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Vestel 17IPS20P pulsating

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    Vestel 17IPS20P pulsating

    I've got this unlucky board, a Vestel 17IPS20P (150313R3) that got a couples surgeries during its lifetime. The last time I fixed it there was a blown diode (D208), nothing extraordinary, happened already two years ago, changed it and everything was fine. Then after about a month I had the brilliant idea to add the unpopulated diodes D207 and D505 to harden this weak spot. During this operation I must have splattered some solder on the HV section cos after closing the lid and giving power a loud boom happened.

    U202, S536, Q211, R230, R22, R242, D201, D208, D228, D522, D523 were destroyed.

    Removed the extra diodes, replaced these parts and now the board is pulsating. It makes a clicking noise in the region of TR200. VCC_MAIN and VCC_M are trying to reach operational voltage during these pulses. From time to time if you let the board do this thing for a minute or two it may start and give around 10V on +12VCC and 20V on C217, the TV backlight turns on briefly as it should and the red standby led stays on (there is a buzzing noise, maybe caused by the undervoltage). Trying to use the remote to turn on the TV makes it cycle back to pulsating.

    Not sure what to do now, the pulses and the damaged components on the FB_M line could mean a bad U200, but i tried with a 3171 (should be compatible) and nothing changed.
    Attached Files

    #2
    Re: Vestel 17IPS20P pulsating

    Couldn't edit the post, I managed to write the wrong numbers for the damaged components...

    The correct ones are:

    U202, S536, Q211, R217, R242, R228, D201, D208, D522, D523

    Comment


      #3
      Re: Vestel 17IPS20P pulsating

      What value did you use for R228, did you go by the original resistor or the schematic? If d201 was bad, the optocouler may be bad also
      Last edited by R_J; 02-20-2019, 11:19 AM.

      Comment


        #4
        Re: Vestel 17IPS20P pulsating

        Tried with a couple of values: (0,22 - 0,33 - 1) Ohm
        The original resistor was 0,33 , the schematics says 120.
        Did also change the mosfet with a FQPF12N60C, old one was MDF4N65B.

        Comment


          #5
          Re: Vestel 17IPS20P pulsating

          The schematic is wrong, 0.33Ω should be the value, It might be the optocoupler or maybe the reference (U203) got damaged?
          Also check D214

          Comment


            #6
            Re: Vestel 17IPS20P pulsating

            Could try swapping with the octo for the backlight.

            On the pin 3 of the U203 there are pulses of around 340mV, don't know if correct.

            Tried swapping D214, same thing, but there is something strange about VCC_MAIN, it starts at 2V and slowly crawls pulse by pulse but VCC_M, later in the line goes well over 14 V from the beginning.

            Comment


              #7
              Re: Vestel 17IPS20P pulsating

              VCC_M is supplied by U202 (internal startup cell), when the supply starts up, run voltage is supplied from transformer TR200 (pin13) via D214 charging C240. C240 could be bad? it is a common fault for not starting.

              Do you have the main board connected? do you have ST_BY command? it allmost looks like the U202 is in standby mode
              I would think you should have about 7 volts on U203 pin 3, +12VCC, to R236, through U200 (1&2) through R528.
              With ST_BY high, Q204 should be turned on connecting D204 anode to ground
              It could be that U203 is shorted?
              Last edited by R_J; 02-20-2019, 01:04 PM.

              Comment


                #8
                Re: Vestel 17IPS20P pulsating

                Swapped U200 with U301 and replaced C240, same issue.

                At the moment I'm trying with the vestel board alone. ST_BY should be present at all times for the +12VCC to show up? When connected to the logic board the behavior is the same.

                With pin 3 I meant the REF pin, on the node with R255 and R211. But I doubt I'll find anything near 7V, since +12VCC is not present.

                Only the clicking sound is always present, it is somewhat similar to the sound emitted by the electric fence energizers during discharge, a toned down version.

