ctc187 output runs hot

[techo]

set came in with a blown horizontal output transistor. you could tell
it had been running hot. we replaced with an original rca transistor
(in an original rca bag) all voltages check ok, picture looks great,
but after 15 minutes the heat sink is super hot. this is a 31" model.
removed driver transformer and cleaned the lugs and resoldered.
Still runs hot. replaced the flyback, still runs hot. Anyone have a
suggestion? thanks

 

[John Del]

Subject: ctc187 output runs hot

From: [email protected] (techo)
Date: 10/14/03 4:39 PM Eastern Daylight Time
Message-id: <[email protected]>

set came in with a blown horizontal output transistor. you could tell
it had been running hot. we replaced with an original rca transistor
(in an original rca bag) all voltages check ok, picture looks great,
but after 15 minutes the heat sink is super hot. this is a 31" model.
removed driver transformer and cleaned the lugs and resoldered.
Still runs hot. replaced the flyback, still runs hot. Anyone have a
suggestion? thanks

Check the emitter resistor (smd), then swap out the horiz driver transformer.

John Del
Wolcott, CT

"Nothing is so opportune for tyrants as a people tired of its liberty."
Alan Keyes

(remove S for email reply)

 

[David]

Connections to the hdriver transformer are bad causing distortions on the
drive waveforms. Simply resoldering is NOT good enough. The transformer
needs removed and the pins carefully scraped clean of the contamination.

I would assume you already check things like proper b+ voltages, leaky pin
diodes, noise on the b+ to the flyback etc.

David

 

[techo]

the driver transformer had been removed and lugs cleaned off...still
have the problem. diodes replaced, voltages seem normal. b+ looks
clean

 

[Franc Zabkar]

set came in with a blown horizontal output transistor. you could tell
it had been running hot. we replaced with an original rca transistor
(in an original rca bag) all voltages check ok, picture looks great,
but after 15 minutes the heat sink is super hot. this is a 31" model.
removed driver transformer and cleaned the lugs and resoldered.
Still runs hot. replaced the flyback, still runs hot. Anyone have a
suggestion? thanks

I don't know this set, but I had a similar problem in a monitor which
I traced to an electrolytic cap connected to the "primary" side of the
horizontal drive transformer. Also check that there is no ringing in
the base drive to the HOT, and measure the tuning cap and damper
diode.


- Franc Zabkar

 

[RonKZ650]

You're sure you used the correct part # RCA output? They used a lot of
different ones. Also check the horiz driver transistor itself. I've had a
couple sets recently that seemingly worked fine, but would short the output
after a short time that had a bad driver.
Ron

 

[Jason D.]

Check the emitter resistor (smd), then swap out the horiz driver transformer.

John Del
Wolcott, CT

Claps claps.

Hot damn, this rca set I fixed (CTC187) blew HOT again but luckily
didn't take out more parts. Remembering your comment checked the
emitter resistor and oh wow, IS open (I think R4306 2.4K 1/10W SMD),
did run without that. Fixed it once and all 2 days ago, HOT heatsink
ran cool than usual which is remarkable for me as I was used to see
toasty heatsinks in RCA stuff.

Thanks for saving me from long day on this 187 and helps me to bring
closer to understanding the horizontal stuff.

Yes, I did replace the transformer driver and did every point for good
solder connections, replaced B+ capacitor.

Cheers,

Wizard