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Viewsonic VG920 No HV for the tubes

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    #1

    Viewsonic VG920 No HV for the tubes

    I have a (VS10790) with a PSU (part# 715G1492-1). I scanned the three posts here for this monitor and not much matches my problem. I used the other posts and found voltage info, but still no joy.
    I replaced ten caps on the PSU purchased from LCDAlternatives and still no joy.
    The problem is:
    I have AC power, and a power LED when the switch is pressed. The display fires for a split second and then off. The power LED stay green. It will go to amber when the computer goes to standby. It appears the HV to the tubes is shutting down, but all other power remains.
    Once in a while the display works, the HV stays up and the image is great as long as it is not powered down or goes into standby from the computer. Thanks in advance for any help.
    Tags: None
    #2
    Re: Viewsonic VG920 No HV for the tubes

    Hi lee welcome to the forum.

    Have you tested your inverter transformer? This can cause the monitor to shut its self off if shorted.

    Can u remember the make of he caps that you put into your monitor? Did you match the values of the ones that you took out exactly?

    Can we have some pics of the top and bottom of both boards so that we can help advise you further?
    Fixed so far : 1 Home cinema system, 16 LCD Monitors, 4 LCD TV's

    How to resize your pictures guide click HERE
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      #3
      Re: Viewsonic VG920 No HV for the tubes

      Thanks for your reply. No I have not tested the transformers, yes there are two. I don't think it's the transformers as all the tubes shut down at the same time. Let me know if my assumption is correct. But please let me know how to test them other than with my ohmmeter.
      The replacement caps, ten of them came from LCDAlternatives and are as good or better than the originals. The new ones are high temp and low tolerance.
      The photos of the PSU upper sides were take before the caps were replaced. All electrolytic caps except the large 100mf 450v by the FW bridge were replaced. It has nothing to do with the HV.
      Photos attached are the PSU and the output/interface board. I did not photo the audio board.
      Thank you in advance for any help.
      Attached Files
      Last edited by Lee General; 04-25-2012, 09:09 AM.

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        #4
        Re: Viewsonic VG920 No HV for the tubes

        Whats written on IC901 on the bottom of the power board?
        Fixed so far : 1 Home cinema system, 16 LCD Monitors, 4 LCD TV's

        How to resize your pictures guide click HERE
        Retiredcaps Ideal post example click HERE

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          #5
          Re: Viewsonic VG920 No HV for the tubes

          IC901 reads:
          203D6
          PGGN

          Comment

            #6
            Re: Viewsonic VG920 No HV for the tubes

            Please notes that:
            All the lamps and the inverter circuits will be shutdown if the Inverter circuits (control by the inverter driver IC)
            1) Detect open lamp connection (if any one of the lamps does not conduct within about 1.5 seconds after the the strike voltage is applied).

            2) Shorted winding on any one of the transformers.

            3) Too much current draw by the lamp.

            4) Bad MOSFET's transformer drivers.

            5) Bad connections on the lamps, in the inverter circuits.

            So there can be many possibilties that any of the above can cause the lamps to shutdown. Testing the inverter circuits with known good lamp will be one way to narrow down the problem.
            Beside Ohming out the transformers, you should remove that blue cap on the middle of the board (sitting close to the transformers and the two MOSFET's, check the value and the resistance leakage of that cap.
            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

              #7
              Re: Viewsonic VG920 No HV for the tubes

              The blue cap has been on my list but have not taken the time to find a replacement. I'll check leakage ASAP. It is .33mf 250v. I have the four, also blue 12pf 3kv by the transformers on the way. Someone, Scott at LCDAlternatives suggested them.
              FYI: IC U406 on the output/interface board had already been removed when I got the monitor. I looked for it as per a post or two in this forum to remove/replace it to solve similar problems. Post #8250 I believe.

              Comment

                #8
                Re: Viewsonic VG920 No HV for the tubes

                I would just check for the value and the leakage resistant, it is the DC blocker for the inverter transformer drive circuits.
                You may waht to try this to see if it is the inverter or the lamp problem:
                https://www.badcaps.net/forum/showthread.php?t=19987
                Last edited by budm; 04-25-2012, 11:38 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

                Comment

                  #9
                  Re: Viewsonic VG920 No HV for the tubes

                  Thanks. On my list. I have a few things to check and test thanks to you folks.

                  Comment

                    #10
                    Re: Viewsonic VG920 No HV for the tubes

                    Details at post #19 and #20

                    https://www.badcaps.net/forum/showthread.php?t=10419
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                    We respectfully ask that you make some time and effort to read some of the guides available for basic troubleshooting. After you have read through them, then ask clarification questions or report your findings.

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                      #11
                      Re: Viewsonic VG920 No HV for the tubes

                      I have good news. I used the info from budm to check if the problem was the inverter or tubes. After I cut open a 13w CFL I remembered I had two pair of tubes from a throwaway monitor. Shorter but unbroken. I plugged them in and they lit and stayed lit as long as there was signal from a computer. They cycled on and off when the computer told the display to go into standby. What a great idea with the CFL! I appreciate the chance to learn and learn I did.
                      Then I tried the original tube sets and they still went off after a split second. I took them out of the display and one tube was cracked. It would appear it made a short and forced the PSU to shutdown as a protection. Yea!
                      So the need now is for a tube set. I researched the inet and I'm not having great success. Any ideas or companies that can supply the replacement assembly? I would like to purchase the whole assembly if possible.
                      Thank you all for all your timely and factual help. I have fixed several monitors by reading this forum, but this was the first time I had to post a problem. It was a great experience.

                      Comment

                        #12
                        Re: Viewsonic VG920 No HV for the tubes

                        Originally posted by Lee General View Post
                        Any ideas or companies that can supply the replacement assembly? I would like to purchase the whole assembly if possible.
                        Members have good feedback for ccflwarehouse.com. They sell preassembled/preharnessed assemblies.

                        http://www.ccflwarehouse.com/harnessedlamps.html

                        Preharnessed will obviously cost more than "bare" lamps.

                        ccfldirect.com is another alternative.
                        --- begin sig file ---

                        If you are new to this forum, we can help a lot more if you please post clear focused pictures (max resolution 2000x2000 and 2MB) of your boards using the manage attachments button so they are hosted here. Information and picture clarity compositions should look like this post.

                        We respectfully ask that you make some time and effort to read some of the guides available for basic troubleshooting. After you have read through them, then ask clarification questions or report your findings.

                        Please do not post inline and offsite as they slow down the loading of pages.

                        --- end sig file ---

                        Comment

                          #13
                          Re: Viewsonic VG920 No HV for the tubes

                          Well done getting to the bottom of your issue. Be careful with any broken tubes they are made of very nasty stuff.
                          Fixed so far : 1 Home cinema system, 16 LCD Monitors, 4 LCD TV's

                          How to resize your pictures guide click HERE
                          Retiredcaps Ideal post example click HERE

                          Comment

                            #14
                            Re: Viewsonic VG920 No HV for the tubes

                            ccflwarehouse.com andccfldirect.com were both recommended by a friend today locally. I already ordered 4 tubes from CCFLDirect this afternoon and already was notified they were shipped. Because of my, and I hate to say this, age I will entrust this friend to assemble the tube sets. He has steadier hands and better eyes.
                            I cannot thank you all enough for all your help and input. What a great forum and community.

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