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Vizio VW37 Power Supply PSON working but no 12v or 24v output

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    #41
    Re: Vizio VW37 Power Supply PSON working but no 12v or 24v output

    I think it is just the photo that makes the U6 soldering joints look a bit bad.

    As for D4, I don't want to get my hopes up just yet (I have done that many times previously throughout this process), but I think it may be faulty.

    With my multimeter set to the diode check function it reads (and the power off):

    .177 VDC with the red probe on the ground side (left side in the photo)
    .607 VDC with the black probe on the ground side (left side in the photo)

    Is this diode the problem?

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      #42
      Re: Vizio VW37 Power Supply PSON working but no 12v or 24v output

      Could be leaky, causing low output voltages. (Diodes usually fail short circuit, but sometimes before failing completely, they become leaky, conducting both ways but still retaining some kind of polarity.) You'll need to very carefully lift one side of it, and re-test.

      Refer to the faint grey polarity band (closest to the buck converter) when talking about the polarity; the band indicates the negative end of the diode.
      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.

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        #43
        Re: Vizio VW37 Power Supply PSON working but no 12v or 24v output

        Could you explain "lift one side of it"?

        Is this to test it while it is disconnected at one side? Is it just an easy way to do an out of circuit test, without the extra de-soldering?

        Comment


          #44
          Re: Vizio VW37 Power Supply PSON working but no 12v or 24v output

          Originally posted by Tetranitrate View Post
          Could you explain "lift one side of it"?

          Is this to test it while it is disconnected at one side? Is it just an easy way to do an out of circuit test, without the extra de-soldering?
          Yeah, just use the soldering iron to remove one side from the board. No complete circuit now, the rest of the circuit can't change the results. Recommend you try the IC side as this will be easier, less of a PCB heatsink. If it's easier for you, you can just remove the entire diode, but it's quite hard to probe a tiny SMD thing like that with standard multimeter probes and much easier to do it with the board holding it down.
          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.

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            #45
            Re: Vizio VW37 Power Supply PSON working but no 12v or 24v output

            With it disconnected on the chip side, the drop is .175 with the red probe on the ground side, and no reading (OL) with the black probe on the ground side.

            Comment


              #46
              Re: Vizio VW37 Power Supply PSON working but no 12v or 24v output

              Originally posted by Tetranitrate View Post
              With it disconnected on the chip side, the drop is .175 with the red probe on the ground side, and no reading (OL) with the black probe on the ground side.
              That indicates a functional diode.

              What is the part # of the switchmode controller?
              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.

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                #47
                Re: Vizio VW37 Power Supply PSON working but no 12v or 24v output

                AP1513 (Datasheet attached)

                Also attached is a photo of how the diode was tested, that also shows U6 more clearly.

                The input Vcc has to be higher than what the output of the chip is, right? Is there any way to know what the chip should be receiving at Vcc? If I knew that would I be able to work backwards to where the voltage is correct?
                Attached Files

                Comment


                  #48
                  Re: Vizio VW37 Power Supply PSON working but no 12v or 24v output

                  That's the right way to test the diode. Make sure to install it properly now as it should be fine.

                  Measure the resistor values next to pin #1, these determine output voltage.

                  Pin #2 should be >2.0V to turn the converter on, check this is the case.
                  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.

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                    #49
                    Re: Vizio VW37 Power Supply PSON working but no 12v or 24v output

                    R39 (RA on the schematic) reads .868kΩ, and R42 (RB on the schematic) reads .83kΩ

                    I added these values to the attached filled in schematic.

                    According to the service manual, both of these resistors should be 1kΩ.

                    Pin 2 is at 1.072V
                    Attached Files

                    Comment


                      #50
                      Re: Vizio VW37 Power Supply PSON working but no 12v or 24v output

                      On the second to last page of the chip datasheet, it says that the chip uses "under voltage lockout". If the Vcc falls below 3.3 volts then lockout will occur. It seems like pin #2 is low because my Vcc is low (1.09v).

