ViewSonic VA903b

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  • 820uF
    Member
    • Apr 2012
    • 39
    • Russia

    #21
    Re: ViewSonic VA903b

    got the same model monitor.
    power button does nothing, no powerup when power cable attached, no caps bubleing.
    transformer seconderies seem to be ok one 789 second 791.
    what could be the problem?

    Comment

    • 820uF
      Member
      • Apr 2012
      • 39
      • Russia

      #22
      Re: ViewSonic VA903b

      hi-res pic of it

      Comment

      • ben7
        Capaholic
        • Jan 2011
        • 4059
        • USA

        #23
        Re: ViewSonic VA903b

        Check the main fuse. If the fuse is good, check the voltage on the biiig black filter capacitor.
        Muh-soggy-knee

        Comment

        • 820uF
          Member
          • Apr 2012
          • 39
          • Russia

          #24
          Re: ViewSonic VA903b

          main fuse is ok.
          The 400V cap you mean while power is connected ?

          Comment

          • Rtech
            Badcaps Legend
            • Jul 2010
            • 1095

            #25
            Re: ViewSonic VA903b

            Yes, measure DC volts with power on ...'BE CAREFUL'.
            At the top of your picture there are 3 diodes,with Power OFF put your meter on Diode Test and measure across each.If you have not got Diode test then put on Resistance.At least one of these tend to go short circuit,which results in no voltage out.

            Comment

            • 820uF
              Member
              • Apr 2012
              • 39
              • Russia

              #26
              Re: ViewSonic VA903b

              318V it shows.
              big yellow transformer makes hearable static.
              can there be soething?
              Last edited by 820uF; 01-20-2013, 07:08 AM.

              Comment

              • selldoor
                Slow Learner
                • Dec 2010
                • 7870

                #27
                Re: ViewSonic VA903b

                318V is OK can you check the volages on the connector to the main board.
                (Black and red wires) You need to have the boards connected and the lights if possible. Set meter on 20 VDC
                Black probe on a ground screw then check each pin on the socket and post the results.

                Did you test the 3 diodes as per Rtechs post no 25
                Please upload pictures using attachment function when ask for help on the repair
                http://www.badcaps.net/forum/showthread.php?t=39740

                Comment

                • 820uF
                  Member
                  • Apr 2012
                  • 39
                  • Russia

                  #28
                  Re: ViewSonic VA903b



                  Measures with beep function:
                  1. 530
                  2. 232
                  3. 232

                  Measures with 2k diod function:
                  1. .629
                  2. .269
                  3. .269




                  Measures between ground screw and these pins:

                  1. 0,01V
                  2. 0.01V
                  3. 5,03V
                  4. 5,03V
                  5. 0,00V
                  6. 0,00V

                  Comment

                  • selldoor
                    Slow Learner
                    • Dec 2010
                    • 7870

                    #29
                    Re: ViewSonic VA903b

                    Ok for diodes you need to measure in both directions

                    Most tests we use are in this guide written by retiredcaps start at post 19
                    https://www.badcaps.net/forum/showthread.php?t=10419

                    On the voltage picture I notice a 24v on the board. If that is a list of what you are supposed to get on that connector, please can you list it.

                    Also if the top one is 24v you need to test it with meter on higher than 20vDC - sorry.


                    I have been reading the rest of this thread. It seems that on your board the 1000uf
                    caps generally fail and they recommend replacing the startup cap which is a small one on the primary side. 50v 10uf
                    Last edited by selldoor; 01-20-2013, 11:58 AM.
                    Please upload pictures using attachment function when ask for help on the repair
                    http://www.badcaps.net/forum/showthread.php?t=39740

                    Comment

                    • 820uF
                      Member
                      • Apr 2012
                      • 39
                      • Russia

                      #30
                      Re: ViewSonic VA903b





                      Measures with 200 ohm function:
                      1. nothing both ways
                      2. 198,0 back on cathode side, second way nothing
                      3. 198,0 back on cathode side, second way nothing

                      I think the markings on PCB belong to another model.
                      Tere is marked 9 pins on PCB but it only has 6


                      replacing that small capiside the corner of that heatsink ?
                      ok i'll try

                      Thanks!

                      Comment

                      • selldoor
                        Slow Learner
                        • Dec 2010
                        • 7870

                        #31
                        Re: ViewSonic VA903b

                        Originally posted by 820uF
                        [
                        Measures with 200 ohm function:
                        1. nothing both ways
                        2. 198,0 back on cathode side, second way nothing
                        3. 198,0 back on cathode side, second way nothing
                        ,

                        As it measured more than 200 previously you need to increase the scale
                        please check them again on 2000.
                        When you say "Nothing" do you mean 0 zero or 1 as in off scale (same as probes apart.)

