FPGA not reading firmware from flash on Panasonic TC-P54VT25 Plasma main board - Page 1
Forum section: electronics / repair

author: canadaboy25
author_rank: Regular Contributor
timestamp: January 18, 2021, 06:37:38 am
content: Hey everyone,Below is a detailed description of my troubleshooting process for how I arrived at the question I am asking. If this does not interest you or is not important, please skip to the paragraph with the bolded first sentence for my question.I am working on a Panasonic plasma TC-P54VT25 that turns on and primes the display, but no video data is getting to the display.As pictured, there is a main board referred to as the "A" board with all of the video inputs on it. This board does the video signal processing and outputs the LVDS video data through the ribbon cable to the board in the center of the TV referred to as the "D" board. The D board then sends the signals out to all of the buffer boards along the top and bottom of the panel. By my logic and the service manual troubleshooting guide, the problem lies in either the A board or the D board.I started by applying a video source and was able to blindly navigate to the correct input and get sound output. The test video signal is a solid blue screen from a VCR, and I used my phone to play music so I could hear when the correct input was selected. With this setup I should be getting LVDS signals from the A board to the D board through the ribbon cable. However, I am getting no signal on any lines. This seemed to be the problem.I then focused my attention on the A board. As can be seen in the attached screenshot of the service manual. There is a large BGA chip IC8000 on the right that does most of the processing. There is then a smaller BGA chip IC5800 in the middle of the image which inputs the LVDS display signals from the main chip and outputs the LVDS signals to the D board. This chip also controls the IR LEDs for 3D glasses on the front of the TV as this is a 3D capable TV. I probed the LVDS signal lines between the two chips and there were signals. So my problem is in the 3D driver chip IC5800 as it is receiving signals but not sending them out to the D board to be displayed.So either the chip itself is bad, the soldering is bad, or it is missing some inputs it expects.I painstakingly mapped out all of the pins on this BGA chip from the service manual. There are 2 power rails which are ok, many grounds and unused pins, and the LVDS signal connections. Aside from all of these pins, there are only 6 other interfaces connected to this chip.There is:A crystal oscillator,A reset signal,An I2C interface,A JTAG interface,The IR LED interface for the 3D system,A flash memoryThe relevant pages of the service manual are 61 and 62. I have attached these pages individually for convenience.I started checking each of these interfaces.The crystal oscillator is oscillating at the rated 27MHz.The JTAG interface is not connected to anything and was likely used in the factory.The reset signals go high or low on startup depending if the are active high or active low and then go to their default values.I wouldn't think the IR LED interface wouldn't stop the TV from running and to be sure I disconnected it. No change.I am not sure how to test the I2C bus other than making sure it isn't shorted (it isn't), as it connects to many different chips and I am not sure what data should be on this bus.This left the flash memory.This is where I think I may have found a problem. I have attached an image of the flash memory section from the service manual. It is a fairly simple interface with a clock, cable select, serial in, and serial out line. I probed the clock signal at startup and while the TV was running and there is never a clock signal. The clock line is always at 0V. There are no shorts on the line and the resistor is in tact. The other 3 lines are always at 3.3V. There is no data or clock on this interface at any time.I assume that this chip is an FPGA which would need to load its firmware from flash at startup. However, it never reads anything from this flash memory which would explain why it does absolutely nothing and prevents the TV from working. However, I am at a loss as to why it never reads the flash. The clock line comes straight from the FPGA through a resistor to the flash memory chip. The pulldown resistor is also not shorted and in spec.Am I correct in assuming that this chip is an FPGA? Googling the part numbers NEC D811305F1611 1025LU601 provides nothing. I would think it is an FPGA since it has many unused pins which I would not think would be the case for a custom ASIC?If this is in fact an FPGA, what could be causing it to not read the firmware from the flash chip? Why would there be no clock signal?Please let me know what you think and any advice you may have.Thanks

author: canadaboy25
author_rank: Regular Contributor
timestamp: January 18, 2021, 06:41:13 am
content: Here is an image of the A board, all the attachments were too large for one post.

author: canadaboy25
author_rank: Regular Contributor
timestamp: January 18, 2021, 07:16:59 pm
content: Another update.The I2C bus connected to the 3D chip has no activity on it at all. This bus connects to the large main BGA chip, the 3D BGA chip and an ASIC controller on the A board.Both of the I2C lines are high so the pull up resistors are in tact. There is just no activity.I'm not sure if this indicates a problem as I do not know enough about how all of these chips are supposed to communicate with each other.Here is the block diagram view of the 3D chip. The flash connects to the chip to a point labelled CPU BUS I/F.Anyone have any ideas?

author: TheMG
author_rank: Frequent Contributor
timestamp: January 19, 2021, 01:40:15 am
content: Quote from: canadaboy25 on January 18, 2021, 06:37:38 amI don't think it is. NEC as far as I know wasn't ever really into making FPGAs, but they did manufacture ASICs for a very wide number of product manufacturers.It likely is some sort of ASIC. Depending on the processes used, it may have been cheaper and easier to use external flash memory than to incorporate it into the ASIC.As for the unused pins, they may have chosen a larger package than necessary in order to make it easier to route the LVDS signal traces, which have to be of equal electrical length. It may have been cheaper to do this than to use a smaller BGA package that could have required additional layers in the PCB.Quote from: canadaboy25 on January 18, 2021, 07:16:59 pmYour guess is as good as mine. Without having datasheets for the chip, or more detailed information in the service manual describing the purpose of each IC and each signal (sadly, the service manuals these days are mostly limited to board-swapping, lucky if they even provide schematics), it's going to be pretty hard to figure out.The best thing would be to have a working TV of the same model, or at least a known working board, to measure signals and compare. But at that point you're probably better off getting a replacement board and calling it done.

author: canadaboy25
author_rank: Regular Contributor
timestamp: January 19, 2021, 02:24:28 am
content: Ah I see. That makes sense about the unused pins.I also have realized that the external flash likely does not hold a firmware. There are other I2C busses connected to EEPROM chips which are read every time the TV is plugged into power. This seems much more like a chip holding a firmware. These chips are labelled EEPROM while the chip in question is labelled FLASH. So I am thinking it is likely used to store some sort of service menu settings perhaps.The I2C bus has no data on it at any time. I am guessing that it is not supposed to as I'm fairly certain the main CPU chip is functioning fine and it would likely be the master. In that case I should see an address being sent out and no ACK if the communication wasn't successful. Other than the I2C bus, this flash chip, and the 3 reset signals, there is no other logic being sent to this chip. The power rails are both present and the incoming LVDS data is there so my best guess is that the chip is bad or there is a bad BGA ball on an important power pin.Out of curiosity, I will pick up a board on ebay and then probe the two interfaces to see what they are supposed to look like. My suspicion is the chip itself at this point.