RCA TV model F27665, CH. CTC203AX shut down problem

[klem kedidelhopper]

This set tries to start four times. HV spikes to 20KV each time and
then decays to zero. I've seen where "three strikes" on some of the
RCA's and the Proscan' s pointed to flyback but I'm not sure I've seen
four. Does anyone have any notes on this one?: Thanks, Lenny

 

[Leonard Caillouet]

"klem kedidelhopper" <captainvideo462009@gmail.com> wrote in message
news:3b059486-c1d6-4436-9d6a-7561c5741ba8@s2g2000yqa.googlegroups.com...

This set tries to start four times. HV spikes to 20KV each time and
then decays to zero. I've seen where "three strikes" on some of the
RCA's and the Proscan' s pointed to flyback but I'm not sure I've seen
four. Does anyone have any notes on this one?: Thanks, Lenny

If you suspect the flyback, look at the collector pulse with your scope.

Leonard

 

[klem kedidelhopper]

On Apr 28, 8:40 pm, "Leonard Caillouet" <no...@nohow.not> wrote:

"klem kedidelhopper" <captainvideo462...@gmail.com> wrote in message

news:3b059486-c1d6-4436-9d6a-7561c5741ba8@s2g2000yqa.googlegroups.com...

This set tries to start four times. HV spikes to 20KV each time and
then decays to zero. I've seen where "three strikes" on some of the
RCA's and the Proscan' s pointed to flyback but I'm not sure I've seen
four. Does anyone have any notes on this one?: Thanks, Lenny

If you suspect the flyback, look at the collector pulse with your scope.

Leonard

I found a few things after I wrote to you. There were two overheated
resistors in the vertical circuit. So I thought that I had found the
area of concern. One of these resistors is in one of the 14V supplies.
There is a diode off the flyback, a cap to ground and one of the two
resistors mentioned above, this 300 ohm resistor which goes to ground.
I would have betted on the diode being shorted but it was good. I
checked around the chip and off the flyback and while no supply line
was dead shorted or apparently severely loaded everything looked ok.
The overheated resistors were good as well.
Then I scoped the hor output collector and found that the pulse was
clean and exceeded 800Vpp. I was able to view it by using the vertical
var. control and it could have been 1100 V or so. John from Del's TV
suggested that I look at the regulator on the stand up AV board. Its
a three terminal plastic case on a small heat sink on the upper part
of the board facing the CRT. I wiggled it slightly while looking for
ring cracks and didn't see any. I then tried the set again just for
the heck of it. Amazingly it came on for five seconds and then shut
off. I repeated this another three times and thinking about the last
thing I touched I re soldered the regulator. I then tried the set
again and it stayed on. I've repeated this now about five times from a
cold start and the set seems to consistently come on. So I think the
shutdown problem could have been related to that regulator. I really
want to put some more time on it and see. The vertical deflection
looks fine also so I don't know what the story is with the two
overheated resistors.
But now there is an additional issue. The set was only showing a
"signal unuseable" message in tuner mode. However if you apply
external video and audio to it it works fine. The puzzling thing about
this is with external AV connected as well as cable, you can switch
between the two and although the upper right side of the screen
toggles between VID and then channel indications, only the AV signal
is displayed continuously. So the set seems to only work on video
input. I went through the menu thinking that perhaps the set needs to
be auto programmed but there isn't an option for that. There is "auto
tuning" but nothing that scans through the channels as previous RCA's
did. I don't suspect the tuner because of the screen toggle issue
although I suppose anything is possible. Are there any other issues
with these that you or anyone else who maybe reading this knows of? Oh
btw I also soldered up the coil on the HOT base circuit. Thanks for
all the help. Lenny