Viewsonic VT2430 fluctuating 5V rail

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  • rddube
    Aspiring Expert
    • Jun 2013
    • 908
    • Canada

    #1

    Viewsonic VT2430 fluctuating 5V rail

    Hello to everyone,

    I need some help with this tv/monitor. All is working well, except that I noticed the power indicator light (blue) was fluctuating while using it.

    I opened her up and I have all my voltages +5V, 12V etc, rock solid when the monitor is in standby mode. When I power it up, it comes on fine but the 5V rail is fluctuating from 4.8V to 5.1V constantly which is causing the indicator light to fluctuate (throb).

    I checked all the caps on the power supply board and they are all good (including ESR and value), even the big guy! I checked resistors, diodes and a bunch of components, but everything seems fine.

    So when there is no load on the power supply all is fine. As soon as there is some drain, the 5V rail fluctuates from 4.8V to 5.1V constantly like a heartbeat, which I think is out of range...but the monitor/tv works fine. Any ideas what it could be?

    I am attaching photos with the service manual and the schematics - I just can't figure it out and need help from the masters!

    Thank you!

    Ray
    Attached Files
    Last edited by rddube; 07-20-2018, 11:20 AM.
  • budm
    Badcaps Legend
    • Feb 2010
    • 40746
    • USA

    #2
    Re: Viewsonic VT2430 fluctuating 5V rail

    Are the 12V, 19V steady? 5V, 12V, and 19V are generated by the same transformer.
    The feedback for the output Voltage monitor all 3 power supplies outputs so I expect the other two outputs to fluctuate also.
    Last edited by budm; 07-20-2018, 12:05 PM.
    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

    Comment

    • R_J
      Badcaps Legend
      • Jun 2012
      • 9532
      • Canada

      #3
      Re: Viewsonic VT2430 fluctuating 5V rail

      The first cap. I would replace would be C810 10µf/50v

      Comment

      • rddube
        Aspiring Expert
        • Jun 2013
        • 908
        • Canada

        #4
        Re: Viewsonic VT2430 fluctuating 5V rail

        Thank you Budm and R_J for stepping in!

        Budm: the 12V fluctuates for 11.75V to 12.5V (when load is on) but not in standby. I can't find a 19V??

        R_J: C810 on board is a 22uf 50V which I took out and measured with my ESR meter and it looks fine. But you are right, the schematics calls for a 10uf, so I don't know if that could be the cause or not?

        I did measure the voltage on the big cap, and I do get a fluctuation there: 160V steady on standby, when power up, fluctuates from 148V to 152V ???.is that normal?
        Last edited by rddube; 07-20-2018, 12:40 PM.

        Comment

        • R_J
          Badcaps Legend
          • Jun 2012
          • 9532
          • Canada

          #5
          Re: Viewsonic VT2430 fluctuating 5V rail

          If C810 is a 22µf then I would leave it, schematic could be different. any small change of voltage on the large cap won't have any effect on the output,
          The led is supplied by the VCC5V-ST, there is a 1500µf/16v (C110) on the main board that should take care of any voltage fluctuation, unless it's bad?
          Last edited by R_J; 07-20-2018, 03:12 PM.

          Comment

          • rddube
            Aspiring Expert
            • Jun 2013
            • 908
            • Canada

            #6
            Re: Viewsonic VT2430 fluctuating 5V rail

            Ok R_J will check C110 and report back...thanks again!
            Last edited by rddube; 07-20-2018, 05:22 PM.

            Comment

            • rddube
              Aspiring Expert
              • Jun 2013
              • 908
              • Canada

              #7
              Re: Viewsonic VT2430 fluctuating 5V rail

              Ok, so I took out C110 and it gives me 1285uf with ESR of 1.2. So I decided to take out C101 and C108 which are same value, and got C101 1356uf ESR .03 and C108 1555uf and ESR 0.

              So I guess you're right on R_J, I should change C110 and C101, right? Will try to find a replacement tomorrow and report back with the new capacitors.

              Comment

              • rddube
                Aspiring Expert
                • Jun 2013
                • 908
                • Canada

                #8
                Re: Viewsonic VT2430 fluctuating 5V rail

                Replaced C110, C101 and C108 with 1500uf low ESR Panasonic caps. And now, I have no power??

                Measured my voltages at p101 and 13V is down to 6-7V, no 5V. So I disconnected the main board from the power board and got back 13V steady, 5V fluctuating.

                Rechecked my soldering on the new caps, redid them, but same result. Now I am really lost Help!

                Comment

                • R_J
                  Badcaps Legend
                  • Jun 2012
                  • 9532
                  • Canada

                  #9
                  Re: Viewsonic VT2430 fluctuating 5V rail

                  It could be that you power supply can't supply the current required, do you have around a 10ohm 2watt resistor, place it across the 5 volt line (plug disconnected from main) that should draw around 500ma, if it can't supply that then fault is with power supply.
                  Simply replacing the caps should not have caused that problem. but being new caps the extra load might be enough to effect the 5 volts, and the 5 volts controls the feedback so if goes low so do the other voltages.
                  You could have a poor D822 diode, going open under load
                  Last edited by R_J; 07-21-2018, 12:04 PM.

                  Comment

                  • RepairMonkey
                    New Member
                    • Jul 2018
                    • 3
                    • UK

                    #10
                    Re: Viewsonic VT2430 fluctuating 5V rail

                    Originally posted by rddube
                    Replaced C110, C101 and C108 with 1500uf low ESR Panasonic caps. And now, I have no power??

                    Measured my voltages at p101 and 13V is down to 6-7V, no 5V. So I disconnected the main board from the power board and got back 13V steady, 5V fluctuating.

