AOC v173

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  • Nocta
    Senior Member
    • Mar 2012
    • 117
    • Argentina

    #1

    AOC v173

    Hi guys,

    I bought this computer display. It was not working but I can't find why it's not working. I don't even get a blue/orange light.

    Fuse is OK, it reads 1,2 ohms. I fully recapped the power board. Voltages on the cable that goes to the logic board seem to be OK and stable. I resoldered the whole board just in case.

    I took the mosfet out of the board. It has written "A 2761I 826390". I tested it and I got no resistance or continuity, doesn't matter where I put the probes.

    Any ideas?

    Thanks!
    Attached Files
  • retiredcaps
    Badcaps Legend
    • Apr 2010
    • 9271

    #2
    Re: AOC v173

    Originally posted by Nocta
    I don't even get a blue/orange light.
    If the power board voltages are okay, then a no power LED suggests something wrong with the main board.

    There is one voltage regulator that I can see right by the connector cable.

    What is the part number and voltages on each pin wrt to ground?
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    Comment

    • Nocta
      Senior Member
      • Mar 2012
      • 117
      • Argentina

      #3
      Re: AOC v173

      It's a classic AS1117L-3.3
      Attached Files

      Comment

      • retiredcaps
        Badcaps Legend
        • Apr 2010
        • 9271

        #4
        Re: AOC v173

        At 3.22, it is 2.42% out.

        (3.3 - 3.22)/3.3 = 2.42%

        I use a 1% tolerance rule because that is what I learned from PlainBill. Others like budm use a bigger number like 2-3%. Datasheets also vary in the degree of tolerance.

        So I would say that voltage regulator is in the "gray" area. If this were my monitor, I would replace it using the 1% rule.

        I fixed an Acer 1716 that had an "obviously" bad regulator because the 1117-18 measured 1.6V (or 11% out).
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        Comment

        • retiredcaps
          Badcaps Legend
          • Apr 2010
          • 9271

          #5
          Re: AOC v173

          I should also point out it also depends on the accuracy of your multimeter. A multimeter that is +/- 1% DC V accuracy may give a false reading if it is out of calibration.

          Also, a low battery will give false readings. Not all multimeters are very good at displaying low battery when they should and give inaccurate readings.
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          Comment

          • Nocta
            Senior Member
            • Mar 2012
            • 117
            • Argentina

            #6
            Re: AOC v173

            Hmmm I see your point but there's a "big" difference between 1.6 and 3.22v. Do you think it's enough for not even lighting up a led?

            I think I've a couple of AS1117L-3.3 here. I'll update you if I've any news.

            I replaced the battery of my multimeter a couple of months ago. It don't use it every day and usually for simple things like reading voltages, low resistances ... I'll see if I have a new battery and replace it. Just to be sure

            Comment

            • Nocta
              Senior Member
              • Mar 2012
              • 117
              • Argentina

              #7
              Re: AOC v173

              Alright, so I changed the voltage regulator. Now the output voltage is 3.28v but no blue/orange light is on :/

              Comment

              • Rtech
                Badcaps Legend
                • Jul 2010
                • 1095

                #8
                Re: AOC v173

                Have you got voltage and Ground going to the control board, where the on/off switch is etc ??,and if so is that onto the on/off switch and does the switch operate correctly.

                Comment

                • selldoor
                  Slow Learner
                  • Dec 2010
                  • 7870

                  #9
                  Re: AOC v173

                  Can we assume you replaced the mosfet with a working one - did you test it prior to replacement.


                  With it all connected up what voltages to you get at the connectors.
                  There is a small startup cap perhaps 50v47u on the primary side perhaps the one next to D804 - if it has gone bad the other voltages will not start.

                  Have you tested U 501 and U502
                  Last edited by selldoor; 08-19-2012, 02:22 AM.
                  Please upload pictures using attachment function when ask for help on the repair
                  http://www.badcaps.net/forum/showthread.php?t=39740

                  Comment

                  • retiredcaps
                    Badcaps Legend
                    • Apr 2010
                    • 9271

                    #10
                    Re: AOC v173

                    Originally posted by Nocta
                    Hmmm I see your point but there's a "big" difference between 1.6 and 3.22v.
                    You missed a key part of my post. It was a 1117-18 regulator which means the output should be 1.8V.
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                    Comment

                    • Nocta
                      Senior Member
                      • Mar 2012
                      • 117
                      • Argentina

                      #11
                      Re: AOC v173

                      Originally posted by Rtech
                      Have you got voltage and Ground going to the control board, where the on/off switch is etc ??,and if so is that onto the on/off switch and does the switch operate correctly.
                      I guess the control board is working. The resistances there have voltage (don't remember the exact number).

