Panasonic TH50PX60U Power Problem

[teg33]

This 7 year old plasma flat screen has an intermittent power-up problem. Sometimes works fines, sometimes will not power on with either remote or the power button. No blinking lights, nothing.

The TV was not working today so decided to troubleshoot. I followed the "no power troubleshooting chart" in the panasonic training guides found http://www.tgohome.com/ServiceManual...&Search=Submit.

1) can NOT hear the click of the relays after TV plugged in (BTW, when the set does work I DO hear the click of the relays after plugging in)
2) 5V at pin 1 of connector PA40 on the PA board was fine
3) 2.5V at pin 13 of connector P25 on the P board was not there. Meter showed 0V.

The guide says to replace the DG board. Is it really that simple? Can I trust this guide? I would appreciate some insight from others who have used the guides.

Also, any suggestions on how to look-up the proper DG Board part number would be appreciated. It appears that I need the TNPA3903BCS.

Thx

[tom66]

Re: Panasonic TH50PX60U Power Problem

The DG board has the main processor on it -- I believe it controls the standby voltage. There's not prerequisite other than the main processor working. So it would seem the flowchart is correct.

Boards: TNPA3903 is critical, then you must match suffix where possible, unless vendor can confirm that board is compatible.

[teg33]

Re: Panasonic TH50PX60U Power Problem

Thanks for the response! From what I've read there are several standby voltages generated and running through various boards. I think the one I am checking for is generated by the DG board so the guide makes sense.

This morning I plugged in power and heard the relay clicks. Immediately checked for the 2.5V at pin 13 of connector P25 on the P board and it was THERE! In that case, the guide says it's the P board. I pushed the power button and everything went dead, but I'm thinking maybe I didn't wait long enough for everything to initialize?? Does this sound like a P board issue?

Also, I am able to see the top edge of the DG board and see suffix BC, but what does the S mean in TNPA3903BCS?

Thanks again for any responses.

[teg33]

Re: Panasonic TH50PX60U Power Problem

So I have some more information (and questions of course). FYI, i am using this guide http://www.toms-service-manuals.com/...&mfg=Panasonic

I got the relays to click again when I plugged in power cord. Following the flowchart on page 49 I measured 2.7V at pin 13 of connector P25 on the P board. I waited about 15 seconds and heard clicks again. The voltage was gone. Is this signal something that should be constant, or does it only last a short time? The flowchart says nothing about a timing issue.

The reason I am wondering is that page 19 item 3 talks about an F-STB-ON command that is generated from the DG board that only lasts about 15 seconds. That command generates the F-STB-14V signal which I think may be related to the pin I am measuring???

Thanks again for any help!

[tom66]

Re: Panasonic TH50PX60U Power Problem

I know that all 2006~2008 Panasonic plasmas do a self-check when plugged in.

As soon as power is plugged in, two relay clicks are heard. The 15V power supply comes up, and the main board is powered. The set draws around 17~20W in this mode. (Not Energy Star compliant!) After around 20~30 seconds, the set turns off the 15V supply (accompanied by a click of a relay), and power consumption drops to 0.2W or so. It then remains in this mode until unplugged or turned on.

If an error is detected in this self test generally you'll get a 4 or 10 blink error if it's PSU, and a 1, 3, 5, 9 or 10 blink error if it's main board. Note that 10 blink can be either PSU or main board. However, since you are not getting any blink errors, it indicates the self test has successfully passed.

[teg33]

Re: Panasonic TH50PX60U Power Problem

On the few occassions where I hear the relays click when power is applied, I think something is dying before it ever gets through self-test. It used to be whenever I heard those clicks the TV would work fine, but now it seems that everything stops and the power button never works.

I just realized the flowchart takes a different path when the initial clicks are heard. The next step is to listen for relays when attempting to turn power on. Since everything appears dead there are no clicks, so it suggests measuring for 3.3V at pin 1 of connector HC01 on the HC board. There is 0V at this point so again says replace DG Board.

Even though the TV is intermittent, I guess both flowchart paths are suggesting the DG so probably should replace it. Does that sound reasonable based on these symptoms? Is this a common board to fail in the Panasonic sets?