                    Rechecked my soldering on the new caps, redid them, but same result. Now I am really lost Help!
                    I'm assuming Electrolytic caps - is the polarity correct?

                    Comment

                    • rddube
                      Aspiring Expert
                      • Jun 2013
                      • 908
                      • Canada

                      #11
                      Re: Viewsonic VT2430 fluctuating 5V rail

                      Thanks R_J for your patience! I removed the caps (the low ESR Panasonice 1500uf 16v) and reinstalled them, and now everything is back to normal, so monitor/tv fires up and 5V still strobing.

                      I will try the test you suggest with a 2 watt 10ohm resistor - so I plug this resistor on the 5V line and ground (without being connected to main) and what should I do after that, measure the 5v line?

                      I'll also check the D822 diode out of circuit and report back. Thanks again!!

                      Comment

                      • R_J
                        Badcaps Legend
                        • Jun 2012
                        • 9532
                        • Canada

                        #12
                        Re: Viewsonic VT2430 fluctuating 5V rail

                        Yes to checking the 5 volt line, I choose a 10 ohm as that would draw 500ma, the supply should at least do that, if the 5 volt line drops with that resistor then the power supply has an issue.
                        I would think it should do 1 amp so you could use a lower value higher wattage resistor, 5 volts, 5 ohm = 1 amp of current,
                        Checking the diode will likely not tell you much, it will likely check ok.
                        Now that I look closer I see it is a dual diode so it should be ok

                        Comment

                        • rddube
                          Aspiring Expert
                          • Jun 2013
                          • 908
                          • Canada

                          #13
                          Re: Viewsonic VT2430 fluctuating 5V rail

                          Ok, so what should I do?

                          Comment

                          • R_J
                            Badcaps Legend
                            • Jun 2012
                            • 9532
                            • Canada

                            #14
                            Re: Viewsonic VT2430 fluctuating 5V rail

                            I was giving a suggestion on how to check the 5volt standby of the power supply, by providing a load other than the main board. If you don't have a resistor to load the 5 volts I can only assume the main board is ok and the fault is with the power supply not providing enough current.
                            Did you check C827? I see from your picture it is a smd cap.
                            This could be hard to troubleshoot since it is working just not supplying enough current.
                            I see you checked the caps like c833,c824 but have you tried replacing them to see if that stabalizes the +5
                            Last edited by R_J; 07-21-2018, 09:13 PM.

                            Comment

                            • rddube
                              Aspiring Expert
                              • Jun 2013
                              • 908
                              • Canada

                              #15
                              Re: Viewsonic VT2430 fluctuating 5V rail

                              Hello R_J,

                              I tried with a 10ohm resistor on all 3 lines of 5V and it is rock steady at 5.03V. So I tried what you suggested a 5 ohm resistor to get a bit more load, and all 3 lines of 5V are rock steady at 5.01V. So I guess the problem is not with the power supply, right?

                              What else?

                              Comment

                              • rddube
                                Aspiring Expert
                                • Jun 2013
                                • 908
                                • Canada

                                #16
                                Re: Viewsonic VT2430 fluctuating 5V rail

                                I should mention that when it is powered on and the blue Led (it is blue when powered on and amber when powered off and in standby), I can hear a faint throb through the speakers of the monitor/tv. It doesn't change if I increase volume, it remains faint. Not sure if that can give a clue?

                                Comment

                                • R_J
                                  Badcaps Legend
                                  • Jun 2012
                                  • 9532
                                  • Canada

                                  #17
                                  Re: Viewsonic VT2430 fluctuating 5V rail

                                  Have you checked if the sound is ok? it could be a fault with the audio amp ic. If you play music and turn up the volume how does that effect the blue led.
                                  Last edited by R_J; 07-22-2018, 11:21 AM.

                                  Comment

                                  • rddube
                                    Aspiring Expert
                                    • Jun 2013
                                    • 908
                                    • Canada

                                    #18
                                    Re: Viewsonic VT2430 fluctuating 5V rail

                                    Ok, I checked the sound and it is fine, in fact very good. Do you think it could be some of the capacitors on the main board, there are quite a few, especially the 10uf 16v, there are tons of them but none of the caps are bulged or anything.

                                    Really don't know what to look at next. Tks R_J

                                    Comment

                                    • rddube
                                      Aspiring Expert
                                      • Jun 2013
                                      • 908
                                      • Canada

                                      #19
                                      Re: Viewsonic VT2430 fluctuating 5V rail

                                      So I decided to do a temp test with an infrared thermometer on the main board, wanting to see if some caps might heat up....didn't find any that looked abnormal.

                                      However in the EEprom section, I did find the resistors around the EEProm to be heating quite a bit (some of them), one of them R338 100R went up to 77C, still climbing slowly. So I decided to check their values and found 3 that don't correspond to the schematic. R336, should be 4.7K is at 2.4K, R287 should be 4.7K is at 3.9K and R310 should be 4.7K is at 4.2K. I know this section runs on 3.3V but maybe it might affect the 5V rail, what do you think?

                                      Finally, on all capacitors the only one that seems to heat up a bit more than the others is C259 220uf 16V.

                                      Comment

                                      • R_J
                                        Badcaps Legend
                                        • Jun 2012
                                        • 9532
                                        • Canada

                                        #20
                                        Re: Viewsonic VT2430 fluctuating 5V rail

                                        Those resistors were likely changed during a board revision, they are pullup resistors on clock and data lines, not likely to effect the problem.
                                        C259 is panel-vcc filter, turn off tv, then unplug the lvds cable from the panel, turn on tv, do you still here the throb in the speakers?

                                        Comment

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