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AOC LV243XIP 23.8 inch Monitor Screen Flickering

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    AOC LV243XIP 23.8 inch Monitor Screen Flickering

    Hello,
    AOC LV243XIP 23.8 inch Monitor screen flickering after power on monitor within few seconds and image disappear, if power off and on again then then image come back and again disappear within few seconds, i had checked all capacitor which seems ok to me, i have doubt something wrong with LCD board and mainboard is ok, i don't have other same monitor so i check and verify either LCD have issue or mainboard,
    shall highly appreciated any hep to fix this monitor,
    PS. i had attached pics and short video for reference,
    Video Youtube Link: https://youtu.be/z9hIq7UjjIo
    Thank.
    Attached Files

    #2
    Re: AOC LV243XIP 23.8 inch Monitor Screen Flickering

    Sounds like a backlight issue with the LEDs.
    Does the monitor's power LED show that the monitor is ON when you give it signal on either VGA/HDMI/Dp? If so, it more than likely is an LED backlight issue - that could mean either bad LED's in the backlight strips or bad LED driver circuit on the main board. You can also check to see if a picture/image on the screen is visible if you shine a flashlight on at an angle up close.

    I suggest first focusing on the main board, as that would be easier to check. In particular, check (and/or replace) all of the small electrolytic capacitors shown in this picture:
    https://www.badcaps.net/forum/attach...9&d=1644797723
    These are for the LED backlight driver circuit, and if they are bad, they will prevent the backlight from working normally. If you have an ESR meter, report back what values you got for those caps. If you don't, try heating the area where those caps are with a hair dryer and then try powering ON the monitor. If it works, then those caps are most certainly bad. If it doesn't power, then you'll have to remove them to check them (if they are really bad / out of specs, hair dryer trick may not work on them.) Let us know what you find from these tests.

    Oh and if you do have an ESR meter, might as well check the rest of the smaller electrolytic caps on the board as well. All of these could be related to the issues you're seeing.
    Last edited by momaka; 02-18-2022, 12:35 AM.

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      #3
      Re: AOC LV243XIP 23.8 inch Monitor Screen Flickering

      Originally posted by momaka View Post
      Sounds like a backlight issue with the LEDs.
      Does the monitor's power LED show that the monitor is ON when you give it signal on either VGA/HDMI/Dp? If so, it more than likely is an LED backlight issue - that could mean either bad LED's in the backlight strips or bad LED driver circuit on the main board. You can also check to see if a picture/image on the screen is visible if you shine a flashlight on at an angle up close.

      I suggest first focusing on the main board, as that would be easier to check. In particular, check (and/or replace) all of the small electrolytic capacitors shown in this picture:
      https://www.badcaps.net/forum/attach...9&d=1644797723
      These are for the LED backlight driver circuit, and if they are bad, they will prevent the backlight from working normally. If you have an ESR meter, report back what values you got for those caps. If you don't, try heating the area where those caps are with a hair dryer and then try powering ON the monitor. If it works, then those caps are most certainly bad. If it doesn't power, then you'll have to remove them to check them (if they are really bad / out of specs, hair dryer trick may not work on them.) Let us know what you find from these tests.

      Oh and if you do have an ESR meter, might as well check the rest of the smaller electrolytic caps on the board as well. All of these could be related to the issues you're seeing.
      Hi momaka, thanks for above suggestion and help, highly appreciated, have you saw this video which i post on youtube https://youtu.be/z9hIq7UjjIo
      This monitor backlight is ok, what problem it do is one connect via hdmi or vga it give picture for few seconds and then image get freeze and disappear slowly and backlight keep stay there, so if I unplug power and put back power cable image come back again for few seconds and gone in same way, as you suggest above i had used hot air temperature 360c air flow 4 but no luck,
      Any suggestions

      Comment


        #4
        Re: AOC LV243XIP 23.8 inch Monitor Screen Flickering

        Ah OK, sorry I missed seeing the video in the first post.

        The screen going to white indicates there may be either an issue with the power supplies on the T-con board (the board attached to the LCD panel, shown in your picture here) -OR- power going to the T-con board may not be stable.

        First check power going to the T-con board. Usually it's either 3.3V or 5V. On your T-con board, near the LVDS connector (the one with all of the colorful wires), there is a fuse (F1) and next to it a test point ("VIN"). Check the voltage on that pin and see if it's stable when the monitor starts "acting up".

