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Acer x223w first white screen, now no backlight

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    #21
    Re: Acer x223w first white screen, now no backlight

    Originally posted by teri3s View Post
    Scale was set to 10x
    I'm curious. Can you remeasure the n channel mosfets "in circuit" with your digital multimeter?

    I have nothing against analog multimeters, but I'm curious if you get the same 50 ohm reading on the digital.
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      #22
      Re: Acer x223w first white screen, now no backlight

      I just rechecked CN801 (plugging in the logic board this time) with the digital multimeter against the ground where the plug is and I get

      While off
      1) 5.05v (VCC 5V)
      2) 5.05v (VCC 5V)
      3) 0V (GND)
      4) 0V (GND)
      5) 0.03V (on/off)
      6) 2.56V (Brightness)
      7) 0.04V (Vol) -----no speakers on this monitor
      8) 1.75V (Mute)

      While on
      all other pins are the same values except
      5) 3.12V (on/off)

      Brightness voltage is the same
      Last edited by teri3s; 10-11-2011, 05:50 PM.

      Comment

        #23
        Re: Acer x223w first white screen, now no backlight

        Not even sure how to explain the testing of the mosfets. Pretty much every combination has the display unchanging from '1' except with ohms set at 200k, with the black probe at S1 and the red probe at D1 I get a number that keeps ascending. I tried discharging the gate with my finger first, but right now the number is 33.5 ohms ascending.

        The behaviour of both mosfets is identical, seemingly synchronized.

        Comment

          #24
          Re: Acer x223w first white screen, now no backlight

          Okay, let's do another simple test.

          Hookup a working computer displaying your favourite wallpaper to the lcd. Do you see the wallpaper even briefly? If you turn off all the lights and shine a flashlight onto the lcd, do you see the wallpaper?
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            #25
            Re: Acer x223w first white screen, now no backlight

            Okay, um.............tried a few times to make sure......and I'm not seeing anything displayed on the screen while shining the flash light on it in the dark.

            Comment

              #26
              Re: Acer x223w first white screen, now no backlight

              Okay, here is what we have tested so far and looks okay.

              1) n channel mosfets do not seem shorted
              2) picofuse is good
              3) inverter transformer readings (secondary) are good
              4) secondary inverter voltages are present (the 17.x V DC seems correct - each manufacturer/board varies).

              The only thing I can think of is the 16 pin IC on the back of the board. What is the part number of that chip?
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                #27
                Re: Acer x223w first white screen, now no backlight

                Originally posted by retiredcaps View Post
                Okay, here is what we have tested so far and looks okay.

                1) n channel mosfets do not seem shorted
                2) picofuse is good
                3) inverter transformer readings (secondary) are good
                4) secondary inverter voltages are present (the 17.x V DC seems correct - each manufacturer/board varies).

                The only thing I can think of is the 16 pin IC on the back of the board. What is the part number of that chip?
                The messy white gray screen mentioned in the first post is interesting; its making me think there may be more than 1 problem.
                The backlight on and dim voltages look to be correct, so I am wondering why no backlights?
                I see a couple of jumpers on the back side of the power supply J509 and 510 that the solder looks bad. One of those could be power or ground to the 16 pin backlight controller.
                Hopefully there will be a data sheet on the 16 pin controller.
                Whatever I do, I consider it a success, if in the end I am breathing, seeing, feeling and hearing!

                Comment

                  #28
                  Re: Acer x223w first white screen, now no backlight

                  That 16 pin IC is difficult to read, it looks like OZ9938GN. Googled it to see what would come up and came across this

                  Pin 2 (VDD based on the datasheet) to ground reads as 240 ohms.

                  OZ9938GN Datasheet
                  Last edited by teri3s; 10-11-2011, 07:15 PM.

                  Comment

                    #29
                    Re: Acer x223w first white screen, now no backlight

                    This shouid be the data sheet.

                    never mind you found it
                    Attached Files
                    Whatever I do, I consider it a success, if in the end I am breathing, seeing, feeling and hearing!

                    Comment

                      #30
                      Re: Acer x223w first white screen, now no backlight

                      Would you expect a voltage on the brightness pin, when the unit is NOT switched on,and then does not change when it is switched on ???,I have not seen this Monitor, but the Dim/Brightness voltage comes from the Logic on a lot of monitors, is that not the case here then ??

                      Comment

                        #31
                        Re: Acer x223w first white screen, now no backlight

                        Originally posted by Rtech View Post
                        Would you expect a voltage on the brightness pin, when the unit is NOT switched on,and then does not change when it is switched on ???,I have not seen this Monitor, but the Dim/Brightness voltage comes from the Logic on a lot of monitors, is that not the case here then ??
                        You seem to be missing a couple of points.

                        1. Most monitors combine all control functions into the graphics processor.

                        2. The processor is always 'on'; the power required is minimal - the backlight and the display panel consume the most power.

