What would cause horizontal "retrace" lines?

[[email protected]]

I am tracking down a possible short in my CRT on an Emerson 27"
MS2700RDA tv.

I have narrowed it down to a possible short between the Red cathode
and the screen grid (G1).

However, during testing the, i.e. isolating heater, switching cathode
connections, removing cathod connections, the horizontal retrace lines
were always visible.

Could there possibly be another reason for the retrace lines beyond
the possible CRT short? Anything in the circuitry feeding the CRT
which would cause this like a bac cap or transistor?


Any suggestions appreciated..

Thanks.

 

[Jerry G.]

It is possible that there is a blanking problem in the set, depending on the
exact nature of the fault.

The most common problem is that there is a short in the CRT. It may not
necessarily be a heater to cathode short. It can be a carbon or particle
build-up somewhere between one of the elements that is causing some
overbias. If the retrace lines are on one colour channel, it is most likely
the CRT that is toasted.

--

Greetings,

Jerry Greenberg GLG Technologies GLG
=========================================
WebPage http://www.zoom-one.com
Electronics http://www.zoom-one.com/electron.htm
=========================================


I am tracking down a possible short in my CRT on an Emerson 27"
MS2700RDA tv.

I have narrowed it down to a possible short between the Red cathode
and the screen grid (G1).

However, during testing the, i.e. isolating heater, switching cathode
connections, removing cathod connections, the horizontal retrace lines
were always visible.

Could there possibly be another reason for the retrace lines beyond
the possible CRT short? Anything in the circuitry feeding the CRT
which would cause this like a bac cap or transistor?


Any suggestions appreciated..

Thanks.

 

[Rock Braud]

Jerry, thanks for the input.

I agree with you and am currently working toward "shooting" the CRT to
clear a possible Red Cathode to Screen Grid (G1?) short. I have a 47
uF 300V cap I plan to use to zap it.

I plan to charge the CAP from a source within the TV, then shut it
down and remove the CRT connector. Then short the Screen Grid (G1?) to
ground and then connect the cap across ground and the Red Cathode.
Then if this doesn't improve the situation I will repeat it for the
other colors.

Do you see any problems with this? Any hints or tips??

Someone mentioned to "shoot" the tube while the CRT is connected and
the TV warmed up. Not sure I am confident enough to try that just yet.

Thanks.

 

[Mr TUBEAMPS]

try replaceing the electro cap that filters
the collecters of each video transistor and check
heater volts if the heaters are dc check the electro
cap that filters them.

john