Panasonic TC-P54VT25 No image. A or D board?

[canadaboy25]

I have a Panasonic TC-P54VT25 that will power on and prime the display but there is no image at all.

The panel is primed as there is a slight glow from the entire panel. This means the problem should be logic related. The service manual also confirms this and recommends replacing the A or the D board.

I have tried to get the TV to display the test sequence but I have been unable to and I don't even know if this TV has a test sequence or not. I tried following tom66's instructions in post #3 on this thread https://www.badcaps.net/forum/showthread.php?t=26790. There was no display. Out of curiosity I tried the same method on a working Panasonic TH-50PX75U that I have and was unable to get a test pattern to display on that one either. Do these TVs even have a test pattern?

I did some probing on the two connections between the D board and the A board to see if there was any communication. According to the service manual, connector D3 on the D board has two I2C data busses on it (see attached picture). The data bus labeled "2" has a constant clock signal and data being transferred. However, the bus labelled "1" has no data or clock at all. It is just a constant high signal. I also probed the LVDS lines on connector D5 which connects the D board to the A board. There is no signal on any of these lines at any time. All are 0V.

Since I was not sure what these signals were supposed to look like, I opened up the TH-50PX75U which also had similar pin names on the connections between the DG board and the D board. The data bus labeled "2" also had a constant clock and data signal. However, the data bus labeled "1" had a pulse of clock and data once every second. The LVDS lines between the two boards also had some signals on them at all times, even when the display was blank with no input signal connected.

So it seems to me that the problem may be in the A board as there is no signals being sent to the D board to be displayed. I probed the signals coming from the D board to the upper and lower vertical driver boards and there are similar signals on all pins. I suspect that since the D board is not receiving any inputs, it is defaulting to displaying black on all pixels. I would love to be able to generate my own LVDS signals for the D board to display, but I do not know enough about what protocol or signals the D board is expecting.

I originally suspected the D board as most of the functions that the A board controls are working. Things like the fans, turning the power on and off, receiving remote control signals. However, it seems odd to me that the A board is not sending any signals to the D board through the LVDS cable. I would expect it to be sending something even with a black screen. I would also expect it to send something on power up such as the "first start" menu or the no signal screen. Also, the TV does not self power off due to no signal like all of my other Panasonic displays do. So I am thinking it must be the A board.

Both of the large chips on the D board get quite warm while the TV is running. Not too hot to keep my finger on them, but fairly warm.

Both boards are upwards of $100 on ebay so I would like to be sure which board it is.

The A board is a TNPH0835. The number got cut off in the picture.

Does anyone have any thoughts on which board is at fault here? Or any other things I can test to verify which one it is?

Thanks

[canadaboy25]

Re: Panasonic TC-P54VT25 No image. A or D board?

I should also add that I can connect a video source and use the input select button to blindly navigate to the correct input and I do get working sound. The volume buttons also work as expected.

I can see from the board and the schematic that there a large BGA chip between the main processor chip and the LVDS output of the A board. It seems this chip is for the 3D system on this TV. I wonder if that chip my be causing the problem.

Since there are no test points between the main chip and this 3D chip, my next idea is to scratch off some of the solder mask and test to see if I have LVDS data between the chips if I don't get any replies.

[canadaboy25]

Re: Panasonic TC-P54VT25 No image. A or D board?

Well since my thread is so popular, I figured I'd give everyone an update.

I have attached an image of the portion of the A board containing the main processor on the right, 3D processing chip in the middle, and LVDS connection to the D board on the left.

There is absolutely no LVDS data leaving the A board through the LVDS connector. I scratched away some of the solder resist on the traces between the two chips and tested for LVDS signals there. Sure enough there were constant signals on those lines. So that means the 3D processing chip is not passing the signals through for some reason.

I checked both of the power rails for that chip and they are fine. So either the chip is bad, the solder connections are bad, or the chip is missing some other input causing it to shut down.

The only other signals connected to the chip are:
An I2C bus,
A reset signal,
A JTAG connection,
A NAND flash chip,
A crystal oscillator,
and the IR LEDs for the 3D glasses.

I sort of doubt the chip has just up and died so I will take a look at those other 6 interfaces and see if there is anything clearly wrong. If I don't find the problem I suppose I will try reflowing the chip in case it is bad BGA solder joints.

[canadaboy25]

Re: Panasonic TC-P54VT25 No image. A or D board?

I just came across the technical manual for the 2010 Panasonic plasmas that described a test for the video display circuitry. If the LVDS cable between the A board and the D board is disconnected, the TV should display a white screen, and it does. So I was correct in my diagnosis of the A board. I have done all of the testing I can do on it and it looks like the MIRO-3D chip on the A board has died.