                      Originally posted by selldoor
                      Can we assume you replaced the mosfet with a working one - did you test it prior to replacement.


                      With it all connected up what voltages to you get at the connectors.
                      There is a small startup cap perhaps 50v47u on the primary side perhaps the one next to D804 - if it has gone bad the other voltages will not start.

                      Have you tested U 501 and U502
                      I think the mosfet is working. Like I said, it doesn't read any resistance. I tested it even out of the board.

                      I'll check the cap you said but I replaced all of them. There's one next to the mosfet 10uFx25v. I'll check U501 and U502 too.

                      Originally posted by retiredcaps
                      You missed a key part of my post. It was a 1117-18 regulator which means the output should be 1.8V.
                      Yes, you're right but I realized after I posted :P

                      Comment

                      • Nocta
                        Senior Member
                        • Mar 2012
                        • 117
                        • Argentina

                        #12
                        Re: AOC v173

                        Ok, so I tested U501 and U502. Both of them have written on it "9962GH 822116".

                        U502, pin 2 (middle): 14,7v
                        The rest pins read 0v.

                        I attached a picture.

                        Also, I tested what I think it's a fuse. It has continuity but I don't know if it's really a fuse.

                        I don't have other control board to test but if I disconnect it, I get 0v on the cable connected to the logic board.
                        Attached Files
                        Last edited by Nocta; 08-21-2012, 10:25 AM.

                        Comment

                        • retiredcaps
                          Badcaps Legend
                          • Apr 2010
                          • 9271

                          #13
                          Re: AOC v173

                          Originally posted by Nocta
                          Also, I tested what I think it's a fuse. It has continuity but I don't know if it's really a fuse.
                          It looks like a SMD fuse. It has the 4A 32V F pcb designator so it is a fuse.
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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

                          • selldoor
                            Slow Learner
                            • Dec 2010
                            • 7870

                            #14
                            Re: AOC v173

                            Yes its a fuse, not seen a fuse up there before anyway you say it tests good.
                            I have been looking for the datasheet for the U501/2
                            Attached Files
                            Please upload pictures using attachment function when ask for help on the repair
                            http://www.badcaps.net/forum/showthread.php?t=39740

                            Comment

                            • Nocta
                              Senior Member
                              • Mar 2012
                              • 117
                              • Argentina

                              #15
                              Re: AOC v173

                              Great. I couldn't even find the datasheet.

                              So guys, what do you think? U501 and U502 are shorted or it must be something else?

                              Comment

                              • budm
                                Badcaps Legend
                                • Feb 2010
                                • 40746
                                • USA

                                #16
                                Re: AOC v173

                                The problem with no indicator light is the main baord not functioning, the shorted MOSEFTs would cause the power supply to stay in shutdown mode which will kill the power to the logic board, but you have indicated that the voltage is OK, then "So guys, what do you think? U501 and U502 are shorted or it must be something else?" are you saying the MOSFET's tested shorted?
                                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

                                • Nocta
                                  Senior Member
                                  • Mar 2012
                                  • 117
                                  • Argentina

                                  #17
                                  Re: AOC v173

                                  MOSFET seems OK to me. It doesn't read less than 30ohms doesn't matter how. For what I have learned here, a shorted mosfet should read less than 30 ohms.

                                  Comment

                                  • budm
                                    Badcaps Legend
                                    • Feb 2010
                                    • 40746
                                    • USA

                                    #18
                                    Re: AOC v173

                                    I did not think so that the MOSFET's are bad either since they are connected directly to the B+ for the inverter power supply. Still need to do more testing of the logic board, since the regulator's voltages are OK now, you will need to look and see if the processor is even active, you will need an Oscilloscope to look at the Xtal and clocking signals to see if they are active or not.
                                    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

                                    • Nocta
                                      Senior Member
                                      • Mar 2012
                                      • 117
                                      • Argentina

                                      #19
                                      Re: AOC v173

                                      Well, I don't have an oscilloscope so I guess I've reached my limit ;(

                                      Comment

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