                Comment


                  #9
                  Re: Vestel 17IPS20P pulsating

                  You need to turn the power supply on. or it will be in standby mode. You should be able to connect a 1k resistor between +5V_STBY (standbyvoltage) and ST_BY (power on) Thats CN3 Pin 9 and 3, you may also need a 1k between 9 & 5 BL_ON-OFF to turn on the backlight circuit
                  Last edited by R_J; 02-20-2019, 02:57 PM.

                  Comment


                    #10
                    Re: Vestel 17IPS20P pulsating

                    Maybe this board is a little different from the reference, the section for generating +5_STBY is not populated, Q212 and the surrounding components are missing.

                    Attached the screens on the pin 13 of TR200. Apart from the huge negative spikes there is a positive voltage of 12V. U202 is trying hard to boot up it seems.
                    Attached Files
                    Last edited by otousama; 02-20-2019, 03:21 PM.

                    Comment


                      #11
                      Re: Vestel 17IPS20P pulsating

                      Was your tv always ON or were you able to turn it OFF????? I bet you could turn it off correct? that means the power supply went into STANDBY MODE. Without the ST_BY control signal from the main board the power supply will be in STANDBY MODE!

                      Why won't you believe me????

                      So what does it use for the standby voltage for the main board? Is Q212 bypassed and they use the 12 volts for standby? I don't have a clear picture of the back of the board to tell where the standby voltage comes from.
                      I think they are using the +12 volt line for standby and it likely gets regulated to +5 on the main board. What happens if you connect the main board?

                      TR200 pin 13 is on the hot side, you can not connect the scope ground to the hot ground without an isolation transformer
                      Last edited by R_J; 02-20-2019, 04:02 PM.

                      Comment


                        #12
                        Re: Vestel 17IPS20P pulsating

                        No idea, maybe it's the logic board that controls the ST_BY line once booted?
                        The TV used to fully switch on everytime the mains was plugged, showed the LG logo and 2 seconds later switched off with the red standby light glowing.

                        Q212 doesn't seems to be bypassed, there is no continuity between +12VCC_S and +5V_STBY.

                        I'm guessing that the power supply is not able to perform the initial boot, can't even pull up the +12VCC line, the logic board shouldn't be involved at this stage.

                        This is the back of the board, yes, I've mangled the board after desoldering the same components over and over...

                        At the moment if I connect it to the main board nothing different happens, it's still clicking and failing to pull up the 12V lines.

                        I've used an isolation transformer.
                        Attached Files
                        Last edited by otousama; 02-20-2019, 04:07 PM.

                        Comment


                          #13
                          Re: Vestel 17IPS20P pulsating

                          How does the microprocessor on the main board operate to be able to turn the tv on?????? is there a battery on the main board to do this? NO. it uses a standby voltage from the power supply.
                          The power supply is not ALWAYS ON. it is turned from standby (Burst mode) to full on by a control signal.
                          They must be using the +12 volts CN3 pin 13 for the standby voltage, It is likely about +10 volts in burst mode, which is what you measured. so using a 1k resitor between pin 13 and 3 of CN3 should turn on the power supply

                          Q206 needs to be turned on to turn on Q205 which lights U201 opto, turning on Q216 to supply VCC to U300, U101

                          The logic board is not involved at this stage so the power supply is in standby
                          Last edited by R_J; 02-20-2019, 05:04 PM.

                          Comment


                            #14
                            Re: Vestel 17IPS20P pulsating

                            Originally posted by R_J View Post
                            They must be using the +12 volts CN3 pin 13 for the standby voltage
                            I did mean this with

                            maybe it's the logic board that controls the ST_BY line
                            Anyway, tried with the resistor but no luck, same behaviour, few hundred mV on the 12 V rail.

                            I'll call it a day, thanks for the patience, tomorrow I'll try to poke around some more before using the hammer.

                            Comment


                              #15
                              Re: Vestel 17IPS20P pulsating

                              I thought you were getting 10 volts on the 12 volt rail? if you only have milivolts on the +12VCC_S then the resistor won't work
                              Last edited by R_J; 02-20-2019, 05:19 PM.

