when i turn on, Philliips TV is not on

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  • Nish
    Senior Member
    • Sep 2013
    • 124
    • Canada

    #121
    Re: when i turn on, Philliips TV is not on

    Originally posted by R_J
    What are the voltages on IC951? something is wrong in that circuit, that is why there is no regulation happening. Maybe shorted C955,C954? I guess it might be PC901? if you don't have one try exchanging PC902 with PC901.
    IC951= 6.60v I use ground of C951A

    I un solder PC901 now I measure that pads. Still same voltage.

    I replace PC902 with 817A optocoupler. Still same voltage.

    How can I check if C955,C954 are shorted. Can I lift one pad of cap?

    Comment

    • R_J
      Badcaps Legend
      • Jun 2012
      • 9515
      • Canada

      #122
      Re: when i turn on, Philliips TV is not on

      Originally posted by Nish
      IC951= 6.60v I use ground of C951A

      I un solder PC901 now I measure that pads. Still same voltage.

      I replace PC902 with 817A optocoupler. Still same voltage.

      How can I check if C955,C954 are shorted. Can I lift one pad of cap?
      Just check C955/954 in circuit.

      Comment

      • R_J
        Badcaps Legend
        • Jun 2012
        • 9515
        • Canada

        #123
        Re: when i turn on, Philliips TV is not on

        What are the voltages on IC951?

        Comment

        • Nish
          Senior Member
          • Sep 2013
          • 124
          • Canada

          #124
          Re: when i turn on, Philliips TV is not on

          Originally posted by R_J
          What are the voltages on IC951?
          IC951 all 3 pin has 6.60v. But cathode is GND.

          I check both end of cap is 6.60v

          Using ground of C951A
          Last edited by Nish; 01-30-2020, 02:12 PM.

          Comment

          • R_J
            Badcaps Legend
            • Jun 2012
            • 9515
            • Canada

            #125
            Re: when i turn on, Philliips TV is not on

            Originally posted by Nish
            IC951= 6.60v I use ground of C951A

            I un solder PC901 now I measure that pads. Still same voltage.

            I replace PC902 with 817A optocoupler. Still same voltage.

            How can I check if C955,C954 are shorted. Can I lift one pad of cap?
            You needed to replace PC901 NOT pc902 I only suggested exchanging them if you did not HAVE ONE.

            Comment

            • R_J
              Badcaps Legend
              • Jun 2012
              • 9515
              • Canada

              #126
              Re: when i turn on, Philliips TV is not on

              Originally posted by Nish
              IC951 all 3 pin has 6.60v. But cathode is GND.

              I check both end of cap is 6.60v

              Using ground of C951A
              Install a TEMPORARY jumper wire in J14, as the power supply board does NOT connect the negative side of C951A/B to the negative of IC951. WITHOUT this connection, the power supply standby 5 volts has no reference.
              I suspect that the two points only get connected whn the main board is connected, something only Philips would do.
              The grounds I marked in Blue, DO NOT connect to the grounds I marked in Green, this is why the supply has no reference and why the output is too high. Installing the J14 jumper should result in a stable +5 volts.
              Attached Files
              Last edited by R_J; 01-30-2020, 02:37 PM.

              Comment

              • Nish
                Senior Member
                • Sep 2013
                • 124
                • Canada

                #127
                Re: when i turn on, Philliips TV is not on

                Originally posted by R_J
                You needed to replace PC901 NOT pc902 I only suggested exchanging them if you did not HAVE ONE.
                Sorry I miss type. I replaced PC901. By the way I will replace c954. But value is 0.1, is that uF or nF?

                Comment

                • R_J
                  Badcaps Legend
                  • Jun 2012
                  • 9515
                  • Canada

                  #128
                  Re: when i turn on, Philliips TV is not on

                  Originally posted by Nish
                  Sorry I miss type. I replaced PC901. By the way I will replace c954. But value is 0.1, is that uF or nF?
                  Had you told me the voltages on IC951 earlier, I would not have suggested the capacitorsT he caps will be ok, Install the jumper wire I suggest this will fix this issue.
                  Last edited by R_J; 01-30-2020, 02:40 PM.

                  Comment

                  • Nish
                    Senior Member
                    • Sep 2013
                    • 124
                    • Canada

                    #129
                    Re: when i turn on, Philliips TV is not on

                    Originally posted by R_J
                    You needed to replace PC901 NOT pc902 I only suggested exchanging them if you did not HAVE ONE.
                    Sorry I miss type. I replaced PC901. By the way I will replace c954. But value is 0.1, is that uF or nF?

                    Comment

                    • R_J
                      Badcaps Legend
                      • Jun 2012
                      • 9515
                      • Canada

                      #130
                      Re: when i turn on, Philliips TV is not on

                      Originally posted by Nish
                      Sorry I miss type. I replaced PC901. By the way I will replace c954. But value is 0.1, is that uF or nF?
                      Why??? Just put the original one back in. THEN add the jumper Like I suggested. Look at the schematic... then check the resistance between C951 ground and ic951 ground. If the grounds are not connected together how can it work?
                      The cap is likely .1ยตf
                      Last edited by R_J; 01-30-2020, 03:16 PM.

