[TechAssist] Re: CTC197 CRT filaments not ON
- From: mebonnell@xxxxxxxxx (Max Bonnell)
- To: techassist@xxxxxxxxxxxxx
- Date: Mon, 14 Jun 2004 13:20:09 -0500
Joe what does pin 10 of the CRT measure.
If it is low check R15107 (2.2 ohs - 3 watt) going to pin 10.
Max Bonnell
Bonnell TV
Robinson, IL
Sender: repair-bounce@xxxxxxxxxxxxxxx From:
jbc@xxxxxxxxxxxxxx(Joe=A0Batchelor) Date: Sun, Jun 13, 2004, 4:12pm To:
repair@xxxxxxxxxxxxxxx Subject: [TechAssist-B] Re: CTC197 CRT filaments
not ON Reply=A0to: repair@xxxxxxxxxxxxxxx
This is not a normal problem. I have been around a long time but have
never seen anything like this.
With a normal RF signal the filament voltage is so low that the CRT will
not light up. I opened the filament line and fed an external power
supply to the CRT filament and got a picture.
I connected the filament back normal and read with a scope. The voltage
was very low. I noticed that if I had the Sencore feeding an RF signal
to the set the filament voltage on the scope would be good and I would
get a picture.
If I removed the Sencore signal the filament voltage read on the scope
would instantly drop. Put the Sencore back and normal filament voltage.
The Sencore must be putting out a different sync or blanking pulse.
I have not seen it in this chassis but in some older sets problems could
result from an incorrect sandcastle signal.
I ran out of time and have not checked regulation or high voltage.
I was not sure if the filament was coming from the flyback but thanks to
Max Bonnell I now know that it does.
The high voltage must be changing since it is tied to the same source as
the filament.
Horizontal drive signal does not normally change the high voltage, but
this has to be related to the signal, perhaps in the pincushion circuit.
It is sets like that this that makes me want to stay in bed on Monday
morning.
Thanks to all that responded to this problem.
Joe Batchelor CET TX-80
6/12/04 10:43:59 AM, "John at Main TV" <maintv2004@xxxxxxxxxxx> wrote:
It is normal for the screen of a CTC197 to go to a flat grey when no
signal is applied. This may appear black if youur brightness or screen
is set low. Perhaps your antenna signal is weaker than your Sencore RF
signal letting it go grey or it may be related to the video switching
problems. It would be hard to imagine the filament votage changing
unless the series resistors already mentioned are bad or have bad
connections. BTW, the B+ to the horiz. stage should be +141 measured at
cathode of CR14106. The CTC197 in known for bad IHVTs but that usually
results in a dead set. Your problem may be all in the video switching.
This is done in U26901. You will need a schematic to troubleshoot that.
=A0 John.
John Mielke
Main TV
636 main St.
Longmont, Co
phone 303 776 6955
fax 303 776 0792
maintv2004@xxxxxxxxxxx
----- Original Message -----
From: "Joe Batchelor" <jbc@xxxxxxxxxxxxxx>
To: <repair@xxxxxxxxxxxxxxx>
Sent: Friday, June 11, 2004 11:18 PM
Subject: [TechAssist-B] CTC197 CRT filaments not ON
I have a CTC197 that the filament voltage is running too low and the CRT
will not light up. If I feed the Sencore RF signal, the voltage
increases and I get a picture. As soon as I remove the Sencore the
filament voltage drops. That is with no signal and with an anteanna
signal.
I do not have the service data and am trying to use a CTC195 that is for
a big screen. It is hard to trace the filament line. I assume it comes
from the
flyback, but it would
be hard to get reduced voltage unless the pincushion circuit has a
problem.
I think one tip said adjust the size with the service mode, but that has
no effect on
this set.
There is also a problem with the video switch, which allows video in and
RF signal at
the same time. This may or may not be related.
Thanks in advance
Joe Batchelor CET TX-80
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