Wednesday, May 21, 2014

Panasonic TH-P42X30K Plasma TV Power Board Fix

By leorick  |  5/21/2014 12:08:00 AM 8 comments

This is my own Plasma TV. Symptom, sudden power cut off. Power LED not lit at all when the side power button switched on. According to the service manual [ th_p42x30d_g_k_m_p_s_v_1.pdf ] , this is power board issue.

Trace further and narrow down the search to standby power section. Standby voltage (5V) is totally down.

B159-003 Power Board Block Diagram

This section on the B159-002 power board, component side.

B159-002 Power Board Component Side

This diode fails become short circuit, part of the secondary side of the transformer that feedback to FAN6754 PWM controller pin 2 (FB)

FAN6754 Typical Application schematics, not the actual schematics

It is B3100 diode that should be able to withstand 100V peak and 70V RMS reverse voltage


Replace this FML-G22S, the best I have currently, salvage from old PCB.
It can withstand 200V peak.

Now, I can see the 5V standby voltage. Put everything back together and test.

Will try to find the actual component soon (B3100) for replacement.


Good job fixing the power supply, it is often the problem in modern TV sets, a single cheap component failing in the power supply because it was slightly underdimensioned for the current or voltage.

This is power PCB of th-p42x30d. Can you tell me where the B3100 and FAN675 pwm are located.I am finding it hard time to locate as the service manual does not mention power board schematic in detail or component list of p board.

leorick said...

Your power board is totally different from mine. But what I can guess is, the similar diode (like my B3100 diode) should be located here (refer image below)

Power Board : MPF6907 - N0AE5JK00006

I have added additional pictures near diode D452 see folder near-diode in the above link.

I have earlier diagnosed and found the power board to be defective according to the trouble shooting procedures in the manual. Even a panasonic technician confirmed this when he had a look into it.
I was told that the tv was working ok till about 11pm and was switched off by remote and left in stand-by state overnight and found in the morning the stand-by led was off. No response from remote or by power-on/off cycle. We hear three clicking noise when we switch on the tv that's all.

leorick said...

Trace from the input, P9
before D001 (bridge) 240VAC shoud be there.
after D001 it will become between 300-400VDC
PFC_OUT and PFC_GND should be moreless the same (300-400VDC)
STB_Vin should be half than PFC_OUT against PFC_GND (half bridge)

PROBE WITH CARE, P9 is connected directly to main.

after that, hmmm... quite hard to tell.
What are IC001 and IC101 part no?

try this... verify and check every diodes on the board (for short or open)
you might be able to find the problem.
I usually did it this way when too lazy to trace. :-)

Anonymous said...

Hi There,
I have a THP42X30A with the same symptoms as depicted in your blog. However my part that has let go is a different component. It is on the same foil side of the board U207 just above RJ31.
I am wondering if any one knows the value or has a parts list that they can advise me from.

Thanks Clayton

Zotin K said...

A friend brought a dead Panasonic TH-P42X30T. I suspected the standby supply from the start and sure enough, there's no output from that section. Thanks to you, I was able to quickly isolate the problem. The B3100 diode *is* shorted here too. However, I don't have any power schottky diode with a voltage rating over 45V.
Did you happen to observe the actual peak reverse voltage with a 'scope after you fixed it? As it's a low-voltage supply, I was wondering if I could get away with a 45V diode. The failure could be due to marginal current rating rather than voltage. You're covered both ways with the FML-G225 but I don't have anything comparable.

Brilliant! Thank you so much for sharing this. I installed a replacement B3100 but it didn’t work so put the G22 in and it works again.

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