                      I have attached an updated typical application circuit, Vcc and EN are related to each other by REN. In their theoretical sample circuit REN is listed as being 20kΩ. I just measured REN (R41) as 100.5kΩ, which matches up with what is should be according to the Vizio service manual (100kΩ).

                      So if the low Vcc is the culprit, then I need to track that down, but am having a hard time finding out where it originates on the board.
                      Attached Files

                      Comment


                        #51
                        Re: Vizio VW37 Power Supply PSON working but no 12v or 24v output

                        So I have been staring at this portion of the circuit for a few hours trying to find traces that lead into Vcc or out of Vout and I have not been able to find anything.

                        Would it make sense to have a portion of a circuit like this completely isolated from everything except for the ground plane? From what I can tell there are no traces that lead into this portion of the circuit or out of this portion of the circuit.

                        I have attached an image with the isolated are circled in yellow. There are five traces that pass by on the bottom right portion of the circuit, but (as far as I can tell, although I am pretty certain) they do not connect with it. On the underside of the circuit board there is connection between the positive portion of CE15 and L8. The negative lead of CE15 is tied to the ground plane on the underside of the board, but besides that there are no other connections.

                        I have also included an even further updated schematic diagram of this portion of the circuit, which I think is correct, although I am not sure about Cin or CVcc, the values for those two might be reversed. CB27 and L16 are not included in my ms paint schematic, because I am not sure where they would go.

                        I can't imagine the purpose of having something completely isolated from everything but the ground plane, unless it is some sort of circuitry to keep watch on the ground, and make sure there are no stray voltages or currents floating about.

                        I really hope this makes sense to someone who reads it, because I am at a loss for how this magical portion of the circuitry is working.
                        Attached Files

                        Comment


                          #52
                          Re: Vizio VW37 Power Supply PSON working but no 12v or 24v output

                          No, it doesn't make sense that a circuit like that would be isolated. The input comes through the ferrite bead L16.
                          Last edited by tom66; 01-11-2012, 02:02 AM.
                          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.

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                            #53
                            Re: Vizio VW37 Power Supply PSON working but no 12v or 24v output

                            I measured the voltage at the right side of L16 on the through hole via. It settled to 1.095V after about twenty seconds, but initially it was higher. This makes me feel like it is a capacitor issue.

                            Is there any way to find out where the voltage to L16 is coming from? The flow chart says if U6 is not working to check F2 and U1. Does this mean that F2 and U1 are the only two things between U6 and the working standby 5V supply from the connector? Or can there be many things, and the Fuse 2 and U1 are just the most likely to break?

                            Comment


                              #54
                              Re: Vizio VW37 Power Supply PSON working but no 12v or 24v output

                              Originally posted by Tetranitrate View Post
                              This makes me feel like it is a capacitor issue.
                              Your Fluke 117 can measure capacitance. It won't measure ESR, but at least you can check capacitance.

                              Does this mean that F2 and U1 are the only two things between U6 and the working standby 5V supply from the connector?
                              For things like this, I usually "ohms" it out using the continuity beeper to see what is connected.
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                                #55
                                Re: Vizio VW37 Power Supply PSON working but no 12v or 24v output

                                Is this with a good 12/24V going to the main board?

                                It doesn't sound like a cap issue. First off, your power supply board is full of high quality capacitors and it's made by Delta, those things are very nice (and honestly, it's very surprising Vizio decided to use a Delta supply, given the expense.) Secondly, bad caps cause low voltages - but not *very* low - just too low for proper operation - or they cause power supply instability.

                                I would check for open fuses, open diodes, or other components in the power path. Use your multimeter to trace where the power to that inductor comes from (continuity mode is particularly helpful here.)
                                Last edited by tom66; 01-11-2012, 06:30 PM.
                                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.