                              Comment


                                #16
                                Re: Vestel 17IPS20P pulsating

                                No no, the 12 and the 24 Volt rails are both down, only pulsating a little during the clicks. The only time I saw 10 Volts on the +12VCC rail was after connecting the mains supply and leaving it click for a couple of minutes, it then stopped clicking, turned on the backlight, showed the logo and went in standby. Now, and only now had 10V on the 12v rail, but it was still malfunctioning, there was a buzzing coming from the transformer and the TV did not turn on when the button was pressed, it only started the clicking cycle from the beginning.

                                Comment


                                  #17
                                  Re: Vestel 17IPS20P pulsating

                                  Check that S214 & S215 0Ω are not open, also was R253 still ok?
                                  Last edited by R_J; 02-20-2019, 05:34 PM.

                                  Comment


                                    #18
                                    Re: Vestel 17IPS20P pulsating

                                    Hey there, I've got some news.
                                    The TV is working again, good news! I'm a damn idiot, bad news!

                                    I'm gonna report here my mistakes so that someone else can learn from them.

                                    This morning I tried again to check the U202 surrounding components, with the scope I saw it trying to boot, but it never completed the sequence and remained stuck in a cycle.
                                    Then it struck me... Did I use the correct values for the destroyed components? The schematics is useless in this respect, random values all over the place, so I checked U300 and Q301 and what do you know, the current sense resistor in circuit is 100 Ohm, the schematics says 10 Ohm.
                                    After soldering a 100 Ohm resistor the board came back to life!

                                    Nice, but it doesn't end here, this was only my first mistake.

                                    Thinking I got it finally sorted I soldered back the diodes D207, D208, D209, D210, D211, D505. Powered up and BOOOM.
                                    D207, U202, Q211, FS100, D115, D112 gone. What in the world was happening? It is almost like the first time, everythings working, add a couple diodes and board explodes...
                                    There is where I experience enlightenment (sort of). Im using all SR5100, but originally they were different, expecially the one on the 24V rail! The second mistake was using a schottky barrier with 100V blocking voltage in parallel with a a UF5404. The SR5100 dies instantly after power up and takes with him the HV side of the board (bad design?).

                                    In the end I replaced (again) the damaged components, left UF5404 (D208) alone and the TV is now working.

                                    Thanks R_J for the help, it was a messy fix, I did more harm than good trying to harden the diode section. If it aint broke don't mess with it? Damn right.

                                    Comment


                                      #19
                                      Re: Vestel 17IPS20P pulsating

                                      Well good to here its fixed. That SR5100 is ment for a 60hz power supply, Its not even close to being fast enough for this 132Khz power supply, The UF5404 is a Ultrafast recovery diode. makes a big difference.
                                      I made a note of the resistor value change (R311 = 100Ω) correct
                                      I hate these schematics, they are all over the place with values etc. but, better than nothing.

                                      Comment


                                        #20
                                        Re: Vestel 17IPS20P pulsating

                                        That is strange that R311 has to be 100 Ohms for the circuit to work since the pin 6 Cs has 12K input impedance. R311 and C319 is just simple RC filter.
                                        It is also strange R370 is also shown as 120 Ohms which is really high for current sensing resistor, it is usually <1 Ohms.
                                        The application circuit does show the Pin 6 HAS 100 Ohms resistor and the current sensing resistor (R370 EQ.) is 0.30 Ohms. I wonder if that resistor is wrong as well.
                                        SG6742.
                                        https://cdn.badcaps-static.com/pdfs/...448b95cd95.pdf
                                        Attached Files
                                        Last edited by budm; 02-21-2019, 10:53 AM.
                                        Never stop learning
                                        Basic LCD TV and Monitor troubleshooting guides.
                                        http://www.badcaps.net/forum/showthr...956#post305956

                                        Voltage Regulator (LDO) testing:
                                        http://www.badcaps.net/forum/showthr...999#post300999

                                        Inverter testing using old CFL:
                                        http://www.badcaps.net/forum/showthr...er+testing+cfl

                                        Tear down pictures : Hit the ">" Show Albums and stories" on the left side
                                        http://s807.photobucket.com/user/budm/library/

                                        TV Factory reset codes listing:
                                        http://www.badcaps.net/forum/showthread.php?t=24809

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