CTC169AS Chassis shuts down after a few seconds

B

BobD

Guest
Hi,
This chassis is in a 31GT656 GE TV. Upon power up, the screen has a
horizontal line made up of seperate RGB lines. After 3 seconds, the
relay clicks and the set comes up with a full bright screen with white
retrace lines. After about 3 more seconds, the set shuts down and
requires a wait before restarting. The CRT voltages seem to check
out(G1=5.0v, Cath=225v). If I power up with a Variac and keep the
voltage around 80%, the set will stay on. I checked the resistance of
the heater to the other pins on the yoke. All except G1 are infinite.
I get about 1.2 ohms to G1 from the heater (with the CRT PCB
disconnected). If I disconnect the heater, the power supply will stay
on (with the CRT PCB connected). I can power the heater from a remote
supply to verify it works, but with the set supply connected, the
heater filaments appear dim. My heater voltage, measured with a DMM,
is around 2.2 volts loaded, 8.5 volts unloaded (heater disconnected).
Bad tube? Any ideas?
Thanks.
 
---------------------------------------------------------------
Text pasted from WinSTIPS 2.0
http://www.ServiceSoftware.com
---------------------------------------------------------------

RCA CTC169

Bright Pix W/Retrace. Audio Ok. Shuts Off In 10 Sec

Bob'S Tv

Q2906 (Q906) Ecg 159 Ok

---------------------------------------------------------------



--
==========================
Jeff Stielau
Shoreline Electronics Repair
344 East Main Street
Clinton,CT 06413
860-399-1861
860-664-3535 (fax)
jstielau@snet.net
========================
"If you push something hard enough it will fall over."
Fudd's First Law of Opposition - Sir Sidney Fudd


"BobD" <rdanek@mail.com> wrote in message
news:d5ace3e5.0311121946.39f5debd@posting.google.com...
Hi,
This chassis is in a 31GT656 GE TV. Upon power up, the screen has a
horizontal line made up of seperate RGB lines. After 3 seconds, the
relay clicks and the set comes up with a full bright screen with white
retrace lines. After about 3 more seconds, the set shuts down and
requires a wait before restarting. The CRT voltages seem to check
out(G1=5.0v, Cath=225v). If I power up with a Variac and keep the
voltage around 80%, the set will stay on. I checked the resistance of
the heater to the other pins on the yoke. All except G1 are infinite.
I get about 1.2 ohms to G1 from the heater (with the CRT PCB
disconnected). If I disconnect the heater, the power supply will stay
on (with the CRT PCB connected). I can power the heater from a remote
supply to verify it works, but with the set supply connected, the
heater filaments appear dim. My heater voltage, measured with a DMM,
is around 2.2 volts loaded, 8.5 volts unloaded (heater disconnected).
Bad tube? Any ideas?
Thanks.
Click to expand...
 
Verify all SMPS power supply voltages first, both in standby and run.
Especially ESR the capacitors and check the 12v supply diode.

A borderline 12v line will cause all kinds of problems.

Seems like you are starting at the wrong end of the tv set for
troubleshooting of a shutdown problem. You have to verify power supply
first, then the deflection/high voltage circuits, then follow the remaining
shutdown causes.

David

BobD <rdanek@mail.com> wrote in message
news:d5ace3e5.0311121946.39f5debd@posting.google.com...
Hi,
This chassis is in a 31GT656 GE TV. Upon power up, the screen has a
horizontal line made up of seperate RGB lines. After 3 seconds, the
relay clicks and the set comes up with a full bright screen with white
retrace lines. After about 3 more seconds, the set shuts down and
requires a wait before restarting. The CRT voltages seem to check
out(G1=5.0v, Cath=225v). If I power up with a Variac and keep the
voltage around 80%, the set will stay on. I checked the resistance of
the heater to the other pins on the yoke. All except G1 are infinite.
I get about 1.2 ohms to G1 from the heater (with the CRT PCB
disconnected). If I disconnect the heater, the power supply will stay
on (with the CRT PCB connected). I can power the heater from a remote
supply to verify it works, but with the set supply connected, the
heater filaments appear dim. My heater voltage, measured with a DMM,
is around 2.2 volts loaded, 8.5 volts unloaded (heater disconnected).
Bad tube? Any ideas?
Thanks.
Click to expand...
 
Once the power supplies are all verified. Bright screen with retrace
indicates a problem in the video output stage or sweep derived power supply
voltages causing the shutdown condition.

I would bet if you have bright screen with retrace, the crt voltages do not
check out as you indicated. Normal G1 low voltage, 20v or so or zero;
Cathodes, 200v with no video at all, lower with some video, never below 125
volts dc even with very bright video unless a problem; G2 can be anywhere
between 200 and 600 volts depending on tube and design.

I would look for low video output power supply voltage, 200v. or a problem
with the luma buffer transistor Q2906 being shorted. Q2906 often shorts due
to intermittent arc-back shorts in the picture tube. Repeated failure of
this transistor after replacing with an EXACT part generally indicates an
intermittent tube problem.

David

David <dkuhajda@locl.net.spam> wrote in message
news:3fb33a30@news.greennet.net...
Verify all SMPS power supply voltages first, both in standby and run.
Especially ESR the capacitors and check the 12v supply diode.

A borderline 12v line will cause all kinds of problems.

Seems like you are starting at the wrong end of the tv set for
troubleshooting of a shutdown problem. You have to verify power supply
first, then the deflection/high voltage circuits, then follow the
remaining
shutdown causes.

David

BobD <rdanek@mail.com> wrote in message
news:d5ace3e5.0311121946.39f5debd@posting.google.com...
Hi,
This chassis is in a 31GT656 GE TV. Upon power up, the screen has a
horizontal line made up of seperate RGB lines. After 3 seconds, the
relay clicks and the set comes up with a full bright screen with white
retrace lines. After about 3 more seconds, the set shuts down and
requires a wait before restarting. The CRT voltages seem to check
out(G1=5.0v, Cath=225v). If I power up with a Variac and keep the
voltage around 80%, the set will stay on. I checked the resistance of
the heater to the other pins on the yoke. All except G1 are infinite.
I get about 1.2 ohms to G1 from the heater (with the CRT PCB
disconnected). If I disconnect the heater, the power supply will stay
on (with the CRT PCB connected). I can power the heater from a remote
supply to verify it works, but with the set supply connected, the
heater filaments appear dim. My heater voltage, measured with a DMM,
is around 2.2 volts loaded, 8.5 volts unloaded (heater disconnected).
Bad tube? Any ideas?
Thanks.
Click to expand...
 
You guys are good! The Q906 transistor is shorted. I will replace and
reply once the new one is in.

Thanks again.
 
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