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LCD Philips 47PFL4606H/12 - power supply doesn't start, no voltages

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    #21
    Re: LCD Philips 47PFL4606H/12 - power supply doesn't start, no voltages

    The voltage on C907 will only be 313 volts because the pfc boost circuit is not working. And it won't operate untill you get the standby circuit working. You need to have (maybe 25 volts) across C946 to have ic905 working.
    This is where a scope works really well, but without it... we must assume ic905 is trying to start and ouputing pulses on the drain (pin6)
    If it is, there should be a HF a/c voltage on pin #4 of T904, If R959, D916 & C946 are ok there should be about 25 volts on C946.
    Have you tried replacing C946 & C943?

    It seems like there should be an initial voltage that comes via C910, R967, D904, through zd912, R951, zd908, R922, based on the ic's pdf, this voltage needs to be at least 6 volts before the ic even starts

    I would check all the zener diodes in that circuit and even the resistors.

    Before ic901 and ic902 can operate they need VCC, The source of the vcc (Vdd-S) is via switch Q907 collector and the source voltage for Q907 emitter is from C946.
    Last edited by R_J; 04-08-2019, 02:41 PM.

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      #22
      Re: LCD Philips 47PFL4606H/12 - power supply doesn't start, no voltages

      Thanks for that info, gives me plenty to work with in isolating the fault. Im just waiting on delivery of some components ( unfortunately no tech shop nearby) and hopfully get it sorted in the next few days. Will let you know how it goes

      Frank

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        #23
        Re: LCD Philips 47PFL4606H/12 - power supply doesn't start, no voltages

        I just noticed zd 912 & r965 are not fitted & the schematic notes them as NC ( no connectio I assume) What do you think is the alternative supply path to pin 1 on the ic905. there is only 1.5 v on it, not enough to start the ic. Pin 6 has 313v. Note there is 150v accross c910.

        I have replacedcaps c943 & c946.

        Would appreciate if you have further ideas

        Thanks Frank

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          #24
          Re: LCD Philips 47PFL4606H/12 - power supply doesn't start, no voltages

          You say you get 150v across C910, Is that actually across it or from hot ground to each side of the cap?
          The X pin2, can be used for on/off, so what is the voltage on Q13, base and collector, maybe it has the ic turned off? I would think the voltage across ZD909 should be 9 volts, It could be that the zener is zenering at 2.7 volts and not 9v
          Last edited by R_J; 04-12-2019, 10:50 AM.

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            #25
            Re: LCD Philips 47PFL4606H/12 - power supply doesn't start, no voltages

            Hi, thanks for quick reply
            Latest checks, using hot - ground.
            Q913, B = 0v. E = 0.45v, collector is connected direct to hot ground. (other side of r931 = 0.54v) so must be a small current flow there.

            I rechecked c910 each side in relation to hot ground. 110v & 2.7v ( so 108v axross the cap.). I also replaced zd 909 with a 9v1 still reads 2.7 v across.

            I wonder if c947 c948 could be a problem although there not shorted.

            Also the suspect ic i removed seems to have a very low resistance between pin3 and ground pins 8ohms which is not the case on the new ic. So if it got dammaged what dammaged it.

            Hope the above may help towards isolating the problem

            Frank

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              #26
              Re: LCD Philips 47PFL4606H/12 - power supply doesn't start, no voltages

              If it is of any help to anyone, I'm repairing this board at the moment and found ZD907 (9V1) shorted.
              Replaced it but no change. The resistance between pin 3 of the IC and live ground is very low as well - around 7.5 Ohms. So I'll order the IC and wait for it to arrive. Hopefully, it will work.

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                #27
                Re: LCD Philips 47PFL4606H/12 - power supply doesn't start, no voltages

                Dear friends from badcaps!!!!
                I also have had some troubles with the same Philips 47PFL4606H/12 TV...:: The fault was slightly different: once plugged in, the tv remained dead, with no led lit, until you unplug and reconnect the plug from the mains, sometimes several times.... It was a friend's tv and I did not test it for longer....
                I have found that when the tv did not start, the 5V voltage line stayed low, around 4,70V and the 3,3V was missing on the PSU (715G4546-P03-H20-003U)... When the tv did accept to start the 5V was higher, around 5,1V, and the 3,3V was present on the PSU... I have found that this 3,3V was coming from the SSB, through a 5V-3,3V voltage regulator and allowed by a transitor ( BC847C) whose base current was coming from the processor of the SSB... The base current was bringing down the 3,3V to 0,02V when the did not start. I was nearly to give up when I had the idea that I could help the processor to perform better its job by renewing its surrounding caps. To my surprise, this has solved this weird problem: the 3,3V is always present and the processor does not bring it down anymore by sending a base voltage to the BC847C NPN transistor, Q703.....
                I hope that this experience may help some of you....

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                  #28
                  Re: LCD Philips 47PFL4606H/12 - power supply doesn't start, no voltages

                  I have also repaired a thunderstruck 42PFL4606H with the same symptoms as in the original post. Initially standby voltage was 0.0 volts; after replacing IC905 (TOP264), ZD907 and Q906 it rose to 0.5 volts.

                  After that I could no longer measure any broken semiconductors so I tried if there was something wrong with the protection circuits of the standby SMPS and shorted IC905 pins 1 and 2 to primary ground. Then I got +5 V on the standby line. After a more careful analysis I removed the shorts and found out that removing R922 did the trick but I am not super happy about the fact that I don't understand by it was working prior to the over-voltage incident.

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