I have a Hitachi TV model #50EX10B. I have replaced the horizontal
output transistor twice. I did just find a faulty transistor in the B+
supply that I think is part of a safety circuit (over voltage). Before
replacing with another HOT, what can I check that would keep blowing
this? All components in the immediate area check good. I have checked
the flyback windings best I could with a DMV, and don't see anything
shorted to ground. The main B+ fuse doesn't blow either. Thanks for any
feedback on this.

Did you use the original HOT 2SC4589-04 ( 2315273 ) ??

kip
wrote in message
ups.com...
I have a Hitachi TV model #50EX10B. I have replaced the horizontal
output transistor twice. I did just find a faulty transistor in the B+
supply that I think is part of a safety circuit (over voltage). Before
replacing with another HOT, what can I check that would keep blowing
this? All components in the immediate area check good. I have checked
the flyback windings best I could with a DMV, and don't see anything
shorted to ground. The main B+ fuse doesn't blow either. Thanks for any
feedback on this.

I have checked the flyback windings best I could with a DMV,

That won't tell you diddly squat. Stick a sine wave up one end of the
windings (remove transformer from set to do it) and poke other end of
winding up a 'scope. The trace should gradually peter out. If the trace
is all squashed up one end then it's shagged.

Yes. I also tried a cross, and it blew also. I did repair several
things in the switching power supply to get the set this far. Now all I
need is high voltage. Just not sure what the most likely component may
be. Thanks for the reply.

I have a sencore LC-101 and did check the primary winding. It tested
good. I'm not sure how to check the secondary though. Don't know what I
should expect. Thanks for the reply. I'll keep digging, and hope to
find something wrong before replacing the HOT.

You might want to check the reparfaq.org site for causes related to failing
HOTs.
Components that I routinely check when I encounter a failed HOT, are all of
the components associated with the base signal of the HOT.

Be sure to review the safety precautions included in the repair site.

The Sencore LC analyzers are good for troubleshooting non-powered board
components.
You can check caps in-circuit for value and ESR. When you encounter readings
that that look suspicious, remove the cap from the board and retest.
The coax and mini-hook clips can be cumbersome for foil-side board ESR
testing, but you can substitute that cable with ordinary test leads plugged
into a BNC-to-bananna adapter attached to the LC input connector. Check
and/or adjust for zero ohms with tips shorted before you begin ESR testing.

If you can determine the pinout of the flyback/IHVT, you might be able to do
a simple check of the HV multipler section with your LC analyzer. The HV
rectifiers need a higher voltage to conduct, higher than that of the more
commonly encountered LV diodes.
The LC analyzer can also perform a basic check for winding-to-winding
leakage if you know the pinout.

The Sencore Video Analyzer units have a Horizontal Drive output for checking
the HV multiplier of flyback/IHVTs.
There are other test methods suggested in the Repairfaq.org contents.

Cheers
WB
..............

wrote in message
ups.com...
I have a Hitachi TV model #50EX10B. I have replaced the horizontal
output transistor twice. I did just find a faulty transistor in the B+
supply that I think is part of a safety circuit (over voltage). Before
replacing with another HOT, what can I check that would keep blowing
this? All components in the immediate area check good. I have checked
the flyback windings best I could with a DMV, and don't see anything
shorted to ground. The main B+ fuse doesn't blow either. Thanks for any
feedback on this.





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