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Panasonic Plasma main board repair (ST30 GT30 VT30 ST50 GT50 VT50),LED with 3 blincks

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    Panasonic Plasma main board repair (ST30 GT30 VT30 ST50 GT50 VT50),LED with 3 blincks

    Hi everyone!
    I happened several times, in the search for help from the web, to consult this very interesting forum.
    So I decided to sign up and I intend to participate actively by making available my knowledge and experience on the subject, I'm a new user but at the same time I'm old in the sense that I have 4 decades of experience in repairing and designing electronics but above all I'm a great passionate about the subject.

    Having said that I come to the gist of my post on the forum as the title suggests.
    For my passion for technology I'm now collecting several Panasonic plasma TVs.
    I think the image of these devices is superlative and even considering the era of their launch on the market, they are still difficult to beat in terms of reproduced image quality.
    I can afford the "collection" as this generation of Panasonic plasma TVs are found at very low prices also because I buy them broken in order to repair them purely for personal satisfaction.
    The more you go on with the years, however, the spare parts are increasingly difficult to find and those who have them (I'm talking about complete boards) ask for astronomical amount!
    So I wonder why, as a technician, I have to change the entire board when perhaps the problem is (I say things at random) a transistor or a capacitor worth a few cents that is the cause of the failure???
    Unfortunately, however, this professionalism is disappearing, all you do is change whole boards and throw them in the trash, or faced with absurd amount, you make the decision to throw away and buy the new model again, no one knows how to use a welder and read an electrical diagram anymore to understand the source of the problem.
    In a period like the current one of attention to the environment, I think it is better to repair instead of constantly changing equipment, landfills are overflowing with electronics which in the vast majority of cases could have a new life with the intervention of a repair technician.
    I am addressing the technicians of my generation, I graduated (almost 40 years ago, I also have some gray hair!) as a radio TV repairer, I come from the school of cathode ray tube TV (CRT), a era when it was much easier to fix everything.
    I understand that SMD technology scares a little but the underlying electronics are always the same, you just need to put a little more effort into it then many boards, with the right equipment, in my opinion, can be repaired.
    Specifically, Panasonic provides the service manual which is not bad but the diagrams, at least in the versions that I have found, are "blurred", not very legible and often some parts are missing, such as the power supply.
    I therefore ask for help from someone on the forum who, by profession or other channels, has or is able to provide more information than what is found on the web.
    Specifically I would like to have, if they exist, procedures to better understand where to sift through the schematic to find the fault.
    I'll give an example referring to the title of the post: LED with 3 flashes (TX-P50VT50T, I have two with this problem).
    The service manual says “IROM BOOT PROGRAM SOS”, change board “A” (main board) and/or “P” (power supply).
    But damn! Can't you elaborate on what this “IROM BOOT PROGRAM SOS” means???
    Perhaps by powering the card externally, bypassing some checks, in order to guide the technician to the origin of the problem.
    From what I was able to decipher on the blurred wiring diagrams I checked all the voltages on board "A" (5-3.3-1.8-1.2-1.1) and for a moment, when switched on, they are present then the TV goes into protection and flashes the LED, Vsus and Vda are not shorted, only F15V (15.6V) and the standby 5V (which in my case are 4.4V) remain permanently present.
    I don't believe in self-diagnostics, for me it complicates things and doesn't help solve the causes of the fault, perhaps my opinion clashes with the Panasonic designers but I would just like to have the possibility to investigate further to find out what is broken instead we change the board (which will most likely break again, planned obsolescence) and so we produce waste after waste!

    I hope this speech of mine will interest someone, I thank those who have had the patience to read me up to here, sorry for the inaccuracies of English which is not my native language, I got help from Google to fill my gaps…

    #2
    Re: Panasonic Plasma main board repair (ST30 GT30 VT30 ST50 GT50 VT50),LED with 3 bli

    Ciao....
    The error code explaining sounds like almost surely a software problem, so post a light photo of the main board, no flash, to see if it is present a standby rom or standby uP , one attempt could be rewrite it from dumps took from internet, or by freezing it and reading it fast on the programmer , actually the presence of standby blinkings lets me think that standby sw is good but main sw not. The main sw is on a bigger flash mem.. Panasonic other than service manuals did also repair guides for each plasma series and year.
    Last edited by Davi.p; 11-29-2022, 03:23 AM.

