flatron L1915s

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  • sabre504
    Badcaps Veteran
    • May 2010
    • 449
    • United Kingdom

    #1

    flatron L1915s

    Hi have this board from a 19" Flatron started out with no power .
    I have changed all the caps for rubycon YXA YXG but am still getting no power output from the CW201 connection that goes to the switchs and logic board .
    Power is going in as far as the main cap showing 339v (UK 240v AC)

    I know the logic board and switchs work as i rigged up a temp power supply and had them working .
    Any suggestions on what to check next as am coming up short or am missing something .

    Thanks in advance for any input
    Attached Files
  • alexanna
    Member
    • Mar 2010
    • 1346

    #2
    Re: flatron L1915s

    Did you also change the small 50v start up caps around the SMPS coil?
    Whatever I do, I consider it a success, if in the end I am breathing, seeing, feeling and hearing!

    Comment

    • sabre504
      Badcaps Veteran
      • May 2010
      • 449
      • United Kingdom

      #3
      Re: flatron L1915s

      Yes changed them all

      Comment

      • alexanna
        Member
        • Mar 2010
        • 1346

        #4
        Re: flatron L1915s

        Do any of the voltages come back with the logic board disconected?
        Whatever I do, I consider it a success, if in the end I am breathing, seeing, feeling and hearing!

        Comment

        • Rtech
          Badcaps Legend
          • Jul 2010
          • 1095

          #5
          Re: flatron L1915s

          PSU/Inverter ONLY,with BLs plugged in,power on,put 3volts Dc into the BL_ON and earth pins,and prove the Power supply is correct,then you can move on from there.

          Comment

          • jetadm123
            Badcaps Legend
            • Feb 2010
            • 2169

            #6
            Re: flatron L1915s

            Sounds like the power supply isn't starting up. Try measuring the VCC of the PWM chip, U101, pin 7. Ground is pin 5. Start voltage for the chip should be approx. 12V. If not, try checking the diode connected to VCC pin for shorts. We know that the startup cap is good, since you changed it. Also check resistor(s) on the VCC line for correct value and check the mosfet, Q101, for shorts.

            Comment

            • sabre504
              Badcaps Veteran
              • May 2010
              • 449
              • United Kingdom

              #7
              Re: flatron L1915s

              NO power whether logic board connected or not ,
              I will check the other suggestions and report back later .

              Thanks

              Comment

              • sabre504
                Badcaps Veteran
                • May 2010
                • 449
                • United Kingdom

                #8
                Re: flatron L1915s

                Hi all tested U101 no power going in or out,
                Q101 tests ok showing 25 ohms on each leg ,
                having fun trying to test resistors tho some reading open then reading resistance if i swap leads about ??
                Am going to desolder them and test off the board .

                Comment

                • PlainBill
                  Badcaps Legend
                  • Feb 2009
                  • 7034
                  • USA

                  #9
                  Re: flatron L1915s

                  Originally posted by sabre504
                  Hi all tested U101 no power going in or out,
                  Q101 tests ok showing 25 ohms on each leg ,
                  having fun trying to test resistors tho some reading open then reading resistance if i swap leads about ??
                  Am going to desolder them and test off the board .
                  Stop!!! What the dickens are you doing? IF Q101 is reading 25 ohms on each leg something is seriously wrong. If no power is going into U101, again, something is seriously wrong. There is no need to test resistors at this point.

                  1. With the board disconnected from the logic card, resting on an insulating surface, and AC power connected, CAREFULLY measure the voltage across C101. It should be 1.4 times line voltage (if you are in the USA or Canada 120 x 1.4 = 165).

                  2. If you are not getting any voltage across C101, check the fuse. If it is good, CAREFULLY check for AC across the center two leads of BD101. If that reads zero, report and wait for further directions.

                  3. If you ARE getting the correct voltage across C101, measure the voltage at U101 pin 7, using the negative lead of C101 as the ground point.

                  4. If U101 pin 7 still reads 0 volts measure the voltage at U101 pin 7. If that also reads 0 volts wait several minutes (or more) for C101 to discharge, then unsolder 1 end of R108 and measure it's resistance. If correct, report and wait for further directions.

                  By the way, the excellent pictures makes helping a LOT easier.

                  PlainBill
                  For a number of reasons, both health and personal, I will no longer be active on this board. Any PMs asking for assistance will be ignored.

                  Never be afraid to try something new. Remember, amateurs built the ark. Professionals built the Titanic.

                  Comment

                  • sabre504
                    Badcaps Veteran
                    • May 2010
                    • 449
                    • United Kingdom

                    #10
                    Re: flatron L1915s

                    Thanks for the slap Plain bill
                    I must have not been totally with it when i was testing i will start from scratch .
                    But i am getting the correct voltage at the main cap so will go from there
                    Thanks again for the input

                    Comment

                    • PlainBill
                      Badcaps Legend
                      • Feb 2009
                      • 7034
                      • USA

                      #11
                      Re: flatron L1915s

                      Originally posted by sabre504
                      Thanks for the slap Plain bill
                      I must have not been totally with it when i was testing i will start from scratch .
                      But i am getting the correct voltage at the main cap so will go from there
                      Thanks again for the input
                      There was an error in my earlier post. It should read "4. If U101 pin 7 still reads 0 volts measure the voltage at U101 pin 1. If that also reads 0 volts wait several minutes (or more) for C101 to discharge, then unsolder 1 end of R108 and measure it's resistance. If correct, report and wait for further directions."

                      Before the SMPS starts, U101 pin 7 (Vcc) gets it's power from U101, pin 1. If U101, pin 1 is low, either R108 is defective, or U101 is defective.