                      Comment

                      • Nish
                        Senior Member
                        • Sep 2013
                        • 124
                        • Canada

                        #131
                        Re: when i turn on, Philliips TV is not on

                        Originally posted by R_J
                        Had you told me the voltages on IC951 earlier, I would not have suggested the capacitorsT he caps will be ok, Install the jumper wire I suggest this will fix this issue.
                        I am outside now, I will do the jumper and update later. Thanks

                        Comment

                        • Nish
                          Senior Member
                          • Sep 2013
                          • 124
                          • Canada

                          #132
                          Re: when i turn on, Philliips TV is not on

                          Originally posted by R_J
                          Install a TEMPORARY jumper wire in J14, as the power supply board does NOT connect the negative side of C951A/B to the negative of IC951. WITHOUT this connection, the power supply standby 5 volts has no reference.
                          I suspect that the two points only get connected whn the main board is connected, something only Philips would do.
                          The grounds I marked in Blue, DO NOT connect to the grounds I marked in Green, this is why the supply has no reference and why the output is too high. Installing the J14 jumper should result in a stable +5 volts.
                          I install jumper at J14. The C951A ground and IC951 ground are connected together. Now I have IC901 cathode is 6.60v and ref is 1.4v. PC901 still pin 1 and 2 are 6.20v.

                          I checked around IC951
                          R955 = 1.4v
                          C955 = 1.4v (which is connected to ref of IC901)
                          C954 = 1.4v (which is connected to ref of IC901)

                          ZD907 = -5v
                          Last edited by Nish; 01-31-2020, 11:47 AM. Reason: Add details

                          Comment

                          • Nish
                            Senior Member
                            • Sep 2013
                            • 124
                            • Canada

                            #133
                            Re: when i turn on, Philliips TV is not on

                            Originally posted by R_J
                            Why??? Just put the original one back in. THEN add the jumper Like I suggested. Look at the schematic... then check the resistance between C951 ground and ic951 ground. If the grounds are not connected together how can it work?
                            The cap is likely .1ยตf
                            Yes I put back the original one

                            Comment

                            • Nish
                              Senior Member
                              • Sep 2013
                              • 124
                              • Canada

                              #134
                              Re: when i turn on, Philliips TV is not on

                              Is there anything I can do further with this board?

                              Comment

                              • R_J
                                Badcaps Legend
                                • Jun 2012
                                • 9515
                                • Canada

                                #135
                                Re: when i turn on, Philliips TV is not on

                                Originally posted by Nish
                                Is there anything I can do further with this board?
                                Did you ever replace C951? The feedback circuit is very simple I don't know what could be causing it not to work, Have you checked that all the resistors have the correct resistance, even R952.
                                R954 and R955 set the voltage for the reference pin on ic951. If the voltage on C951A is too high (or has too much ripple) IC951 should start to conduct and lower the voltage on PC901 pin2, this lights the led in PC901 telling ic901 to lower the voltage, this is how it regulates.
                                As you can see, if the feedback is not working, IC901 operates full, and the result is too high a voltage on ZD951/C951A. If it was'nt for ZD951 (6.2v zener) clamping that voltage it could be 10 volts or more.
                                The problem is in that feedback circuit.

                                Comment

                                • Nish
                                  Senior Member
                                  • Sep 2013
                                  • 124
                                  • Canada

                                  #136
                                  Re: when i turn on, Philliips TV is not on

                                  Originally posted by R_J
                                  Did you ever replace C951? The feedback circuit is very simple I don't know what could be causing it not to work, Have you checked that all the resistors have the correct resistance, even R952.
                                  R954 and R955 set the voltage for the reference pin on ic951. If the voltage on C951A is too high (or has too much ripple) IC951 should start to conduct and lower the voltage on PC901 pin2, this lights the led in PC901 telling ic901 to lower the voltage, this is how it regulates.
                                  As you can see, if the feedback is not working, IC901 operates full, and the result is too high a voltage on ZD951/C951A. If it was'nt for ZD951 (6.2v zener) clamping that voltage it could be 10 volts or more.
                                  The problem is in that feedback circuit.
                                  Sorry, I didn't have internet for 3 days....
                                  No I didn't replace C951.
                                  R952 = 1.991k
                                  R954 = 6.01k
                                  R955 = 2.951k
                                  "*set the voltage for the reference pin on ic951." Am I using external power supply at what voltage, while the board plug in the outlet? I am confused

                                  Comment

                                  • R_J
                                    Badcaps Legend
                                    • Jun 2012
                                    • 9515
                                    • Canada

                                    #137
                                    Re: when i turn on, Philliips TV is not on

                                    What I said was that R954 and R955 set the voltage for the reference pin on ic951, thats how the those reference ic's work. R954 and R955 form a voltage divider, So when the voltage on the top of R954 increases, the voltage on the other end of R954 increases, this will cause IC951 to turn a bit more lowering the voltage on PC901 pin 2.
                                    But this is not happening so the led in PC901 never turns on.

                                    Comment

                                    • Nish
                                      Senior Member
                                      • Sep 2013
                                      • 124
                                      • Canada

                                      #138
                                      Re: when i turn on, Philliips TV is not on

                                      I have replaced R954. Now the voltage attached images.
                                      Across ZD907 = -3.0v
                                      Across C906 = 16.20 solid
                                      Across C912 = 11.21 solid
                                      Across C951A =5.38
                                      Attached Files

                                      Comment

                                      • R_J
                                        Badcaps Legend
                                        • Jun 2012
                                        • 9515
                                        • Canada

                                        #139
                                        Re: when i turn on, Philliips TV is not on

                                        That looks like it is working ok. Now check the voltage across C906 to see what it reads. To turn on the rest of the power supply you would need to connect P-ON-N1 to AL+5V
                                        Last edited by R_J; 02-06-2020, 04:55 PM.

                                        Comment

                                        • Nish
                                          Senior Member
                                          • Sep 2013
                                          • 124
                                          • Canada

                                          #140
                                          Re: when i turn on, Philliips TV is not on

                                          Across C906 = 16.20 solid

                                          Comment

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