Question about Panasonic CT25G7 25" TV

1 Answer

No vertical deflection, only a thin horizontal line.

I would appreciate any help I can get for the following problem:
My television set is a Panasonic CTN 2766S and chassis APEDP204.

Problem: The top of the picture was a couple of inches short when the tv was first turned on. After five minutes or so, the picture filled out to normal and stayed that way.

It did this for about a year and then when the set was turned on, it only had a horizontal line in about the middle of the screen. It did not fill out no matter how long it was on.

I replaced the IC 451(LA7836-TV) “VERT OUT” and, also, replaced C553, 22UF/250V with a 32UF/250V capacitor because a service bulletin said the capacitor was drying out. That caused an increase in beam current resulting in a broken CRT neck. 

When the tv was turned on. The raster filled out except for the top couple of inches. Adjusting the vertical size pot did not have any effect. IC 451 was getting hot in a short time. After 30 minutes the raster did not fill out, like it had done previously. I heard a sound like something was shorting out and the raster disappeared leaving only a horizontal line on the screen.

I made a check of IC 451 and found it was shorted.

Again, I would appreciate any help with this problem.

Wally

dede27@norwaymi.com


Posted by on

  • dede27 Feb 24, 2009

    Hi Benimur,



    I also want to thank you for your help, I appreciate it very much!



    I am assuming you have read my response to Shuttle as to why it took me so long to respond.



    I like the very helpful information you sent and I will certainly follow your advice when time permits me to do so.



    You are correct, for the most part, in the wiring of the componets !



    I had mentioned in my reply to Shuttle, I had been told I should have installed a LA 7836 kit. That it not only had the IC but also the resistors, capacitors and othe associated parts. Would you please the me what those parts are and values ?



    Again, I thank you very much for your help!



    Dede

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  • Master
  • 6,966 Answers

Hi and welcome to FixYa,

A few ideas you may want to consider/explore;

  • While it is true that capacitors do dry out, the values that you posted (22uF & 32uF) are relatively low for the pump/boost capacitor which is responsible for the "top of the picture was a couple of inches short". Normally this should be around 100uF connected between pin8 & pin 12 of LA7836;
  • agree that the Vertical IC LA7836 is busted hence the single line;
  • in most vertical designs, there would be a diode from pin7 that goes to pin12 that needs looking into for a leak;
  • pin7 is the Vert B+ ~ 24VDC while pin1 is secondary B+ 9 ~ 12 VDC. In some designs to accomplish this, there is a dropping resistor from pin 7 to pin 1 and sometimes a zener diode from pin1 to GND parallel with a filter capacitor;
  • pin11 is the vertical output that goes to the yoke. From the yoke some design uses another capacitor (about 1000uF) before going to the ground through a low resistor (~ 1 ohm);
  • above mentioned parts need to be checked out of ciruit preferable and special attention to possible leaks of the diode when testing in reverse bias mode.
Good luck and thank you for using FixYa.

Posted on Jan 30, 2009

2 Suggested Answers

Shuttle83
  • 1139 Answers

SOURCE: No vertical deflection,only a thin horizontal line.

Hello dede27,

I suspect you have some background in electronics so I'll ask you some questions.

First, I know that you changed the output ic and a capacitor, the capacitor caused excessive beam current, that's bad, remember that beam current is dangerous because it can produce X-Rays. Remember to use the exact value of parts for X-Ray generating areas of the TV. So replace the C555 with the rated value by the manufacture.

As far as the vertical deflection problem it sounds like you may have a shorted vertical deflection coil (part of the yoke transformer). I would suggest testing the coil to see if it is shorted (A ring test will determine this). The Sencore LC102 has a ring test feature or you can lookup how to build a simple ring tester. In any event replace the IC and test the yoke transformer for shorts on the vertical winding.

I hope this helps,

Thank you,

Shuttle83

http://www.electron-age-technologies-llc.com

Posted on Jan 30, 2009

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Posted on Jan 02, 2017

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Hello dede27,

I suspect you have some background in electronics so I'll ask you some questions.

First, I know that you changed the output ic and a capacitor, the capacitor caused excessive beam current, that's bad, remember that beam current is dangerous because it can produce X-Rays. Remember to use the exact value of parts for X-Ray generating areas of the TV. So replace the C555 with the rated value by the manufacture.

As far as the vertical deflection problem it sounds like you may have a shorted vertical deflection coil (part of the yoke transformer). I would suggest testing the coil to see if it is shorted (A ring test will determine this). The Sencore LC102 has a ring test feature or you can lookup how to build a simple ring tester. In any event replace the IC and test the yoke transformer for shorts on the vertical winding.

I hope this helps,

Thank you,

Shuttle83

http://www.electron-age-technologies-llc.com

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