The problem is vertical section of the panasonic colour television model no-TC-20L3T.please tell me the value of the protection diode [d-449]the colour code is adopt in this diode ,first colour is orange then blue.
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If you wish to get some details; check the site linked here. Pull up older posts. http://electronicshelponline.blogspot.com/
Circuit diagrams of many popular brand TVs and other devices are given.
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Sounds like you've had a failure of a part in the electronics. Plasma TVs use pretty high voltages (like the old picture-tube models) and parts can get fried over time. You'll need to have your Panasonic serviced by a qualified technician. Don't try to do it yourself -- high voltages, remember?
First, You should to replace by original part, then you should check the voltages on power supply, and check the voltage for vertical IC based on datasheet, also check the voltages on vertical section including yoke and last you should check the ESR capacitors on vertical section.
Vertical scan output section circuit fault. Horizontal line problem. If you wish to get some details; check the site linked here. Viewing it in "Mosaic" or "Magazine" will make surf easy Pull up older posts. Surf the site with patience. http://electronicshelponline.blogspot.com/
Your TVs vertical output Ic may be damaged. You just open your TV and locate the vertical section inside, usually panasonic uses Ic numbered [LA7837] which will be marked as part number IC451 on the circuit board. It is a 13 pin Ic, sometimes the number may be different in your TV, as Panasonic uses four types of LA series Ics in their sets. I think that you have some knowledge in the service field, so the complaint states only "loss of vertical sweep", and so I'm not going too deep into description. OK.
Shrinking picture is a voltage regulation problem in the switch mode power supply, Possibly a cap used in the feedback circuit. Or an over current condition on the B+. This is a very tech intense repair because there is no magic bullet. If it is shrinking on bright scenes then you can bet it is a regulation problem, bright scenes draw more current from the power supply causing this effect. I would not suspect the horiz output because the regulation for this circuit usually comes from the main switch mode power supply. One diagnostic is to monitor the B+ going to the horizontal output and see if it fluctuates. If so you can bet it is a cap or optical coupler in the switch mode circuit.
See page 8 of the manual at:
The bracket shown there looks like the mounting holes (4?) are vertical on the back of the TV. They may be identified by an arrow pointing to them. There will be two holes on each side of the TV centerline to attach the vertical components of the bracket that hang on the horizontal angle bars on the wall.
My experiance is to not put money into a TV that is over ten years
old. TVs stress out their electronic components worse than almost
any other electronic product. After 10 years, there are so many
parts that are ready to fail that your are probably wasting your money
trying to get any more life out of it.
Another option is to wholesale replace the main board by sending it to
Module Exchange at 972-298-1212, or PTS Electronics
Be careful on buying a new one though. Often times, these new
technology ones are much worse. Always Google the model number of
the set you intend to buy and add the word 'repair' or 'complaint' to
see if it is one of the many models that are customer service
nightmares being produced by even the most reputable companies today.
Hope ya fix it!
Without looking at the set I would think the problem was in the optic block. An expensive repair, but, since the set is only four months old it's under warranty.
Go to the service section of Panasonic.com and find an Authorized Service Center (ASC) in your area to have the set repaired.