Wednesday, April 27, 2016

Panasonic TC-P55ST30 7 blinks help and repair SC TNPA5351 and buffers

Just finished uploading a video on troubleshooting Panasonic TC-P55ST30 plasma TV that doesn't want to start and blinking 7 times on the front LED.

It was actually broken up in 3 parts you can find on YouTube:

Troubleshooting Panasonic  TC-P55ST30 part 1:
 

Troubleshooting Panasonic  TC-P55ST30 part 2:

Troubleshooting Panasonic  TC-P55ST30 part 3:

Those are not a complete DIY videos and do not show you how to actually do the replacement and repair parts; they are focused more on diagnosing the problem.

We haven't activated the corresponding repair services and repair kits at the site yet, but chances are by the time you hit this posting we already would have had it done. (is that a proper tense?)

Those should help you find them:

http://www.coppelltvrepair.com/search?q=TC-P55ST30

http://www.coppelltvrepair.com/p/1443/repair-service-for-tnpa5340-txnsu1pauu-su-buffer-board-for-panasonic-tc-p55gt30-tc-p55st30-7-blinks-problem

http://www.coppelltvrepair.com/p/1444/repair-service-for-tnpa5341-txnsd1pauu-sd-buffer-board-for-panasonic-tc-p55gt30-tc-p55st30-causing-7-blinks


Now, I would like to summarize the videos:

1) To troubleshoot a TV you need a multi meter. It doesn't have to be a nice Fluke, a generic $30 device would do 99% of the time.

It is worth spending some time watching YouTube videos on how to measure voltage and resistance with the device.
For sake of finding shorts and generally troubleshooting resistance (or continuity, which is the physically and mathematically opposite of resistance) is usually measured using the DIODE symbol on the device's dial for reasons you can find explained elsewhere.

2) You need to take off the back cover of the TV. Some TVs allow it to be taken while the unit is on its feet/pedestal, others require that the pedestal is taken out and the unit is laid flat.
It is quite OK to lay a plasma TV flat on a table.

3) If you see lots of dust in a TV (or any other device) take it out and suck it or blow it out of it. Doing that earlier is better than doing it later when you've picked and / or inhaled large portions of it.
Do as we say , not as we do in this video :-)

4) Most commonly failing power components in plasma TVs are transistors and diodes.
Transistors have 3 electrically different legs and diodes have 2 even though it is possible for a particular component that is a diode to have 3 legs and look like a transistor; this would be when inside there are 2 diodes with one common electrode or simply two of the legs would be the same electrode.
On boards didodes are often marked with prefix D followed by a number while transistors are often marked with prefix Q followed by a number. D101 is a diode, Q101 is a transistor.

5) You check for defective diodes and transistors by testing each possible combination of electrodes for low resistance near to 0. A true failure would have the same low resistance in both direction, e.g. by swapping the places of the meter's probes you should get the same low reading.
Low reading in only ONE direction is usually indication for a GOOD device.

The separation between diodes and transistors is only important for the sake of knowing that in some cases you will find "shorted" electrodes, that are such by design - namely in diodes made with 3 electrodes.

6) Two things to watch for when looking for shorted components:

First, often times components are in parallel; one shorted component may make others appear shorted as well. Which means the first component you find shorted is not necessarily the actually bad one.

And second, sometimes low resistance can be found between two electrodes of a power component by design; this is fairly common with transistors in particular and easily recognizable once you establish the pattern, which is that such resistances have "rounded" values of say 15 or 20 ohm, which are hard to achieve my a failure (not impossible though!) and, most importantly, can be easily tracked to a resistor located nearby.

7) Not just SMD components fail. Check the ones on the heat sinks as well.

In addition, not only components included in repair kits sold by SJ and others fail. Many times companies sell you repair kits that were not even based on actual experience repairing boards.
Do not trust that if you buy a repair kit from SJ or even CTVR it will have all the parts you need!
But naturally I think it stands to reason to trust companies who offer repair services in addition to repair kits.


8) Transistors are sometimes organized in groups of 2, 3 or more working in parallel (one particular electrode labeled G leg is usually connected to the other G-s via small resistors while the other electrodes are directly electrically connected to the same electrodes from the other components in the group).
Determining which one of those has failed is subject of another article for sake of space, but it is a good idea to replace all of them when one fails.
It is not a must in most cases we've seen, but in some cases it is.
For Panasonic TC-P55ST30 it doesn't seem to be, but we still do it.

9) We've seen different failures on different boards; the video identifies the components we've seen fail.

You can get a repair kit from us or send the board for repair if you wish.

10) When the sustain board fails a buffer board may or may not fail along with it.

When it fails it is usually, but not necessarily the top (SU) buffer board.

The videos show you how to test for failure (short) on a buffer board and how to identify the faulty IC.

The method shown is 99% reliable meaning it leaves about 1% of the times when the board would be bad, but the shown check may not reveal it. The devil is in the details, right?

You can buy the ICs for the buffer board repair or send them to us to have them repaired and tested.

Hope this helps!

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