Need help on replacing diodes..

Collapse
X
 
  • Time
  • Show
Clear All
new posts
  • Duncanbest
    Senior Member
    • Jul 2012
    • 81
    • Taiwan

    #21
    Re: Need help on replacing diodes..

    The SM link

    Comment

    • JonathanAnon
      Badcaps Veteran
      • Jul 2012
      • 457
      • Ireland

      #22
      Re: Need help on replacing diodes..

      Just downloaded that, Duncan, that will be really useful thanks.. couldnt find it in any of my google searches.. I'll search that site in future.

      Comment

      • JonathanAnon
        Badcaps Veteran
        • Jul 2012
        • 457
        • Ireland

        #23
        Re: Need help on replacing diodes..

        Hi lads, just a quick update.. I had the power board here out of the TV, cos it was too cold to work in my workshop, and the TV is too big to bring in.. I tested alll the components that are usually replaced with repair kits and the like and all checked out okay.. I soldered a few dodgy looking joints..

        Put the board back in the next day and the standby light came on. I checked all of the 5v and 3.3v standby voltages from the schematic above and all are working....

        I'm a bit confused by this, cos I dont think that anything I did "fixed" the standby issue.. But I do remember that the inverter board cable was not attached when I opened the TV originally, so it is possible that the standby light was simply not connected (giving me the impression that there was no standby)..

        I'm gonna move on to checking where the startup voltage is passed from the front buttons to the VGA board to the PSU and see if it is receiving the turn on signal.. I'll keep ye posted.. :-)

        Comment

        • JonathanAnon
          Badcaps Veteran
          • Jul 2012
          • 457
          • Ireland

          #24
          Re: Need help on replacing diodes..

          Hi lads, I got to spend a few hours at this again today.. very frustrating..

          Like I said above I'm at the stage where I have full standby (all standby voltages and standby light), but not switching on... I have no remote, the chap I'm helping fix it for said that he press the button panel on the side of the TV to control it... He said that the Program+ button starts the TV.

          I'm trying to track the BL_ON / POWER ON from the button panel to the front to the PSU. I've traced the buttons back to a connector on the main board.. (schematic below)

          http://www.eserviceinfo.com/download...0TFT%20TV.html


          The button panel connects to two pins on the main board. The voltage across this is 0.8V, and changes to 0.35V when I press the Program+ button. But I cant find where this signal is passed FROM the main board TO the PSU. I have measured ALL the voltages across all the outputs pins from the main while pressing the Program+ button, but nothing happens.. any suggestions?

          Comment

          • tom66
            EVs Rule
            • Apr 2011
            • 32560
            • UK

            #25
            Re: Need help on replacing diodes..

            Perhaps bad firmware or somehow microcontroller not starting.
            Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
            For service manual, schematic, boardview (board view), datasheet, cad - use our search.

            Comment

            • JonathanAnon
              Badcaps Veteran
              • Jul 2012
              • 457
              • Ireland

              #26
              Re: Need help on replacing diodes..

              Originally posted by tom66
              Perhaps bad firmware or somehow microcontroller not starting.
              Hey tom.. yeah I guess that the next thing would be to test the input pins of the MCU to see if it is receiving the signal. I have a pretty good schema for that main board so I'll try find it...

              I know for the LCD monitors that the BL_ON is usually about 5V.. What should I expect to see roughly coming from the main board to the PSU to trigger the BL_ON?

              Comment

              • JonathanAnon
                Badcaps Veteran
                • Jul 2012
                • 457
                • Ireland

                #27
                Re: Need help on replacing diodes..

                PIN 49 on the SDA5550M MCU is called PDP_GO1/BL_ON_OFF



                I'll check and see what happens on this pin when I hit the button on the front.

                Comment

                • JonathanAnon
                  Badcaps Veteran
                  • Jul 2012
                  • 457
                  • Ireland

                  #28
                  Re: Need help on replacing diodes..

                  oh man, those pins are tiny... I've traced where the voltage from the panel buttons come back to the pins of the MCU and the path is okay, but I'm afraid to put the multimeter across the pin 49 above... The probes are too big...

                  I tried to be a smart lad and find where the next component on the path from pin 49 is and measure from there, but I cant find where it goes... Anything I can do about (safely) getting my probe on the small pin..

                  Comment

                  • tom66
                    EVs Rule
                    • Apr 2011
                    • 32560
                    • UK

                    #29
                    Re: Need help on replacing diodes..

                    Where's R693? Probe there.
                    Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
                    For service manual, schematic, boardview (board view), datasheet, cad - use our search.

                    Comment

                    • JonathanAnon
                      Badcaps Veteran
                      • Jul 2012
                      • 457
                      • Ireland

                      #30
                      Re: Need help on replacing diodes..

                      Originally posted by tom66
                      Where's R693? Probe there.
                      I couldnt find it tom. I spent quite a while looking for it, and checking for continuity from pin 49 to ALL the nearby components, but I can find where it connects to.. hence, I dont see any other option but putting a probe on the pin itself..

                      And I just know what's gonna happen if I try this, I'm gonna short it out against one of the adjacent pins..

                      Comment

                      • JonathanAnon
                        Badcaps Veteran
                        • Jul 2012
                        • 457
                        • Ireland

                        #31
                        Re: Need help on replacing diodes..

