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    Hyundai L90D+ inverter mosfet problem

    Hi there !

    I would like to thank you first for this great forum, I learn a lot here on LCD repair !

    I recently found a dead 19" Hyundai L90D+ that I really would like to fix and I think I'm getting closer to this.
    Here is what's the problem : just after plug in the power cord, the blue power led turns on. About 5 seconds later, this same led quickly turns to orange and everything shutdown like if a short has come (I can also hear a tick at this time). So, this process restart and loop forever. No Backlight at all.

    Looking to the power/inverter board doesn't show me bulged caps, and anyway it looks like more a MOSFET issue.
    I disconnected it from the logic board, the ticking stop and I get a good 12V and 5V at pins header without shutdown.

    Then, I hooked SLP to 5V and the backlight starting to flash.
    This drive me to the solder side of the board where I can find two dual NP mosfet (U4 and U5) named APM9932 (datasheet here ). Looking closer, I can also see a damaged smd capacitor just nearby U5 (C23). So I suspect something in that area to be the failure.

    Since I cannot find service manual for this monitor, I don't really know what value is C23 nor what kind of mosfet can substitute these APM9932 (can't find them on Digikey or Mouser). And anyway, I'm not an hardcore mosfet calculator.... :p So I need your help on this point !


    Am I right on what I have done ? Any advices else ?

    Many thanks in advance !
    Attached Files

    #2
    Re: Hyundai L90D+ inverter mosfet problem

    to solve one of your problem C53 and C23 should have the same value. The circuit is symmetrical. As for the AP9932 try FairChild website cross reference

    Hope this help
    ecking767

    Comment


      #3
      Re: Hyundai L90D+ inverter mosfet problem

      Test the driver FETs with a DMM are either of them shorted?
      Elements of the past and the future combining to make something not quite as good as either.

      Comment


        #4
        Re: Hyundai L90D+ inverter mosfet problem

        It's discharge capacitor, I think.

        But exact value - I don't know. I found correct value by searching MOSFET datasheet.

        https://www.badcaps.net/forum/showthread.php?t=5346

        Comment


          #5
          Re: Hyundai L90D+ inverter mosfet problem

          Originally posted by Krankshaft
          Test the driver FETs with a DMM are either of them shorted?
          Just try this, and it seems that U4 is shorted on P channel. I've got 0v from D to S and S to D, that's it ?

          Thanks to ecking767 and dondrusco for your tips guys ! I do not know this ability on Fairchild website ! Unfortunately, it doesn't return me anything with APM9932.

          So, a 0.1 uF capacitor for C23 will be good ?

          Comment


            #6
            Re: Hyundai L90D+ inverter mosfet problem

            Hi Lydux,

            I have an identical monitor with exactly the same symptoms and am going to attempt to repair it - did you have any success with yours?

            Cheers

            Comment


              #7
              Re: Hyundai L90D+ inverter mosfet problem

              Hello! The APM9932 is available through Ebay, item 200446667412. It also looks like the seller ships worldwide. Hope this helps.

              Comment


                #8
                Re: Hyundai L90D+ inverter mosfet problem

                I too have the same problem with this board. Did you get it working by replacing the APM9932 FET's and C23 and C53 cap's?

                Comment


                  #9
                  Re: Hyundai L90D+ inverter mosfet problem

                  Just received the FETs yesterday - will give this a go in the next few days...

                  Comment


                    #10
                    Re: Hyundai L90D+ inverter mosfet problem

                    I got 7 of the L91D in with one mosfet shorted. APM9932. SMD caps are all OK. judging fromm ESR readings I guess they are 1 uF or close.
                    Not easy to find these FETs. However, I just finished a batch of 40 IBM 9417-hb7 made by Samsung with fried mosfets and some shorted zeners.
                    They use SI4532DY (mouser 512-SI4532DY; $0.37 in hundred) Current rating is lower than the APM9932 but they do the same job. Customer was in a hurry so I used these in the Hyundai's. Temps are normal, all 7 have been in burn-in all day. Unless one fails day 2 burn-in I will return them to the customer day after tomorrow. This customer requests the "cheapest fix" so it is either trash them or take a chance the sub will hold up.
                    Mike

                    Comment


                      #11
                      Re: Hyundai L90D+ inverter mosfet problem

                      Well, I went ahead and ordered the APM9332's from eBay. Installed them this evening, and the monitor is working great! The caps weren't even bad, just the FET's.