                        3. The brightness is set by the output of a D/A converter. Once set, no additional processing is required to maintain it.

                        4. Whether or not the brightness voltage is maintained when the monitor goes into standby is at the whim of the programmer. Clearly, it must be set when the monitor comes active; it isn't clear that turning it off serves any useful purpose.

                        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

                          #32
                          Re: Acer x223w first white screen, now no backlight

                          Bill, thanks for that, unfortunately I misread Post 22,must be having one of those Blonde,but rapidly turning Grey days ...

                          Comment

                            #33
                            Re: Acer x223w first white screen, now no backlight

                            Hrmmmmm.......I've been running some tests on the OZ9938GN chip and it seems to demonstrate some odd behaviour. Elsewhere I found someone recommending grounding either the 'Timer' on Pin 3 or the 'Overvoltage Protection' on Pin 7 to test if the problem is the backlight tubes, the inverters or the IC.

                            After ground Pin 3 or Pin 7 the voltage reading from VDDA (supply voltage input) Pin 2 was 3.14V. (With the monitor 'off' the reading is 2.41V) Backlight still was not on and transformers were not getting warm.

                            I unplugged the monitor and then after plugging it back in and turning on, testing VDDA again the voltage wouldn't rise above ~2.6V.

                            Pin 10 the ON/OFF control of the IC was hovering around ~2.8V.

                            I was puzzled so I cycled the power and so on. Still same results. I put my finger on the IC and it seemed to be a bit warm now.

                            Checking the No. 6 pin (Brightness) at CN801 it remained at ~2.41V.

                            I'm letting the chip cool and will try it again to observe its behaviour.

                            Edit:
                            After letting it cool, not grounding any pins, the reading from VDDA is 3.42V, Pin 10 On/Off 3.1V

                            After about 10mins the readings from the IC were still the same. But checking CN801 Pin 1 and 2 VCC5v read 4.83V. So I found that weird and switched the monitor off. I checked VCC5V and it was now reading 5.03V.

                            Switching the monitor back on the IC's VDDA remained at ~2.6V and the On/off pin 2.9V.
                            CN801's VDD5v pins read 4.83V.

                            Power cycling the monitor from its switch and unplugging don't seem to change this behaviour. Only after unplugging it for several minutes does it seem to let OZ9938 come "on".
                            Last edited by teri3s; 10-12-2011, 07:27 AM.

                            Comment

                              #34
                              Re: Acer x223w first white screen, now no backlight

                              What voltage rating are the capacitors in the inverter area?
                              Did you re-solder those jumpers?
                              Are you seeing above 12 volts at the inverter fuse?
                              Whatever I do, I consider it a success, if in the end I am breathing, seeing, feeling and hearing!

                              Comment

                                #35
                                Re: Acer x223w first white screen, now no backlight

                                Which one is the inverter's fuse?

                                Comment

                                  #36
                                  Re: Acer x223w first white screen, now no backlight

                                  F802 on the top of the P/S
                                  Whatever I do, I consider it a success, if in the end I am breathing, seeing, feeling and hearing!

                                  Comment

                                    #37
                                    Re: Acer x223w first white screen, now no backlight

                                    VDAA (pin 2) is very low. Recommended voltage is 4.5-5.5 volts.

                                    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

                                      #38
                                      Re: Acer x223w first white screen, now no backlight

                                      It started doing something weird where one rail would get sufficient power and the other wouldn't. Power LED going amber if there was 5V on the 5V rail, but then the 18V rail (or whatever its supposed to be) would drop to 17 something volts.

                                      Then sometimes when you cycled the power, the 18V rail would be sufficiently powered and the power led would go blue, but the 5V would be under 5V. Now the power LED went off completely and the voltages across the board are just haywire, fluctuating rapidly but far below what they should be.

                                      All in all its beginning to sound like the other stories about bad caps. I probably just caught it early on or something.

                                      Unfortunately getting replacement caps around here isn't so easy, so I'll have to wait a while. The monitor wasn't even used that much before having this issue.

                                      E-caps from inverter side:

                                      Samxon GK(M)
                                      2x 420uF 25V
                                      1x 1000uF 10V

                                      Su'Scon
                                      1x 470uF 10V

                                      Lelon H823(M)
                                      1x 1000uF 25V
                                      Last edited by teri3s; 10-12-2011, 11:44 AM.

                                      Comment

                                        #39
                                        Re: Acer x223w first white screen, now no backlight

                                        I just plugged in the power board by itself and smoke started emanating from that transformer (T502) on the bottom left side. I noticed it getting warm yesterday.

                                        Recommendations?

                                        Comment

                                          #40
                                          Re: Acer x223w first white screen, now no backlight

                                          Nevermind, it was both N-channel mosfets U501 and U502 trying to basically melt

                                          Comment

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