Panasonic TV Vertical Deflection


  #1  
Old 03-25-03, 05:01 PM
ravi
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Question Panasonic TV Vertical Deflection

Hi,
I have an old Panasonic TV, which is almost 10 years old with the model #PC-29XF20A.

Every time I turn "ON" the TV, there is a vertical foldover for about 2" from the top of the screen then slowly goes further down, and some times it comes all the way to ½ size of the
screen. Rest of the picture used to be crystal clear. Now, sometimes bottom portion is also missing couple of inches.

I have read some books such as TV Repair for Beginners and now trying to fix it. I found two leaky resisters in the circuit. Before I replace, I wanted to get the opinion from the experts.

Please share your thoughts. Give me some directions. If I have to remove the circuit board from the TV. I will have to remove the Cathode tube which goes to the flyback transformer. Is it OK to do it. Should I discharge the voltage? It's is not used for last three days.

I don't have a schematic for this unit. Where can I get it?

I am thanking you in advance for your assistance.
Thanks, Ravi
 
  #2  
Old 03-26-03, 10:24 PM
Teratum
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In my 30+ years of repairing various electronic circuits, I have never seen a leaky resistor. Resistor is either short, open or change value, but never leak. Capacitors, diodes and transistors do.

TV, especially Japanese made, is always designed to be repairable easily without removing much of the components. Most components on the circuit board are normally accessible by simple slide the board or tilt the TV set side way, or removing some simple components. I've never had to remove the CRT or flyback to get to other components when I edTV. Something is not quite right here.

From the symptom of your TV, most likely you have leaky capacitors somewhere in your vertical deflection circuit. You got to find it and replace it.

Service manual can be ordered from www.servicemanuals.net.
 
  #3  
Old 03-28-03, 05:46 AM
ravi
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Question Panasonic TV Vertical Deflection

Hi,

Unfortunately, I used the wrong term. I did mean “Transistor” not resistor. It makes more sense. As you mentioned, I can just slide thru the circuit board and work on it.

I was following the TV Repair for Beginners book to troubleshoot the problem. I used the cheapest pocket size tester. When I checked the transistor, for the resistance, I used the leads for emitter and collector. There were only two of the transistors found to be leaky (or open). I hope these two for vertical deflection. The part numbers for the transistors are T D1556 2D and M.231 AN7812.

Am I doing the right thing here? Please let me know. Your assistance highly appreciated.

Thanks, Ravi
 
  #4  
Old 03-28-03, 08:44 PM
Teratum
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I think you are doing the right thing here. It makes sense that the vertical transistors are leaky. Transistors are normally inexpensive, replace it and see if it fixes the problem.

I don't think you have to worry about cheap or expensive pocket voltmeter, since the type of work you are doing does not require super accurate measurement. Any voltmeter can do.

One suggestion from my experience that nothing is more frustrate than replacing a suspected component and the problem is still there. Using voltmeter to measure the voltages at B, C and E can give you quite a bit of confidence on the suspected problem.
When you say you have 2 leaky transistors, did you measure them while they still on the board or out of the board? If it's still on the board, can you read me the voltages at B, C and E for both transitors? I can then tell you whether they are normal or abnormal and why.

I wrote in one of the DIY column a while back about using a cheap voltmeter to measure transistors. I will have to check if it is still posted.
 
 

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