                      Comment


                        #12
                        Re: Hyundai L90D+ inverter mosfet problem

                        Finally got around to replacing the APM9932 FET that was shorted in my monitor - put it all back together and everything is working perfectly so far - thanks to all for pointing me in the right direction.

                        Comment


                          #13
                          Re: Hyundai L90D+ inverter mosfet problem

                          I replaced my APM9932 in my L90D+ with the same problem about a month ago and it worked fine...only to have it die again today. Do you guys think the op-amp (I believe it was labeled LM351) below the fried APM9932 might be causing the problem?

                          Comment


                            #14
                            Re: Hyundai L90D+ inverter mosfet problem

                            I have just gotten in 5 L91Ds with the typical flashing power LED symptom. Either flashes yellow then off or yellow, blue, then off. Anyway, i wanted to try the MOSFET fix, and have found some on ebay. Can someone point me to the component and save my eyesight! I have the monitor cracked open. A pain, but easy enough i guess. Thanks in advance.

                            Comment


                              #15
                              Re: Hyundai L90D+ inverter mosfet problem

                              Originally posted by packratjohn View Post
                              Can someone point me to the component and save my eyesight! I have the monitor cracked open.
                              In post #1, it is picture 3. U5 to the right of the circled component. U4 is to the left of it. Both are 6 pins.

                              Did you try testing the MOSFETs to see if they are shorted first?
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                                #16
                                Re: Hyundai L90D+ inverter mosfet problem

                                No, really haven't done any component testing. Just got these in, and got one opened up to look for the obvious cap problem. I've read this site enough to know to come here first! Not familiar with MOSFET testing, haven't done much. A little direction would be great, and an idea as to what else i might expect to see. I can do board work, including SMD (to a point). Just need guidance. Thanks again

                                Comment


                                  #17
                                  Re: Hyundai L90D+ inverter mosfet problem

                                  Originally posted by packratjohn View Post
                                  Just need guidance.
                                  First, you need to find the datasheet for the MOSFET so you know the pinouts. Here it is

                                  http://pdf1.alldatasheet.com/datashe...C/APM9932.html

                                  Second, there is a thread re testing MOSFET

                                  https://www.badcaps.net/forum/showth...ht=mosfet+test

                                  Third, I like to do simple resistance test from S to G, G to D, and S to D. If these tests show low ohms (say less than 200 ohms), then I get suspicious and do further tests.
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                                    #18
                                    Re: Hyundai L90D+ inverter mosfet problem

                                    Finally got around to testing. Resistance isn't particularly low. Cut to the chase, what are the odds of the 9932 MOSFET solving the problem? Do i just go for it based on the experience of others? Or is there a possibility that C23 is bad? I've worked on laptops for years, and now trying to expand to LCDs. So far had great luck, but i don't hesitate to ask the experts, either! I have 5 of these, and would like to get them going again. Thanks to all.

                                    Comment


                                      #19
                                      Re: Hyundai L90D+ inverter mosfet problem

                                      Originally posted by packratjohn View Post
                                      Finally got around to testing. Resistance isn't particularly low.
                                      Post your resistance measurements and how you tested it.

                                      Cut to the chase, what are the odds of the 9932 MOSFET solving the problem? Do i just go for it based on the experience of others?
                                      Well if the tests show that the MOSFETs are not the problem, why replace them?
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                                      If you are new to this forum, we can help a lot more if you please post clear focused pictures (max resolution 2000x2000 and 2MB) of your boards using the manage attachments button so they are hosted here. Information and picture clarity compositions should look like this post.

                                      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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                                        #20
                                        Re: Hyundai L90D+ inverter mosfet problem

                                        Finally got to sit down with the monitor. Here is what i found:
                                        S1 - D1 > 100k
                                        G1 - D1 > 200k
                                        S1 - G1 > 200k

                                        S2 - D2 = 101k
                                        G2 - D2 = 122k
                                        S2 - G2 = 19k

                                        These are in-circuit results. I can pull the chip and retest it you think that would give more valid results.

                                        This is based on the pinout for the 9932 as shown in the datasheet. As mentioned, i have 5 of these I'd really like to get going, so any good ideas will be greatly appreciated. My local electronics shop, which carries tons of parts, didn't have a cross for the 9932. I think they use NTE.
                                        Last edited by packratjohn; 09-02-2010, 05:25 PM. Reason: ommission

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