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iiyama PSU repair from LCD monitor [fixed]

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    iiyama PSU repair from LCD monitor [fixed]

    I just fixed my iiyama 24" monitor (E2407HDSD) that went off with a bang last week.

    It started buzzing while I was using it but this only lasted 10 seconds before the whole thing went pop. During the buzzing there was no noticeable side effect but I didn't get a chance to turn it off before I realised what was wrong.

    When it popped an ember shot out of the bottom of the power supply. I believe this was from the fuse which really struggled to interrupt the failure current. Probably a cheap ass fuse. Tearing apart the fuse revealed the sand that it was filled with had glassified, so a substantial arc likely formed within it.

    Tearing it down, found the primary switching transistor shorted, no surprise there. It's a simple flyback so that or the bridge rectifier is bad. The driver IC was popped as well - and the part number was unreadable. Thankfully, I found a schematic of a Viewsonic monitor with the same power supply (likely the same OEM as iiyama); PSU board was JT240xx

    https://cdn.badcaps-static.com/pdfs/...ce119f6336.pdf

    So I was able to order a replacement IC and a few replacement transistors. Tried it with my bulb tester and to my dismay whilst there was no light the PSU still did not work.

    Checked a few things and found that the source resistor for the MOSFET was bad. This was 0.27R, I did not have an exact value but I had 0.22R so that was subbed in its place. However upon doing this I was greeted by a glowing bulb and only 12V dc across the main filter cap terminals.

    Testing across there with ohmmeter revealed a 2k ohm "leak" to ground. Removing various parts I eventually found my new MOSFET was leaky. How odd. I am not sure if the open source pin with a driven gate caused this. But it did seem odd. Replacing the transistor fixed this.

    So now I tested the unit. No flash from the bulb and only 250V DC across the filter cap terminals... Odd. However the 5.4V main output is OK and it's enough to make the standby LED glow. I decided to investigate the filter cap after I notice that the cap discharges very quickly once the monitor is unplugged - in less than a second. I am used to this monitor being able to remain in standby for up to 30 seconds after unplugged so this is very odd. I discovered that the positive lead of the very high quality Elite cap had completely corroded and as such the cap was no longer connected.

    This must have been the source of the original failure, as the cap going bad would explain the buzzing. I imagine then the flyback was desperately trying to keep the output under regulation with very low line voltage at times and so working much harder than normal. To its credit I did not notice any flicker on the LCD despite it losing its main source of power. Must have been putting the smaller output caps under some stress! I replaced the 150uF 400V cap with a Vishay BC 220uF 400V cap that I had spare.

    All in all an interesting chain of failures. I suspect the reason the source resistor opened was because the fuse was very slow, and the MOSFET killed the driver IC, all because of a 400V cap went bad.

    And the kicker? I never replaced the 400V cap when I first got the monitor as a freebie - it had two bloated low voltage caps but the 400V one "never goes bad", right? Now I know better! (that red wire on the board is one of the jumper wires I put in to repair some damage I did when I first repaired this monitor. Early days, I was bad at soldering!)
    Attached Files
    Last edited by tom66; 07-27-2018, 11:22 AM.
    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.

    #2
    Re: iiyama PSU repair from LCD monitor [fixed]

    nice fix tom66! the main filter cap(s) rarely go bad, but they do.

    Comment


      #3
      Re: iiyama PSU repair from LCD monitor [fixed]

      Actually with APFC in my experience main filter cap failure is common.
      The cheap cap brands like Elite etc can't handle the stress.
      "The one who says it cannot be done should never interrupt the one who is doing it."

      Comment


        #4
        Re: iiyama PSU repair from LCD monitor [fixed]

        The original cap was rated at 400VDC? That's cutting it close! Most main caps for these supplies are at least 450VDC.

        Comment


          #5
          Re: iiyama PSU repair from LCD monitor [fixed]

          Funny and interesting repair job. Glad to hear you got it working, though.

          Indeed it's rare for the input bulk caps to go bad, as CapLeaker said - at least in non-APFC PSUs... but it can happen. I think heat can play a big factor in this one. I fixed a Daewoo L700C monitor for a friend a while back (I think my second LCD monitor repair actually, and the first one I posted on BCN if anyone is curious to look), and that one had a Samxon primary cap which I don't know if it read in spec at the time of removal (due to not having any way to measure it). But many years later now with the cap seeing occasional testing use in my parts bin, I do notice that it doesn't stay charged for too long and the capacitance is borderline okay. So looks like crap caps in hot monitors can have problems - even the input bulk ones.

