CTC187 dead

[Mike Bates]

I got this set, friend wants it fixed.

He said the power button is messed up, and it doesnt turn on. well, I seen
that it was a ctc187, I know thats not the case. I got the set, and pressed
the button, it presses fine. I immidiately thought in my head, since I
worked on these before, the 10uf cap in the SMPS primary is gone, fuse is
gone, and STK is wasted. thats what I first thought.


I took it apart, only to confirm my suspician, the fuse is wasted.


I pulled it out, here is the rundown so far: caps look normal, no bloated or
exploaded caps like on most of the ones I worked on.

The fuse is gone, the HOT is shorted, and 1 of the 2 secondary diodes is
shorted. The one that feeds the flyback and associated circuits is shorted.

Ok, question. What caused the HOT to blow in the first place? flyback
possibly bad?

I got another board identical to it, that had a bad STK, and all the power
supply caps. Everything was recapped, but the woman said she tossed it, and
didnt want it fixed, so I never got the STK, and ended up robbing the caps
and the NTSC processor for another set. The HOT and associated circuits are
still OK.

I wonder if I should just pull the flyback and HOT, with the diodes, and
some blue pincussion caps and change them out?

any thoughts would be appriciated.

 

[[email protected]]

Simple ring the flyback to find out if it is bad.
Check the horizontal driver transformer solder connections, could also
short HOT.
Tuner ground problems or corrupted eeprom due to same can also blow
HOT.
Arcing back crt could also cause failure.
Failure in the smps main b+ diode can blow the HOT.

Lots of different possibilities, start doing the basic troubleshooting
for that type of failure, then continue troubleshooting once unit can
be powered up with the main b+ current limited.

David

 

[Vince]

Make sure the diode that supplies the HOTr is good or bad, if its good the
HOTr is bad , you have to unsolder one or the other, either one could cause
the fuse to go.
Vince

 

[Vince]

Hi!
I have found that i can be either the diode that fernishes the power to the
HOTr or the HOTr.unsolder to check, either one of these or the regulator can
take out the fuse.
Vince

 

[Mike Bates]

the HOT is fine, I snipped the diode, and its indeed bad, and that means the
STK is bad, and the 10uf cap in the primary caused it.

Hi!
I have found that i can be either the diode that fernishes the power to the
HOTr or the HOTr.unsolder to check, either one of these or the regulator can
take out the fuse.
Vince