                        Made a bit of progress today.. I confirmed that the signal from the panel buttons reaches one of the bottom pins on the MCU..

                        Turns out R693 was on the other side of the board.... So I put the black lead to cold ground and the red lead to R693... It read 1.42V (on the near side to the MCU) and did change from this value when the panel buttons were pressed..

                        Comment

                        • JonathanAnon
                          Badcaps Veteran
                          • Jul 2012
                          • 457
                          • Ireland

                          #32
                          Re: Need help on replacing diodes..

                          Just digging up this thread again, as I need to make a decision on what to do about this screen.. I've been mulling it over and I cant decide what to do...

                          Essentially a brief is as follows:
                          - TV wont switch on.
                          - Standby voltage works fine.
                          - Buttons on front work fine.
                          - Button power on signal reaches pin of MCU on video board but no BL_ON signal is passed from the other side of the MCU. Standby voltages on power input pins of MCU seem okay also.
                          - So it seems that the problem is with the MCU (or EEPROM)

                          so I'm faced with the option now of chance buying a new video board (I can get one for 50 euros online) and hope that there is nothing wrong with the inverter board and the screen.. Is there anything else I should try before taking a leap of faith..

                          Comment

                          • JonathanAnon
                            Badcaps Veteran
                            • Jul 2012
                            • 457
                            • Ireland

                            #33
                            Re: Need help on replacing diodes..

                            Bought the 17MB15E-3 board for 30 quid online.. threw it in, and the main relay is now clicking on... It shuts down immediately, but it's nearly enough for me to know that I was right about the video board :-)

                            Gonna get stuck in to it again over the next week.

                            Comment

                            • JonathanAnon
                              Badcaps Veteran
                              • Jul 2012
                              • 457
                              • Ireland

                              #34
                              Re: Need help on replacing diodes..

                              Sorry for digging this up again... but I went at it again today, and it turns out that it IS actually working. The relay was clicking off because the TV was actually switched off.... I turned the TV on to it's back and hit the channel up button and the screen lights up...

                              So in summary: it was the video board... standby voltage was reaching the MCU, and the signal from the control panel was also reaching the MCU inputs... BUT the MCU was not switching on. I replaced the video board with a good MCU and she powers on .... thanks to everybody who helped.

                              Comment

                              Related Topics

                              Collapse

                              • caspian
                                What Zener Diodes on a Linear Power Supply
                                by caspian
                                Dear members,

                                I have a linear variable power supply with unknown brand name that I used for voltage injection.
                                Then it failed. I discovered that its transistors (Q1 and Q2) are shorted.
                                In addition, I discovered that its zener diodes are defective.
                                I can replace the burned transistors.
                                But I do not know the model of the zener diodes. the model number is not marked on the zener diodes.
                                Therefore, I cannot replace the zener diodes.
                                I do not want to test the zener diodes in a test circuit to discover their model or value.
                                no schematics are available...
                                05-26-2025, 12:38 PM
                              • nicktasios
                                Macintosh Quadra 840AV PSU
                                by nicktasios
                                I had my Quadra 840AV (which I recapped and had working) plugged in for some time without using it and randomly decided to turn it on today. Unfortunately it did not turn on. After checking the PSU, I found out I was not getting anything from 12V, only from the 5V rail. After a few minutes, I removed the PSU and plugged it back in the electrical outlet and it suddenly started making a weird sound and soon after smoke started coming out. I quickly unplugged it. I opened it up but on first instance I didn't see anything out of the ordinary really. I later turned it back on and one of the MOVs blew...
                                12-22-2024, 05:07 AM
                              • Crystaleyes
                                Inverter Welder Strangeness
                                by Crystaleyes
                                Hola peeps.

                                I'm placing it in this topic, because from what I can see, it is essentially a modified SMPS, but please move if there is a 'correct' forum section.


                                Recently, I bought an essentially brand new, but defective, 155 amp inverter welder.

                                The unit would turn on fine, with the digital display and fan doing their thing, however when attempting to strike an arc, the rod would merely spark or just get stuck onto the steel.

                                Now I know that many (if not most) in here would simply not have bought it, but I am still learning this trade...
                                03-27-2023, 04:04 PM
                              • DjKrish
                                replacing schottky diodes on a AV power supply
                                by DjKrish
                                Hi guys, i have a power supply with a shorted SR320 schottky diodes which is in parallel. Only 1 shorted while another is ok. So i removed the faulty one, the power supply is working fine now. SR320 is 3A 20V. I was thinking can i remove both diodes and replace SR340 as 1 diode as it is 3A 40V? Because i dont have SR320. Or can i replace both with SR340?
                                08-28-2020, 01:31 AM
                              • Steph.hen
                                Bridge rectifier identification part number KPB305G
                                by Steph.hen
                                Hi all, a newby question about a bridge rectifier I'm trying to identify.

                                I'm in the midst of reparing a battery charger in work which went pop, The bridge rectifier has shorted and took out a couple of other components. The rectifier in question has a part number KPB305G, and it looks like it's obsolete. Does any one know what I could replace it with?...
                                08-29-2024, 09:52 AM
                              • Loading...
                              • No more items.
                              Working...