          Unfortunately, with some LCD monitors being so cheap, it's almost not worth doing on smaller and less-than-special LCD monitors.

          Originally posted by Per Hansson View Post
          Actually with APFC in my experience main filter cap failure is common.
          The cheap cap brands like Elite etc can't handle the stress.
          Agreed.

          But does this PSU even have APFC?

          If it does, I would also measure the voltage across the cap too. jetadm123 has a valid point that the cap should be rated for at least 450V if the PSU has APFC. If the voltage gets anywhere too close to the cap's rating, a sudden failure like that shouldn't be too surprising.

          Comment


            #6
            Re: iiyama PSU repair from LCD monitor [fixed]

            This failure has nothing to do with over voltage or such.
            The legs have corroded off, it's a fucked up electrolyte formula that attacks the aluminium.
            I have seen several such failures, don't post about them all of course but here is one:
            https://www.badcaps.net/forum/showpo...07&postcount=1
            "The one who says it cannot be done should never interrupt the one who is doing it."

            Comment


              #7
              Re: iiyama PSU repair from LCD monitor [fixed]

              Indeed, the high voltage mains filter cap leaking from the anodic lead in APFC circuits, both in LCD monitors and in AC adapters, is quite common. I’ve seen this happen with both Elite (Chinsan), Ltec, and even Taicon (it seems to happen whether the capacitors are rated for 400V, 420V, or 450V). I’m not sure if high voltage caps have issues with foil corrosion, though, or at least not in the way that the low voltage water-base electrolytes do. CapXon high voltage caps also had similar issues, where the anodic foil connected to its respective terminal lead is shot.

              I’d guess the issues lies with the cheaper plated foils that these “high” quality brands are using - they simply can’t handle the stress of very high voltage applications.

              Comment


                #8
                Re: iiyama PSU repair from LCD monitor [fixed]

                Originally posted by jetadm123 View Post
                The original cap was rated at 400VDC? That's cutting it close! Most main caps for these supplies are at least 450VDC.
                It's not an APFC power supply so at 265V AC in (maximum rated voltage for EN standard) the peak voltage across the filter cap will be 375V DC.

                If the unit has APFC then the boost voltage is generally set at 390V. This is sufficiently above the highest expected DC input voltage so the circuit can operate always in the boost mode.

                With those designs there's anywhere from 10V to 20V of ripple on the bus voltage so they usually use a 420V or 450V cap to give the design sufficient margin.
                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


                  #9
                  Re: iiyama PSU repair from LCD monitor [fixed]

                  Just a crap capacitor, but that also shows a marginal design of the PSU. A few months ago, I fully recapped a Fujitsu Siemens monitor built in 2006 that i use as my secondary at work, because it had a wavy pattern over the picture.

                  The primary cap was corroded like you found, but it worked like that for a long time. It had been in storage for a while but I remember it being used and having that wavy pattern 3 years ago when I first got employed here, so it had likely been bad for a long time but it kept on running. The CCFLs are still perfect btw.
                  Originally posted by PeteS in CA
                  Remember that by the time consequences of a short-sighted decision are experienced, the idiot who made the bad decision may have already been promoted or moved on to a better job at another company.
                  A working TV? How boring!

                  Comment


                    #10
                    Re: iiyama PSU repair from LCD monitor [fixed]

                    Originally posted by Th3_uN1Qu3 View Post
                    A few months ago, I fully recapped a Fujitsu Siemens monitor built in 2006 that i use as my secondary at work, because it had a wavy pattern over the picture.

                    The primary cap was corroded like you found, but it worked like that for a long time. It had been in storage for a while but I remember it being used and having that wavy pattern 3 years ago when I first got employed here, so it had likely been bad for a long time but it kept on running. The CCFLs are still perfect btw.
                    Wow really?!

                    Could you describe the "wavy pattern" in more detail? Reason I ask is because I have a "West Wing" -branded LCD monitor (FSP board with CapXon KFs that I recapped with Panny FMs, except the big input cap - also a CapXon) that started doing something similar (I think) about a year or two ago - on a full white screen, you can see some darker patterns moving up and down, and especially when the HDD on the computer is doing something or when I have the scanner plugged in and scanning. Almost looks like some sort of EMI/RFI. I kept dismissing it up to this point to just interference and/or marginal cable design, even though the analog/VGA cable I am using is original with an old OEM Dell (BenQ) monitor. I've also auto'd the monitors input to make sure it's in sync with the signal (as I've had LCD monitors looks pretty wavy and blurry when plugged to a new computer and not auto-adjusted). Does that sound like a bad input cap?