                      PlainBill
                      For a number of reasons, both health and personal, I will no longer be active on this board. Any PMs asking for assistance will be ignored.

                      Never be afraid to try something new. Remember, amateurs built the ark. Professionals built the Titanic.

                      Comment

                      • sabre504
                        Badcaps Veteran
                        • May 2010
                        • 449
                        • United Kingdom

                        #12
                        Re: flatron L1915s

                        Hi got around to starting from scratch all test ok up to u101
                        Pin 7 showing no voltage but pin 1 has 283 volts so must assume u101 is
                        not working so will get another but am going to check my working LG board and see if it has one i can borrow to make sure.
                        Will report back when i have done this

                        Thanks all

                        Comment

                        • sabre504
                          Badcaps Veteran
                          • May 2010
                          • 449
                          • United Kingdom

                          #13
                          Re: flatron L1915s

                          Found another fan7601 taken off a working board
                          Pin 7 showing only 8.5 volts , checked R108 (47k) comes out just under 50k on my meter .

                          No power at the CW201 connector

                          Comment

                          • jetadm123
                            Badcaps Legend
                            • Feb 2010
                            • 2169

                            #14
                            Re: flatron L1915s

                            Originally posted by sabre504
                            Hi got around to starting from scratch all test ok up to u101
                            Pin 7 showing no voltage but pin 1 has 283 volts so must assume u101 is
                            not working so will get another but am going to check my working LG board and see if it has one i can borrow to make sure.
                            Will report back when i have done this

                            Thanks all
                            From what I can see from your photos, it looks like pin 1 of U101 is connected to the main cap through resistor R108. 283V seems a bit low. If your mains voltage is 240VAC, then you should see approx. 240x1.4=336VDC across the main cap.
                            Last edited by jetadm123; 04-16-2011, 09:03 AM.

                            Comment

                            • PlainBill
                              Badcaps Legend
                              • Feb 2009
                              • 7034
                              • USA

                              #15
                              Re: flatron L1915s

                              Originally posted by jetadm123
                              From what I can see from your photos, it looks like pin 1 of U101 is connected to the main cap through resistor R108. 283V seems a bit low. If your mains voltage is 240VAC, then you should see approx. 240x1.4=336VDC across the main cap.
                              Note that he was measuring the voltage at pin 1 of the SMPS controller. The filtered mains voltage is dropped through a 47K resistor, so 283 is not unusual. A 50 volt drop across a 47K resistor means the smps controller is drawing a little over 1 ma.

                              PlainBill
                              For a number of reasons, both health and personal, I will no longer be active on this board. Any PMs asking for assistance will be ignored.

                              Never be afraid to try something new. Remember, amateurs built the ark. Professionals built the Titanic.

                              Comment

                              • PlainBill
                                Badcaps Legend
                                • Feb 2009
                                • 7034
                                • USA

                                #16
                                Re: flatron L1915s

                                Originally posted by sabre504
                                Found another fan7601 taken off a working board
                                Pin 7 showing only 8.5 volts , checked R108 (47k) comes out just under 50k on my meter .

                                No power at the CW201 connector
                                8.5 volts at pin 7 is within the acceptable operating range, but too low for startup to occur. At this point it's hard to tell if the smps controller is trying to start, or was damaged when you removed it from a working board.

                                Points to check - pin 6 of the SMPS controller. If you see intermittent activity, the SMPS is trying to start, but failing. Possibilities are an excessive load, or a shorted diode. There is also a possibility that D102 is bad.

                                Unsolder one end of J1. It provides power for the inverter. If the problem is the inverter, that will remove the load.

                                If that checks out, remove D102. If the voltage at pin 7 starts jumping up and down, D102 is probably leaky.

                                While the chances are extremely remote, check for any solder shorts from replacing the caps.

                                PlainBill
                                For a number of reasons, both health and personal, I will no longer be active on this board. Any PMs asking for assistance will be ignored.

                                Never be afraid to try something new. Remember, amateurs built the ark. Professionals built the Titanic.

                                Comment

                                • sabre504
                                  Badcaps Veteran
                                  • May 2010
                                  • 449
                                  • United Kingdom

                                  #17
                                  Re: flatron L1915s

                                  Ok thanks will check these out and post back .

                                  Will recheck the solder on the caps and reflow to make sure .

                                  Comment

                                  • retiredcaps
                                    Badcaps Legend
                                    • Apr 2010
                                    • 9271

                                    #18
                                    Re: flatron L1915s

                                    Originally posted by PlainBill
                                    While the chances are extremely remote, check for any solder shorts from replacing the caps.
                                    I just did a Benq repair yesterday. After I replaced the new c5707 transistors I tested them with a multimeter and noticed a short. I rechecked my soldering and saw a solder bridge. Luckily I checked my work otherwise I would be redoing all the work again.
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                                    Comment

                                    • sabre504
                                      Badcaps Veteran
                                      • May 2010
                                      • 449
                                      • United Kingdom

                                      #19
                                      Re: flatron L1915s

                                      HI well rechecked everything ,
                                      again the pin 7 on the ic is showing 0 volts so am going to put this to one side while i order some new ones.

                                      Thanks for all the input so far will update when the new parts arrive

                                      Comment

                                      • bcstedt
                                        Senior Member
                                        • Jun 2011
                                        • 59
                                        • Canada

                                        #20
                                        Re: flatron L1915s

                                        I'm working on the same unit. The back-light will flash on about 5 seconds after power is applied, just long enough to see that the monitor is working.

                                        A quick visual reveals one bulging cap (C203 Samxon 680u 25V 105C) and the board is baked dark brown between T301 and T302 (centered around HS301 HS302). I'll take some measurements and update as I go along. Thanks for all the info here.

                                        Comment

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