        If it's stable, check the voltage on test point "VDD" that's close to round SMT inductor. You should get anywhere from 10-15V there, usually. It's a boosted voltage rail that is created from pulsing "VIN" thorough that round SMT inductor. If the voltage is not stable on "VDD", check dual diodes D2, D3, and D4. Also check all of the ceramic caps for short circuit in that area.
        If nothing is shorted or bad above, measure resistance between the following test points and ground (with power disconnected from the monitor, of course.):
        "VDD"
        "VGH"
        "VGL"
        "VCC18"
        Report back what resistances you get for those, along with all of the information asked above, if you can. Hopefully this should tell us if the issue is on the T-con board or not. However, I still suggest replacing all of the electrolytic capacitors on the main board. The way the image on the monitor disappears / fades out points to a component failing under load. It could be one of those small caps is showing good ESR and capacitance, but failing once loaded with voltage, or it could also be a diode or ceramic cap failing the same way. It could also be the voltage boosting chip on the T-con board (the one next to the round SMT inductor) going bad. The PCB area around it looks a bit darkened... but check the other items first. Hopefully it's not this chip, since it may be harder to find (and replace.) IME, issues with screen going white is usually either related to bad electrolytic caps on the main board or bad ceramic caps on the T-con filtering/generating VDD, VGH, and VGL.
        Last edited by momaka; 02-25-2022, 09:08 PM.

        Comment


          #5
          Re: AOC LV243XIP 23.8 inch Monitor Screen Flickering

          Hi momaka,
          Thank you for further help,
          fuse (F1) have stable voltage, 5V, but VDD main having issue, when LCD power on and image show ok for few seconds voltages are 11V but after few seconds once image faded voltage goes drop to 4.7V and keep stay at 4.7V, i had checked all T-con ceramic caps and none shoes shot in continuity mode, the chip next to SMT inductor is getting little bit hot but not alot,
          dual diodes D2, D3, and D4 only D2 have voltages 11V for few seconds and it also drop to 4.7V and keep stay 4.7V and D3/D4 have have negative voltage -10V for few seconds and gone after few seconds,
          resistance measurements as below,
          Black probe ground, and red probe on test points with below ohms,
          VDD: 2.99K
          VGL: 11.6K
          VGH: 300K
          VCC18: 9.99K => this reading is not stable and it goes OL and the reading loop,

          shall highly appreciated your help,
          Thanks.

          Comment


            #6
            Re: AOC LV243XIP 23.8 inch Monitor Screen Flickering

            Hi Ali, sorry for the delayed response. Somehow I missed this in my inbox.

            So the voltage dropping on VDD from 11V to under 5V is indicating that one or more of the boosted rails are having an issue. 11V for VDD looks acceptable, which is why the image shows normal at first but then disappears when it drops. So it seems something in the circuit is "breaking down" under voltage. The resistances you measured for VDD, VGL, VGH, and VCC all appear normal at a glance.

            Originally posted by Ali101 View Post
            only D2 have voltages 11V for few seconds and it also drop to 4.7V and keep stay 4.7V and D3/D4 have have negative voltage -10V for few seconds and gone after few seconds
            Ok good check there!

            Diode 4 generates VGL on pin 1 (leftmost lower pin on SOT-23 package), so -10V is actually normal and GOOD.

            Diode D2 generates VGH, which should be anywhere from 15V to 35V. Check what voltage you get on test point VGH again. If it never goes above 11V, I would start looking in the circuit there. SMD inductor L2 next to D2 looks like it has ran a little hot. Check the resistance across L2 and make sure it is good (low - under a few Ohms, if not less.) Perhaps also measure the voltage on both sides of L2.

            At this point, I do have to ask: do you have a multimeter that can measure capacitance or a capacitance meter? If yes, that would be very helpful. If you do, desolder and measure the following ceramic capacitors:
            C220
            C221
            C222
            C216
            C218
            Then, if you can, try replacing these with capacitors of similar capacitance. Voltage rating should be 32V or more.

            If you don't have a capacitance meter, then just desolder C220, C221, and C221... after which, try applying about 20-30V DC across them (out of circuit.) Make sure to try this with a current-protected power supply, in case one of these is bad and breaks down.