                    Comment


                      #11
                      Re: iiyama PSU repair from LCD monitor [fixed]

                      did you recap the invertor?
                      that sounds like the backlights are picking it up.

                      Comment


                        #12
                        Re: iiyama PSU repair from LCD monitor [fixed]

                        Inverter is on the same PCB as the PSU, and I recapped the entire PSU minus the main input cap. Thus, the filtered 12V output from the PSU goes straight to the inverter (and also the logic board, where it is buck-regulated down to 3.3V and lower.)

                        Comment


                          #13
                          Re: iiyama PSU repair from LCD monitor [fixed]

                          Originally posted by momaka View Post
                          Wow really?!

                          Could you describe the "wavy pattern" in more detail? Reason I ask is because I have a "West Wing" -branded LCD monitor (FSP board with CapXon KFs that I recapped with Panny FMs, except the big input cap - also a CapXon) that started doing something similar (I think) about a year or two ago - on a full white screen, you can see some darker patterns moving up and down, and especially when the HDD on the computer is doing something or when I have the scanner plugged in and scanning. Almost looks like some sort of EMI/RFI. I kept dismissing it up to this point to just interference and/or marginal cable design, even though the analog/VGA cable I am using is original with an old OEM Dell (BenQ) monitor. I've also auto'd the monitors input to make sure it's in sync with the signal (as I've had LCD monitors looks pretty wavy and blurry when plugged to a new computer and not auto-adjusted). Does that sound like a bad input cap?
                          I've seen exactly the same issue when the VGA cable is a bit crap, or in a really rare case on a desktop PC where the bulk cap failed leading to loads of 100Hz making its way onto the 12V & 5V rails.

                          If it were the monitor itself, I'd expect the wavyness to be relatively constant, not varying.
                          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


                            #14
                            Re: iiyama PSU repair from LCD monitor [fixed]

                            Originally posted by tom66 View Post
                            I've seen exactly the same issue when the VGA cable is a bit crap
                            Yes, I've thought about that too, and it's possible. Though again, the VGA cable is the original one that came with a Dell desktop (+ LCD monitor), so I expect it to be decent. And besides, I'm only pushing 1280x1024 resolution, not anything higher.

                            I guess I might try another monitor with this same cable and see if the issue remains. I doubt it would, though.

                            Originally posted by tom66 View Post
                            or in a really rare case on a desktop PC where the bulk cap failed leading to loads of 100Hz making its way onto the 12V & 5V rails.
                            I'll check on that with another PSU. However, the PSU in the desktop that is currently connected to the monitor is an older HiPro tank with PPFC and 2x 200V caps (voltage doubler), so I don't think those would be bad. But I will check when I have time.

                            Originally posted by tom66 View Post
                            If it were the monitor itself, I'd expect the wavyness to be relatively constant, not varying.
                            The wavyness is constant in terms of size. But it varies in the position found on the screen (that is, it seems to move up and down). And only noticeable on a light screen.

                            Comment


                              #15
                              Re: iiyama PSU repair from LCD monitor [fixed]

                              The same kind of wavy pattern you are describing was displayed on my Fujitsu monitor. Replace the primary capacitor and it should be good.
                              Originally posted by PeteS in CA
                              Remember that by the time consequences of a short-sighted decision are experienced, the idiot who made the bad decision may have already been promoted or moved on to a better job at another company.
                              A working TV? How boring!

                              Comment


                                #16
                                Re: iiyama PSU repair from LCD monitor [fixed]

                                Thanks for the reply. Will do that next month hopefully and report back (currently away from said monitor.) Will probably make a thread on it too, just for the sake of not hijacking this one any further.

                                Comment


                                  #17
                                  Re: iiyama PSU repair from LCD monitor [fixed]

                                  I have same monitor, Can you help me? Mine is totally DEAD, i replaced the Mosfet , IC which is ld7576PS , every cap, big+small ones, i replaced blown fuse and my monitor is still completely dead. on output from PSU to inverter i have 5Volts and one is 3.3V I think. Is that Correct?

                                  Comment


                                    #18
                                    Re: iiyama PSU repair from LCD monitor [fixed]

                                    I need to confirm if my PSU is OK.

                                    Comment


                                      #19
                                      Re: iiyama PSU repair from LCD monitor [fixed]

                                      We need to see the pictures of the whole top and bottom side of YOUR board.
                                      Did you read post #1?
                                      Last edited by budm; 09-18-2018, 09:46 AM.
                                      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


                                        #20
                                        Re: iiyama PSU repair from LCD monitor [fixed]

                                        Yes i did. And pictures of my board are in my newly created post

                                        Comment

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