the power button on, the relay clicks supplying power and I
could hear the high
voltage attempting to build up then just about a second the relay clicks
turning the ac supply off.
I have tried disconnecting each low voltage power loads to check which
circuit or component
causes the relay to turn off almost instantly until I reach the high
voltage
section.
When I turn the power button on I see some sparks in the picture tube
electron gun - somewhere
around the filament / cathode area, then the relay turns off.
When I remove the high voltage cap from the picture tube the relay remains
on already, high voltage
is produced but the weird thing is that when I push the power button on
the
pcb or attempt to touch
any ground connection: wire, heat sink, etc., a high voltage arc jumps
from
the ground to my
finger before my finger touches it and I receive a mild electric shock.
Looks like excessive high voltage? But why do arc jumps even when a ground
terminal is touched?
I tried connecting in parallel the two snubber capacitors - those
connected
across h.o.t. with a
capacitor of smaller value but no effect.
I would appreciate any hint, comments or help regarding this problem.
Thank you very much.
Bobby


Ive seen a few like this. Try removing the tube base board then take a
cler plastic 12" ruler and hook a testlead from the end of the ruler to
the ground strap on the tube. Make sure theat no part of the chassis is
within 6" of the tube pins. Switch on, and holding the ruler by the end
without the wire, bring the wire near then right up to the pins of the
tube neck board. If it starts to arc back away and switch off, the tube
has leaked and is gassey. BER but save the good chassis.

The other common cause of arcing in and around the tube neck is if the
ground pin of the Screen/Focus unit on the side of the LOPT is
disconnected. Symptoms are, tube base board arcs accross spark gaps
even if removed. No arc from tube (may 'fizz' a bit if the EHT is
excessive). Close inspection reveals arcing under LOPT. You may be
able to mend the broken pin, but LOPT replacement is reccomended if you
cant make a good joint onto the remaining pin.

--
Ian Malcolm. London, ENGLAND. (NEWSGROUP REPLY PREFERRED)
ianm[at]the[dash]malcolms[dot]freeserve[dot]co[dot]uk [at][email protected], [dash]=- &
[dot]=.
*Warning* SPAM TRAP set in header, Use email address in sig. if you must.
  #4   Report Post  
Old November 22nd 04, 12:07 PM
Jerry G.
 
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Default

Sparks inside of a CRT means that air has leaked in, and a new CRT is the
only fix. In the case of this model of TV set, it would be time to get a new
one.

--

Jerry G.
======


"Bobby Villamor" wrote in message
news:[email protected]
Hello everyone.
I am working on a 27in. toshiba color tv model CF27G50. Original trouble
symptom is that
when I push the power button on, the relay clicks supplying power and I
could hear the high
voltage attempting to build up then just about a second the relay clicks
turning the ac supply off.
I have tried disconnecting each low voltage power loads to check which
circuit or component
causes the relay to turn off almost instantly until I reach the high
voltage
section.
When I turn the power button on I see some sparks in the picture tube
electron gun - somewhere
around the filament / cathode area, then the relay turns off.
When I remove the high voltage cap from the picture tube the relay remains
on already, high voltage
is produced but the weird thing is that when I push the power button on
the
pcb or attempt to touch
any ground connection: wire, heat sink, etc., a high voltage arc jumps
from
the ground to my
finger before my finger touches it and I receive a mild electric shock.
Looks like excessive high voltage? But why do arc jumps even when a ground
terminal is touched?
I tried connecting in parallel the two snubber capacitors - those
connected
across h.o.t. with a
capacitor of smaller value but no effect.
I would appreciate any hint, comments or help regarding this problem.
Thank you very much.
Bobby




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Old November 22nd 04, 11:40 PM
James Sweet
 
Posts: n/a
Default


"Bobby Villamor" wrote in message
news:[email protected]
Hello everyone.
I am working on a 27in. toshiba color tv model CF27G50. Original trouble
symptom is that
when I push the power button on, the relay clicks supplying power and I
could hear the high
voltage attempting to build up then just about a second the relay clicks
turning the ac supply off.
I have tried disconnecting each low voltage power loads to check which
circuit or component
causes the relay to turn off almost instantly until I reach the high

voltage
section.
When I turn the power button on I see some sparks in the picture tube
electron gun - somewhere
around the filament / cathode area, then the relay turns off.
When I remove the high voltage cap from the picture tube the relay remains
on already, high voltage
is produced but the weird thing is that when I push the power button on

the
pcb or attempt to touch
any ground connection: wire, heat sink, etc., a high voltage arc jumps

from
the ground to my
finger before my finger touches it and I receive a mild electric shock.
Looks like excessive high voltage? But why do arc jumps even when a ground
terminal is touched?
I tried connecting in parallel the two snubber capacitors - those

connected
across h.o.t. with a
capacitor of smaller value but no effect.
I would appreciate any hint, comments or help regarding this problem.
Thank you very much.
Bobby



Usually sparks inside the CRT mean the tube has cracked and needs to be
replaced. Sometimes they crack under the yoke where you can't see it, I had
one I was checkihg out, I went to pull the neck board off and the whole neck
of the tube came off in my hand.




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