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    Dynex DX-LCD32, with no power

    I'm new to this forum, and new to TV repair so bear with me. I've fixed a few with bad caps, but this one is more involved.

    It's a Dynex DX-LCD32. It's not the one with the "-09" either. That one looks different inside. I picked this one up cheap because it doesn't power on. The guy did say that it would work every now and then, but I haven't seen it yet. I plug it in, and get the orange stand-by light. Press power and the light turns to a solid green. No picture or any sounds. To get it back to stand by mode, I have to press power twice, and get orange flashes. It's really quick, and I tried to count. I either got 9 flashes, or a few times it does abut 15, then stays a solid orange.
    I've looked at every capacitor and none are bulging.
    I have a digital multimeter, and am ready to check whatever that you tell me. Keep in mind that I have very little knowlege of electronics but am willing to learn. I've enclosed some photos of the boards.
    Thanks for any help that you guys can give me. I'm not looking to get into the business, just trying to get a decent TV for the garage.
    Michael
    Attached Files

    #2
    Re: Dynex DX-LCD32, with no power

    Are there any markings on the cable going from the PSU to the main board?

    If so, check the voltages on the pins match these markings.

    I notice one Rubycon cap and a few Chemicons - did you replace these or did someone else? (Or are they factory originals?? That would be very surprising...)
    Last edited by tom66; 02-10-2012, 03:04 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.

    Comment


      #3
      Re: Dynex DX-LCD32, with no power

      I did check those voltages on that side of the PSU, and here is what I got:

      Red and Orange both have 13.2v, and were marked 12v on the board. Yellow and Green both have 5.1v and are marked as 5v on the board. The only other marking was what looked like 1 15v. Not sure if that was supposed to be 1v and 15 v, or what. But neither wire had anything. These wires are going to that small rectangle board. There were 3 wires with no markings on the board but had current. White 2.7, Black 4.0, and Brown 3.1. These were going to the main board.
      And all of these readings were with the green power light on.
      I also checked the other output on the PSU and got nothing except .1 on the wire marked dim on the board.

      Comment


        #4
        Re: Dynex DX-LCD32, with no power

        And I haven't replaced anything, and as far as I know neither did the previous owner. He never mentioned it.

        Comment


          #5
          Re: Dynex DX-LCD32, with no power

          The 12V lines measured 13.2V? That's rather high... Something doesn't seem right. Where were you measuring ground?
          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.

          Comment


            #6
            Re: Dynex DX-LCD32, with no power

            At the chassis ground screw.

            Comment


              #7
              Re: Dynex DX-LCD32, with no power

              Even using the wire in that plug that is labeled GND, I still get 13.2 on those wires.

              Comment


                #8
                Re: Dynex DX-LCD32, with no power

                Originally posted by tom66 View Post
                The 12V lines measured 13.2V? That's rather high...
                From the computer lcd monitor world, a lot of the secondary voltages are unregulated and appear high, but then fall into "spec" when everything is working (i.e. there is a proper load).

                It may be the same in the TV world especially since the backlights are not on to draw any load.
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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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                Comment


                  #9
                  Re: Dynex DX-LCD32, with no power

                  That may well be true - although it's not typical for a supply with standby power.

                  Sometimes a higher voltage is indicative of bad caps because the power supply controller is overshooting or is unstable.
                  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.

                  Comment


                    #10
                    Re: Dynex DX-LCD32, with no power

                    Originally posted by tom66 View Post
                    That may well be true - although it's not typical for a supply with standby power.

                    Sometimes a higher voltage is indicative of bad caps because the power supply controller is overshooting or is unstable.
                    I agree with everything you are saying. Just sharing what we have seen in the lcd computer monitor world.
                    --- 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.

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                    Comment


                      #11
                      Re: Dynex DX-LCD32, with no power

                      Originally posted by retiredcaps View Post
                      I agree with everything you are saying. Just sharing what we have seen in the lcd computer monitor world.
                      Yes, I have seen similar situations with computer power supplies, with no load voltages sometimes being quite high, above nominal ratings.

                      In my experience (and that of others on this forum) the #1 failure mode with bad caps is a decrease in output voltages, not an increase, although a capacitor decreasing in capacitance, or one with an extremely high ESR would probably cause an increase in voltage. Effectively, at high frequencies, the cap is supposed to act as a short circuit, to filter out the higher frequencies, but if it doesn't have a low enough ESR, there is no where for this high frequency noise to go, other than to increase the output voltage.
                      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.

                      Comment


                        #12
                        Re: Dynex DX-LCD32, with no power

                        Originally posted by tom66 View Post
                        Effectively, at high frequencies, the cap is supposed to act as a short circuit, to filter out the higher frequencies, but if it doesn't have a low enough ESR, there is no where for this high frequency noise to go, other than to increase the output voltage.
                        Not really because the reference voltage for the ripple's peak-peak is the DC voltage anyway.
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                        Comment


                          #13
                          Re: Dynex DX-LCD32, with no power

                          Ok. So what should I check next, or do I need to replace some capacitors?

                          Comment


                            #14
                            Re: Dynex DX-LCD32, with no power

                            Anyone?

                            Comment


                              #15
                              Re: Dynex DX-LCD32, with no power

                              Still sitting here with an open TV. Can someone help me out please? I'm ready to get this thing fixed.

                              Thank you!

                              Comment


                                #16
                                Re: Dynex DX-LCD32, with no power

                                Can you please take good clear pictures of the the whole chassis so we may be we will be able to see how it is wired up? We also need to see the third connector on the power supply board which I think it goes to the Inverter board, back side pictures of the power supply, closed up pictures of the inverter multi-pin connector, LCD panel make, model, revision number so we can look up the spec of the LCD panel which will show the T-CON and inveter board pin out of the connectors, etc.
                                By the way, do you get sound?, also try turning it on without the inverter board discoonected from the power supply board.
                                Last edited by budm; 03-02-2012, 04:12 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


                                  #17
                                  Re: Dynex DX-LCD32, with no power

                                  Thanks Bud. I'll get working on those pictures and specs tonight when I get home. I appreciate the help.

                                  Comment


                                    #18
                                    Re: Dynex DX-LCD32, with no power

                                    Looking at your picture of the power supply, I think this is what it has on it, see PDF. Right now the standby PS seems to be working (this power supply is running 24/7).
                                    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


                                      #19
                                      Re: Dynex DX-LCD32, with no power

                                      All of your assumptions are correct about where the wires are going. And I checked the voltage on the cap, and they fell right in line with where you said that it would.

                                      Comment


                                        #20
                                        Re: Dynex DX-LCD32, with no power

                                        So if I am right, right now you do not have the 24vdc feeding the Inverter board, yes/no? If not, disconnect the cable to the inverter board an see if the 24vdc comes back since if the 24vdc PS circuits sensing over current draw, it will go into shutdown mode.
                                        Another reason you do have 23vdc can be due to 24vdc circuits itself, or it is not getting the command from the main board to turn it on.
                                        Any voltage labels on the power supply connector at all? That will be a big help if they are labeled.
                                        Last edited by budm; 03-02-2012, 05:11 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

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