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                                  #56
                                  Re: Vizio VW37 Power Supply PSON working but no 12v or 24v output

                                  To measure capacitance will I have to remove each individual cap from the board? Or will it be enough to measure them in-circuit, and do any parallel/series calculations for multiple capacitors by hand?

                                  If I have to remove them from the board, shouldn't it be done only after I am a more certain where the faulty capacitor may be located?

                                  Is this with a good 12/24V going to the main board?
                                  No, I learned that I can externally force the PSON high with a pair of AA batteries, and that will cause a steady supply of 12V to turn on and go to the main board as well as turning on the 24V which goes to the inverters. So it doesn't seem like the problem is with the power supply, it seems like it is with a capacitor somewhere on the mainboard. All the electrolytic capacitors on the mainboard are made by Taicon.

                                  I know that the input voltage on the right side of L16 needs to be at least 2 volts (required to turn the U6 chip on), but I don't know how much larger it is supposed to be. If it only has to be around say 3 volts, then it being low at 1.095 could indicate a cap issue somewhere right?

                                  Use your multimeter to trace where the power to that inductor comes from
                                  Inductor L16? Are there any good techniques for measuring continuity between PCB vias? Apart from the flow chart hinting at where L16 could be connected, is there any other way to get an idea of where internal traces may go? Do the dimples on the surface of the PCB indicate anything? Should I just rapidly sweep/drag the multimeter probe across the board until I hear a beep, and then use that to further "lock-in" on where a connection may be? There are hundreds of these small copper rings on this board, and to begin poking at them "blindly" seems kinda daunting.

                                  Comment


                                    #57
                                    Re: Vizio VW37 Power Supply PSON working but no 12v or 24v output

                                    Ok, boom. I did some quick testing for continuity for the input to L16 (the input voltage for U6), and quickly found out why it wasn't working.

                                    It is connected to pins 2,3,4, and 5 of J1. These pins are where the mainboard receives the 12V from the power board - when the power board is working correctly. My problems with U6 are therefore just another symptom of the power supply not turning on because the PSON voltage is not high enough.

                                    Unfortunately this puts me back at square one for identifying the problem. My PSON is low, and I don't know why.

                                    Comment


                                      #58
                                      Re: Vizio VW37 Power Supply PSON working but no 12v or 24v output

                                      Originally posted by Tetranitrate View Post
                                      Ok, boom. I did some quick testing for continuity for the input to L16 (the input voltage for U6), and quickly found out why it wasn't working.

                                      It is connected to pins 2,3,4, and 5 of J1. These pins are where the mainboard receives the 12V from the power board - when the power board is working correctly. My problems with U6 are therefore just another symptom of the power supply not turning on because the PSON voltage is not high enough.

                                      Unfortunately this puts me back at square one for identifying the problem. My PSON is low, and I don't know why.
                                      This is what I expected. The problem is the main board isn't turning on the rails, so you should look for where the standby power goes. What is the standby voltage? Is it stable? Do you get this voltage on any LDOs?
                                      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.

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                                        #59
                                        Re: Vizio VW37 Power Supply PSON working but no 12v or 24v output

                                        I get the correct standby voltage is correct on all the LDOs. The only symptom of something being wrong is the PSON voltage being low at 3.167V instead of 3.3V. This difference is enough to cause an issue.

                                        Unfortunately the service manual flow chart does not provide any help for this particular issue.

                                        Comment


                                          #60
                                          Re: Vizio VW37 Power Supply PSON working but no 12v or 24v output

                                          Originally posted by Tetranitrate View Post
                                          I get the correct standby voltage is correct on all the LDOs. The only symptom of something being wrong is the PSON voltage being low at 3.167V instead of 3.3V. This difference is enough to cause an issue.

                                          Unfortunately the service manual flow chart does not provide any help for this particular issue.
                                          Are there any buck converters on the board that might get the 5V standby? Also, check the bottom of the board for LDOs.
                                          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.

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