            Also check the resistance of resistor R216. It shows as "2R2", if I am not mistaken, and therefore should measure 2.2 Ohm. Also check R219 and R220

            As for diode D3, I'm not sure what voltage it generates. Can you try to trace what its 3 pins connect to? It looks like pin 1 on it connects to test point "VGL_UD" (or is it "VGL_UO"). Can you also measure the voltage on that test point?

            Last but not least, can you also check the voltage on test points "VCC18" and "3.3V" (this last one is close to the LVDS connector, next to a small black diode.)
            Last edited by momaka; 03-15-2022, 06:39 PM.

            Comment


              #7
              Re: AOC LV243XIP 23.8 inch Monitor Screen Flickering

              Hello momaka,
              Thank you for your kids help,
              let me quickly check and get back to you,

              Thanks.

              Comment


                #8
                Re: AOC LV243XIP 23.8 inch Monitor Screen Flickering

                Hi momaka,
                I had follow your instructions and below results i got,
                VGH test point have 29V and it drop to 4.2V within few seconds, L2 had 0 resistance, it had 11.8V at start on both side and drop to 4.7V within few seconds, i replaced your advised all caps and nothing changed hence i believe all these caps seems ok,
                R216: 2.8,
                R219: 250K,
                R220: 250K,
                test point vcc18 have 1.8v and it gone within few seconds, test point 3.3V have stable 3.3V
                I replaced L2, i takeout similar SMD inductor from iPhone 6s board and after that Got 11.8V stable and keep stay but after that main IC stat getting hot, LCD have image now but it keep flickering, i take shot video for your reference, is that possible that IC have problem?
                Below short video link,
                https://youtube.com/shorts/G14EeqMSgUY

                Highly appreciated your help,
                Thanks.
                Last edited by Ali101; 03-17-2022, 06:17 AM.

                Comment


                  #9
                  Re: AOC LV243XIP 23.8 inch Monitor Screen Flickering

                  Interesting.
                  What's the resistance to ground on VCC18? The fact that VCC18 goes down means the whole IC is shutting down / resetting. To me, this suggests it is likely working and detecting an overload on one of these generated rails. After changing L2 with the one from the phone, does VCC18 still go out or does it stay stable at 1.8V now?

                  Originally posted by Ali101 View Post
                  I replaced L2, i takeout similar SMD inductor from iPhone 6s board and after that Got 11.8V stable and keep stay but after that main IC stat getting hot, LCD have image now but it keep flickering, i take shot video for your reference, is that possible that IC have problem?
                  I can't say for certain yet, though it is a possibility.
                  The fact that changing L2 makes the monitor now work, however, suggests to me that the IC may still be OK. With the changed L2, you said you get stable 11.8V on VDD. What about VGH and VGL? Voltage there after changing L2? Also, I asked about "VGL_UD" / "VGL_UO" in my previous post. Were you able to get a resistance and voltage reading for that?

                  Lastly, regarding the video... is the image I see on the screen actual video signal from the monitor, or is that a reflection? It's kind of hard to tell, though I think it's the former? And I'm guessing the screen flicker comes and goes with the IC shutting down and resetting every few moments.
                  Last edited by momaka; 03-18-2022, 12:02 AM.

                  Comment


                    #10
                    Re: AOC LV243XIP 23.8 inch Monitor Screen Flickering

                    Hello momaka,
                    thank you for your further help,
                    yes VCC18 have stable voltage 1.8V and resistance 0.268V on continuity mode, and yes after changing L2 VGH have stable 29V and VGL have -7.7V stable, sorry for i forgot to mention VGL_UO in my last post, yes VGL_UO have resistance 0.55V on continuity mode and have voltage -14/-13 but keep keep up and down -14V/13V and not stable,

                    Originally posted by momaka View Post
                    Lastly, regarding the video... is the image I see on the screen actual video signal from the monitor, or is that a reflection? It's kind of hard to tell, though I think it's the former?
                    you mean that white circle on right side? that is room ceiling light shadow, LCD is ok, just have small white line which moving let and right and one stable light blue line, and of course that screen flicker,
                    Attached Files
                    Last edited by Ali101; 03-18-2022, 01:19 AM.

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