Thx

[tom66]

Re: Panasonic TH50PX60U Power Problem

Do you hear two clicks, or three, within the first few seconds?

[teg33]

Re: Panasonic TH50PX60U Power Problem

When I get them (and it doesn't happen every time) I hear 2 clicks. After a couple seconds a red LED lights on the DT board. Then things get variable:
- after about 18 seconds there is a click and the red LED goes out, I think this might be normal operation but when I press the power button I sometimes hear a relay click and sometimes do not
- sometimes there is a click before the 18 seconds and the red LED goes out, no response from the power buttom after that
- sometimes after the 18 second timeout, if I let it sit it will click twice and appears to start over, sometimes if I let it sit it will do nothing.

Does this help?

Basically, per the troubleshooting chart I have seen 3 different paths as shown in the attached image. If I believe this it tells me to replace both the P and DG boards.

Is there anything specific I should check on either of these boards? The DG board is buried but the P board is easy to check?

Thx again for any replies!

[teg33]

Re: Panasonic TH50PX60U Power Problem

Update to my earlier post with another scenario...

- 2 clicks when applied power, 18 seconds later 1 click and red LED went out, about 15 seconds later pushed power button and everything started over with 2 clicks except when I pushed the power button this time nothing.

It certainly appears that either the P or DG board has a failure and is somehow influencing the other board. Should I just replace them both? Or perhaps try one at a time but which one first? If one of these is bad can it damage the other one, i.e. any chance I fry a new board by changing only one?

I'd really appreciate some guidance from someone with experience in these repairs.

Thx

[tom66]

Re: Panasonic TH50PX60U Power Problem

If the first test passes, you probably have a DG board issue.

[teg33]

Re: Panasonic TH50PX60U Power Problem

Thanks for the reply, but I am not following. Which first test are you referring too?

[teg33]

Re: Panasonic TH50PX60U Power Problem

Also on my other question, do you think a bad P board could have damaged the DG board? I would hate to put in a new DG board and damage that one too.

[tom66]

Re: Panasonic TH50PX60U Power Problem

The first test is the two relays clicking, followed by the delay and the final click. If the delay is around 15 to 25 seconds, the DG board has not detected any fault from the P board's outputs.

The P board would not usually be able to damage the DG board due to the overvoltage protection provided in the form of 4 blinks.

[teg33]

Re: Panasonic TH50PX60U Power Problem

Okay, but that first test doesn't always pass. The thing that bothers me is sometimes I get a sequence that indicates the P board is bad (2 clicks, delay, 1 click but then no response when pushing power button). Could the DG board cause that to happen?

[tom66]

Re: Panasonic TH50PX60U Power Problem

When the relays click, measure the 15V output of the PSU. Is this OK?

[teg33]

Re: Panasonic TH50PX60U Power Problem

Thanks for the suggestion. I have no wiring lists, do you know where I can find the 15V output to measure?

[tom66]

Re: Panasonic TH50PX60U Power Problem

Isn't there a point in the flowchart for it?

[teg33]

Re: Panasonic TH50PX60U Power Problem

It wasn't in the flow chart but I looked back through the training manual and found 15V pinout information on page 49. I will check it when I get home tonight, assuming I can get the relays to click when I apply power

Thx again!

[teg33]

Re: Panasonic TH50PX60U Power Problem

I looked for 15V on P board connector P12 pin 4. Two scenarios:
1) First time I plugged in power cord, 2 clicks, delay, 1 click, pushed power button, nothing happened, never saw 15V the whole time.
2) Had to plug/unplug power cord several times to get 2 clicks again, delay, 1 click, pushed power button and TV powered up as normal. I measured 15V only when it powered up.

What do you suggest as my next step?

I was wondering, isn't this kind of intermittent operation the classic bad cap scenario? Maybe I should be checking a few specific caps if someone knows where to look?

Thx again!

[tom66]

Re: Panasonic TH50PX60U Power Problem

I'm not sure what to make about the intermittent 15V!

Is there an F 15V STBY ON signal anywhere?