ViewSonic N3251w Doesn't Turn On

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  • Paul678
    Badcaps Veteran
    • Nov 2011
    • 402

    #1

    ViewSonic N3251w Doesn't Turn On

    Ok, got this one for $5, and the PS didn't even have the always on
    +5V. So after searching the web, I found this solution:

    http://www.fixya.com/support/t354648...c_n3250w_power

    So I checked the Q7 and the zener ZD4, and sure enough, they were bad. Replaced them, and I was overjoyed to see the standby, always on +5V present!

    But.....I celebrated too early!! Depressing the front "ON" button
    didn't turn the TV on, and didn't change the color of the front red LED.

    So I checked that the +3.8V at the main board was being shorted to 0 volts
    when I depressed the switch, and it was.

    Then, using this diagnostic chart:

    http://www.eserviceinfo.com/download...01%2032E2.html

    I checked for the 5V=On, 0V=Off enable signal on line 10 of the main
    cable, and all I found was +0.06V, which doesn't move at all when I
    depress the Power button.

    So it looks like the micro-controller on the main board is faulty. The
    board # is JC328AA71UA.

    I doubt I'll find a schematic for this one.

    Do people sometimes get desperate, and just jumper the always-on
    +5V to the enable line, in bad situations like this, so that they at least have a working TV, that has to be turned on and off with an external AC switch?

    I'm starting to get depressed with this one, if I can't even Ebay the main board!!!!!!

  • tom66
    EVs Rule
    • Apr 2011
    • 32560
    • UK

    #2
    Re: ViewSonic N3251w Doesn't Turn On

    It won't usually work. The backlight may fire up and stuff may happen, but the TV will still be in a zombie state and will not fully boot up. I have done it before with a Samsung out of desperation - just saw a bit of noise on the screen because it wasn't initialising the video processor.

    Check all the voltage regulators and switching supplies.
    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

    • Paul678
      Badcaps Veteran
      • Nov 2011
      • 402

      #3
      Re: ViewSonic N3251w Doesn't Turn On

      Originally posted by tom66
      It won't usually work. The backlight may fire up and stuff may happen, but the TV will still be in a zombie state and will not fully boot up. I have done it before with a Samsung out of desperation - just saw a bit of noise on the screen because it wasn't initialising the video processor.

      Check all the voltage regulators and switching supplies.
      You mean the ones on the main board, right? Like perhaps the
      micro-controller is not being turned on, because it's +3.3 volt
      regulator is bad?

      I couldn't find a schematic....

      Comment

      • tom66
        EVs Rule
        • Apr 2011
        • 32560
        • UK

        #4
        Re: ViewSonic N3251w Doesn't Turn On

        All regulators. Check them all.
        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

        • Paul678
          Badcaps Veteran
          • Nov 2011
          • 402

          #5
          Re: ViewSonic N3251w Doesn't Turn On

          Originally posted by tom66
          All regulators. Check them all.
          Ok, I found the schematic for the main board here:

          http://www.scribd.com/doc/72795409/N3251w-1M-SM


          First thing I notice is that the +5V enable line is kept to 0 Volts
          by the micro-controller energizing the base of Q103 on page 68
          via trace UP3_4, so it's clear the problem is not due to the controller not getting proper voltage. The +3.3V and +1.9V regulators close to the
          controller were working fine.

          I also verified this by tracing UP3_4 to test point 1, which was +0.87 Volts
          (bottom of page 70, close to the controller).

          Then I traced the power button to the keypad interface (pg. 91), to trace
          UP3_0, leading to pad A7 of the BGA on page 70. There was a
          test point here, very close to the chip, where I was able toggle
          the +3.8V to 0 Volts using the power button.

          You can see on page 91 that the ON/OFF signal is energized from +5V
          through a 10k resistor, so it's possible the BGA solder has
          failed on pad A7, so that the controller never sees the power button
          toggling. And perhaps it has an internal pull-up resistor, so it always
          remains off.

          What else can I do in this case, besides trying to bake the main
          board in the oven? There's a reset circuit on page 93; is it possible the system can be reset to
          factory default values, and maybe start working?

          I guess I could sell the now-working power supply on Ebay,
          but it doesn't fetch as much as a working main board!!! And the panel would be
          a pain in the ass to ship without cracking!!

          AAAAAAAAARRRRRRRRRRRGGGGG!!!!!!!

          Last edited by Paul678; 09-20-2012, 07:01 PM.

          Comment

          • Paul678
            Badcaps Veteran
            • Nov 2011
            • 402

            #6
            Re: ViewSonic N3251w Doesn't Turn On

            Update: I just tried using my frequency counter, and
            I was NOT able to see a stable 27 MHz around crystal
            X100, close to the microcontroller.

            Maybe the crystal, and therefore the clock, has died?

            Comment

            • tom66
              EVs Rule
              • Apr 2011
              • 32560
              • UK

              #7
              Re: ViewSonic N3251w Doesn't Turn On

              Or, a more likely alternative: Whatever powers the microcontroller has failed, or there is a RESET line for the micro which has failed (common problem with JVC, Sony and Toshiba sets.) Usually a damaged crystal will still oscillate, just at the wrong frequency. I wouldn't rule out a complete failure though, I would just recommend checking other things first.
              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

              • Paul678
                Badcaps Veteran
                • Nov 2011
                • 402

                #8
                Re: ViewSonic N3251w Doesn't Turn On

                Update:

                I got a used main board off Ebay for $32 total, came from a unit with a
                cracked screen. The TV turns on now!

                The VGA input works, as does a DVD into the component
                inputs. I don't have an HDMI device to test that port with.

                But..... When I tried putting my old UHF loop antenna into the
                DTV port, and put it into DTV mode, I was not able to see any
                channels (neither picture nor channel #), and also, the menu wouldn't allow me to get into the DTV section, so I couldn't do an automated channel scan.

                When I put the loop onto the analog TV input, I was able to get
                one station, channel 65, but all others were "no signal".

                I suppose I could still sell this as-is for cheaper, but if
                someone has any ideas, I'm all ears......

                Comment

                • Paul678
                  Badcaps Veteran
                  • Nov 2011
                  • 402

                  #9
                  Re: ViewSonic N3251w Doesn't Turn On

                  Update:

                  Ok, I was able to do an auto channel scan with the
                  analog TV tuner, and I was able to get 4 channels over the
                  air, so the analog section definitely works fine.

                  But, the menu is still not letting me get into the
                  DTV section. When I try to enter that section, the menu
                  mysteriously turns off, and I just have the blank blue screen,
                  and I can't get back into the menu mode for like at least a
                  couple of minutes. Very weird!

                  I should still be able to sell this to some gamer as-is,
                  because I'm pretty sure the HDMI input will work.....

                  Comment

                  • Paul678
                    Badcaps Veteran
                    • Nov 2011
                    • 402

                    #10
                    Re: ViewSonic N3251w Doesn't Turn On

                    Update:

                    There is a procedure in the service manual to re-initialize the EEPROM, which I performed, but still the same problem.

                    Oh well, I think I can still get like $100 for this as a gaming/computer/dvd monitor......

                    Comment

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