                        Yes since I asked about the board label I saw it on another picture so we can only guess what we should have.-
                        Hopefully changing the start up cap will help. How a bout the 1000uf you can use a 16v or 25v- I can only see the mains fuse on the board is that the only one?
                        Please upload pictures using attachment function when ask for help on the repair
                        http://www.badcaps.net/forum/showthread.php?t=39740

                        Comment

                        • 820uF
                          Member
                          • Apr 2012
                          • 39
                          • Russia

                          #32
                          Re: ViewSonic VA903b

                          i ment 1 - off the scale

                          Measures with 2k ohm function:
                          1. .625 back on cathode side, second way off scale (on 20k function it shows 7,53)
                          2. .267 back on cathode side, second way it shows 1,639
                          3. .267 back on cathode side, second way it shows 1,635

                          Changeing that 50v 10uf cap didn't do much


                          Only raised voltage 5,03V to 5,04V

                          Comment

                          • Rtech
                            Badcaps Legend
                            • Jul 2010
                            • 1095

                            #33
                            Re: ViewSonic VA903b

                            Your Post 28 shows:-
                            1. 0,01V
                            2. 0.01V
                            3. 5,03V
                            4. 5,03V
                            5. 0,00V
                            6. 0,00V
                            which actually can be confusing as it looks as your numbering is not corect based on the Legend showing the voltages expected.Your pin 1 is actually pin 3,your pin 2 is 4 etc etc,So what you have got is
                            Adj.....0.1 v
                            On/Off..0.1v
                            5v..5v
                            5v..5v
                            Gnd..0v
                            Gnd..0v
                            So does the 5v vary when everything is plugged in and switched on, with an input signal ?? Have you changed the 1000uf capacitor ?? do you get a voltage on the on/off pin when you initally switch on ??
                            Last edited by Rtech; 01-21-2013, 01:29 AM.

                            Comment

                            • 820uF
                              Member
                              • Apr 2012
                              • 39
                              • Russia

                              #34
                              Re: ViewSonic VA903b

                              5v pins are soldered togeter on the other side. the do not vary.

                              Replaced 16V 1000uf with new one - still all same
                              tried 25v 1000uf cap (as one did here) - still same.

                              Comment

                              • selldoor
                                Slow Learner
                                • Dec 2010
                                • 7870

                                #35
                                Re: ViewSonic VA903b

                                Ok Can you disconnect the main board and with the lights plugged in and the board
                                plugged into the mains can you apply 3 volts to the on/off pin. Use 2x 1.5v batteries.
                                negative to a ground pin. Or if you have a 10k resistor connect the 5v to the on/off pin.

                                We are also going to need pictures of the Main Board - can you post them
                                (max resolution 2000x2000 and 2MB) using the manage attachments button, which is found by clicking "go advanced" under quick reply.

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

                                Examples of what is needed

                                https://www.badcaps.net/forum/attach...7&d=1280167246

                                https://www.badcaps.net/forum/attach...6&d=1280167246

                                https://www.badcaps.net/forum/attach...4&d=1280167246
                                Last edited by selldoor; 01-21-2013, 02:03 PM.
                                Please upload pictures using attachment function when ask for help on the repair
                                http://www.badcaps.net/forum/showthread.php?t=39740

                                Comment

                                • 820uF
                                  Member
                                  • Apr 2012
                                  • 39
                                  • Russia

                                  #36
                                  Re: ViewSonic VA903b

                                  Used some not so full 1,5 batteries on on/off pin. Got 2,7V outof these.
                                  It powered up the LCD - all pixels white.

                                  Here's some pictures:
                                  Attached Files

                                  Comment

                                  • budm
                                    Badcaps Legend
                                    • Feb 2010
                                    • 40746
                                    • USA

                                    #37
                                    Re: ViewSonic VA903b

                                    If the backlights stay on without going black using external force on power source, then your power supply/inverter board is OK. The screen is showing white due to the main board is not getting the power. Now you will have totroubleshoot the main board.
                                    Last edited by budm; 01-24-2013, 11:16 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

                                    • selldoor
                                      Slow Learner
                                      • Dec 2010
                                      • 7870

                                      #38
                                      Re: ViewSonic VA903b

                                      I hate it when we get it down to the mainboard - it does not seem that we get them fixed very often.

                                      Start with testing the voltage regulators - think I see two but look for more.
                                      One is at U3 and one at U7.

                                      Retiredcaps has prepared a guide on how to find ,test and post results.
                                      https://www.badcaps.net/forum/showthread.php?p=261329
                                      Please upload pictures using attachment function when ask for help on the repair
                                      http://www.badcaps.net/forum/showthread.php?t=39740

                                      Comment

                                      • budm
                                        Badcaps Legend
                                        • Feb 2010
                                        • 40746
                                        • USA

                                        #39
                                        Re: ViewSonic VA903b

                                        Here is the service manual.
                                        Attached Files
                                        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

                                        • 820uF
                                          Member
                                          • Apr 2012
                                          • 39
                                          • Russia

                                          #40
                                          Re: ViewSonic VA903b

                                          U3
                                          1. 5.04v
                                          2. 3,30v
                                          3. 0,00v - is this normal ?
                                          4. 3,30v

                                          U7
                                          1. 3,30v
                                          2. 1,80v
                                          3. 0,00v
                                          4. 1,80v

                                          U4
                                          1. 3,20v
                                          2. 3,20v
                                          3. 3,23v
                                          4. 0,00v
                                          5. 0,00v
                                          6. 0,00v
                                          7. 0,00v
                                          8. 0,00v
                                          Attached Files

                                          Comment

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