RCA CTC169 B+ Problem?

[Sam Pzapht]

I have got a 46" RPTV RCA CTC169 chassis that has the proper B+ voltage in
Stand-By: 143.5V. However, when I turn the TV on the B+ drops to 114V. The
audio is fine and I have OSD but the convergence is not right and I do not
have full vertical or horizontal deflection. Has anyone seen this before
with this chassis? Thank You!

Sam

 

[John Del]

Subject: RCA CTC169 B+ Problem?

From: "Sam Pzapht" [email protected]
Date: 12/27/04 1:37 PM Eastern Standard Time
Message-id: <[email protected]>

I have got a 46" RPTV RCA CTC169 chassis that has the proper B+ voltage in
Stand-By: 143.5V. However, when I turn the TV on the B+ drops to 114V. The
audio is fine and I have OSD but the convergence is not right and I do not
have full vertical or horizontal deflection.

You can unload the sweep section and use a 100 watt light bulb as a load on the
140 volt line. If the voltage is normal, you have a load on the supply. If
the voltage stays low, the power supply is the problem.

Monitor the raw B+ during run; I've run into bad solder on the bridge rect that
will cause a severe sag under load.
John Del
Wolcott, CT

"I'm just trying to get into heaven, I'm not running for Jesus!"
Homer Simpson

(remove S for email reply)

 

[Jason D.]

You can unload the sweep section and use a 100 watt light bulb as a load on the
140 volt line. If the voltage is normal, you have a load on the supply. If
the voltage stays low, the power supply is the problem.

Monitor the raw B+ during run; I've run into bad solder on the bridge rect that
will cause a severe sag under load.
John Del
Wolcott, CT

CTC169 has two regulator feedback circuits. One for standby mode via
this IC (burst mode) and cold side feedback in run mode. You have
problem with run mode feedback circuits, it is made up of few
transistors and few resistors, some has precision resistors, sealed
pot (do not adjust this!) this run feedback monitors the B+ output.

Cheers,

Wizard

 

[Art]

There are at least two, maybe more caps in the regulator circuit that will
affect the B+ level because they affect the operating parameters of the
regulator ic.

 

[Sam Pzapht]

I do not have a schematic on this particular chassis, can anyone tell me
which transisitors and/or resistors I need to look at? Will they be on the
primary side of the chopper transformer or the secondary side? Thanks!

 

[Art]

Probably in the right area, ESR the Electrolytics in the regulator area.
SAMS Photofacts are available.