Hi, can anyone tell me what may cause the base-collector voltage to be
over 1000V?
If the HOT is connected B-C voltage is over 1000V and voltage at base
is less than 1 volt, if i remove the HOT, B-C voltage drops to 112V and
Base still is less than 1V.

Voltage at chopper transistor´s collector (low voltage power supply)is
also over 1000V...
Can anyone tell me what is going on?
What can cause these very high voltages?

Thanks.

onyxx:
The high voltages you are reading with your meter are a result of back emf
as a result of fast switching of the transformer's input power.... that is
why the voltage ratings for Collector to Base and Collector to Emitter
have to be upwards to 1500 volts for these kinds of semiconductors that do
the switching.
You should not be measuring these points with your meter.... damage can
easily result.
Do a little reading a the website for this newsgroup at
http://www.repairfaq.org/
there, with some searching, you will find a wealth of pertinent information
that will answer a lot of your questions as you continue to learn about
electronics servicing.
--
Best Regards,
Daniel Sofie
Electronics Supply & Repair
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"onyxx" wrote in message
oups.com...
Hi, can anyone tell me what may cause the base-collector voltage to be
over 1000V?
If the HOT is connected B-C voltage is over 1000V and voltage at base
is less than 1 volt, if i remove the HOT, B-C voltage drops to 112V and
Base still is less than 1V.

Voltage at chopper transistor´s collector (low voltage power supply)is
also over 1000V...
Can anyone tell me what is going on?
What can cause these very high voltages?

Thanks.

If you use a cheap meter, you will get false readings
due to the 1200 volt P-P AC pulse @ the collector,
when the HOT is conducting. You can damage you
meter, or kill your T.V., if your not careful. Sky.



"onyxx" wrote in message
oups.com...
Hi, can anyone tell me what may cause the base-collector voltage to be
over 1000V?
If the HOT is connected B-C voltage is over 1000V and voltage at base
is less than 1 volt, if i remove the HOT, B-C voltage drops to 112V and
Base still is less than 1V.

Voltage at chopper transistor´s collector (low voltage power supply)is
also over 1000V...
Can anyone tell me what is going on?
What can cause these very high voltages?

Thanks.