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      #3
      Re: Panasonic Plasma main board repair (ST30 GT30 VT30 ST50 GT50 VT50),LED with 3 bli

      Hi Davi.p!
      Yes there is a EEPROM (24C64F - IC8901), in the pictures you can find it just above the barcode label.
      I have a repair guide found on the web of the US version of the "50" series but it doesn't go beyond checking voltages, it doesn't refer to the firmware...
      Attached Files

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        #4
        Re: Panasonic Plasma main board repair (ST30 GT30 VT30 ST50 GT50 VT50),LED with 3 bli

        it's not that important the 24c EEPROM but the nand flash Toshiba hided in the CAM slot and the IC8601 seems to me a microcontroller for the standby.. to the right i see a chip of about 14pins near a connector, that is probably an rs232 adapter for a debug serial port, it's useful to understand what happens...
        Last edited by Davi.p; 11-30-2022, 02:01 AM.

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          #5
          Re: Panasonic Plasma main board repair (ST30 GT30 VT30 ST50 GT50 VT50),LED with 3 bli

          but for debug I need a software for to see what happens?

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            #6
            Re: Panasonic Plasma main board repair (ST30 GT30 VT30 ST50 GT50 VT50),LED with 3 bli

            normal terminal like hyperterminal

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              #7
              Re: Panasonic Plasma main board repair (ST30 GT30 VT30 ST50 GT50 VT50),LED with 3 bli

              IC8601 from the wiring diagram manages USB and Bluetooth, instead there is an RS232 Driver (IC3851) which comes out on JK3103, the black jack near the blue jack.
              However, this jack seems to be used only to control the TV from a PC (see SM page 11).
              I also attach the block diagram where there are the functions of the various ICs, this part of the SM is not "blurred", the writings instead of the wiring diagrams are mostly indecipherable...
              I add page 10, where it refers to the EEPROM, I don't think it related with the failure but I was wondering what it refers to, are they app "keys"???
              Keep in mind that the command of the famous flashing red LED comes from the central BGA chip (IC8000), I don't know the Panasonic architecture but there doesn't seem to be a microprocessor dedicated to diagnosis, the IC8000 probably supervises almost all the functions of the TV.
              Maybe someone changed it (not a simple work but reballing services exist) and solved the failure???
              Attached Files

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                #8
                Re: Panasonic Plasma main board repair (ST30 GT30 VT30 ST50 GT50 VT50),LED with 3 bli

                The service port minijack is used also for debug but i think that not much is visible due to standby software problem. There is a spi flash but diagram says it is not related to standby microprocessor inside main chip (STM part of Peaks). I think it needs a new bootloader but only factory softwares can do this job.. The second option is that for boot it means boot partition, so try to inform you about usb update..

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                  #9
                  Re: Panasonic Plasma main board repair (ST30 GT30 VT30 ST50 GT50 VT50),LED with 3 bli

                  You can do the classic firmware update via USB but with the TV working, in these conditions I don't think it can be done without knowing "special" modes that only Panasonic can know...

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                    #10
                    Re: Panasonic Plasma main board repair (ST30 GT30 VT30 ST50 GT50 VT50),LED with 3 bli

                    I know that Panasonic (until a few years ago) provided the replacement of this card in exchange, which means that it was easily recovered, in my opinion.

                    The cost was 270€ excluding VAT...

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                      #11
                      Re: Panasonic Plasma main board repair (ST30 GT30 VT30 ST50 GT50 VT50),LED with 3 bli

                      Try for now this, locate the spi flash, freeze it many times with spray, then feed power and turn on, if it doesn't boot desolder it and freeze it just before reading it, save content then write it back when chip not cold. Maybe the chip connected to it (sorry i deleted the attachment, maybe ND6H?) needs a boot too..

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                        #12
                        Re: Panasonic Plasma main board repair (ST30 GT30 VT30 ST50 GT50 VT50),LED with 3 bli

                        Ok I'll try. SPI FLASH is a WINBOND 24Q16CVSIG (IC9304). Panasonic calls it TVRS677AC.
                        A curiosity, have you had experiences of corruption in these SPI FLASH memory?

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                          #13
                          Re: Panasonic Plasma main board repair (ST30 GT30 VT30 ST50 GT50 VT50),LED with 3 bli

                          In tv mainboards is very often, but usuallly those are fed also in standby state, i don't know this how much it is exposed to spikes and other phenomena..

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