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    Samsung 930b LCD cold start problem (inverter?)

    I have a Samsung SyncMaster 930b LCD. I think the "b" just means it's black, so 930 is probably sufficient.

    Starting about a week ago, I noticed that when I turn on the monitor, the backlight stays dark and the green power LED starts blinking rapidly. The speed of the blinking LED is faster than what I'd see if there was simply no input signal. It blinks about twice per second, and only spends a split moment in the ON condition - most of the time the LED is off. If I were to guess, it looks more like power cycling rather than an intentional blink.
    The monitor refuses to turn off when it's doing this - it's stuck trying to power up the backlight unless I unplug it.

    After blinking the LED for several seconds the backlight eventually turned on. As long as I leave the backlight on (power management disabled), then there are no further problems. If I turn it off but turn it back on immediately, it works fine. It's only a problem when it's cold.

    I haven't noticed if the screen is working when the backlight is off.


    This problem has gradually gotten worse each day, taking slightly longer to power up each time.

    Since I started leaving the monitor on constantly, I changed the brightness of my backlight to a much lower setting. Then I absent mindedly turned it off.
    Next time I tried to start it, the cold start problem was much worse, but I don't know if the low brightness setting is just a coincidence.

    I left it blinking for hours and the backlight never came on. Then I propped a lamp up against it and let the bulb heat up the back of the monitor. After doing that, I came back about an hour later and found the monitor working.

    ===============


    Am I correct in assuming this is an inverter problem? How easily do these monitors typically come apart? Can I get to the inverter without disassembling anything else? I really don't want to get dirt into it or have to touch the LCD portion at all, if I can help it.

    For now, I'm just going to leave it on, but someday it will end up turned off again so I might as well find out what I'm up against. Never opened an LCD before and the thought worries me. I suppose it might still be under warranty but I can't find any documentation or packaging whatsoever.
    Attached Files

    #2
    Re: Samsung 930b LCD cold start problem (inverter?)

    Intrems of getting apart look at the videos that can be accessed from this page: http://www.lcdrepair.us/powersupply.html
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      #3
      Re: Samsung 930b LCD cold start problem (inverter?)

      Fixed.

      Seems the LCD screen is sealed off from everything else, so no problem with dirt since I didn't need to go in there.

      The last time this screen ended up cold, I couldn't get it to run anymore, even with a lamp heating it from the back. I ended up melting the plastic trying to heat it up enough to work.
      ===

      With great care and lots of photos, I got it apart. The video input board didn't look have much to look at. <photo attached at bottom>

      Over to the power board, and to my relief I found a bulged Samxon GF cap. Good, should be easy to fix.
      Turns out all the caps are made by Samxon, including the large 100uF 450v input cap and a small 47uF cap (which I didn't notice until looking at the pictures just now).


      The originals caps were:
      2x Samxon GF 1000uF 16V 10x20
      2x Samxon GF 1000uF 25V 10x20
      1x Samxon GF 470uF 25v 10xwhatever
      1x Samxon KM 100uF 450v 18x ~36 (replaced with 18x40)
      1x Samxon ?? 47uF ??v.

      I ordered replacements from digikey for all but the 47uF, which I overlooked. The Samxon GF has the same ESR specs as Chemicon KY, and same standard case sizes. KY is also a high endurance cap, so it seemed perfect.
      Unfortunately, the 1000uF 25V GF's must have been a custom size, because they aren't listed in 10x20 as standard (for either series). I had to order the KY's in 12.5x20 in order to maintain vertical clearance. 10x30 is too tall.

      All replacements are KY series except the large input cap, which is a Chemicon KXG.


      New caps installed:

      Had to tilt things just slightly to get the 12.5mm caps in there, but as expected it wasn't much of a problem.

      Put it back together and I got a flat white screen.

      Damn. Well at least the power is on.

      Took it back apart, turns out this flimsy little video connector wasn't quite latched in right. I had fiddled with it before deciding it didn't need to be unplugged. Photo shows it in proper position, before I had messed it up:

      The metal hooks were unlatched and it was bending to one side a bit. I got it clamped back down, but it sure doesn't seem like a very solid connection.

      Anyway, it works now.


      See attached photos for an overhead of the power board (if anybody cares). I also have a big photo of the back side of the PCB, but I didn't upload it because it's big, and shrinking it would make it useless. If somebody wants to see the trace layout I'll post it.
      Attached Files
      Last edited by gdement; 09-21-2008, 07:42 AM.

      Comment


        #4
        Re: Samsung 930b LCD cold start problem (inverter?)

        930B any of these vintage with "B" is sync on green capable.

        Good save and it is one of these monitors Pentium should look for especially for his oddball computers that uses sync on green signal.

        Cheers, Wizard

        Comment


          #5
          Re: Samsung 930b LCD cold start problem (inverter?)

          Interesting if it's sync on green capable, because if anything I've found this monitor very picky about input signals.

          I have a couple old (~1996 or so) Diamond brand PCI video cards I sometimes use when testing motherboards, and this monitor hates both of them. It usually works okay in higher modes like a Windows GUI, but it blanks out sporadically in lower modes, including the POST and BIOS setup screens. The video just disappears at random intervals - it's extremely annoying.

          Comment


            #6
            Re: Samsung 930b LCD cold start problem (inverter?)

            Sounds like this video card is not programmed correctly for the text mode frequency. I had this problems with video cards that weren't reputable.

            Replace them with reputable video cards like Radeon or different video card to try. Some LCD monitors have limited choices of frequencies especially down low also.

            Cheers, Wizard

            Comment


              #7
              Re: Samsung 930b LCD cold start problem (inverter?)

              Probably, although I thought the old Diamond (pre-3D era, before they went bankrupt) was reputable.
              Next time I'm using one of those cards I'll check the refresh rate on the monitor.

              I had a more severe and obvious refresh defect with a Hercules Geforce2 MX card - it was over by about 5% in all modes. 90Hz in 85Hz mode, 64 in 60 mode, etc. This LCD didn't blank out on that card but it couldn't center the screen with it.

              I wish I had some other really old PCI cards to test against. I'm curious if it's more an issue of age, like something tightened in the specs at some point. But maybe Diamond was just sloppy. Back when people had CRTs I guess it didn't matter much.

              I do have an ancient 1MB ISA card, but I almost never have occasion to use that. Last time I used it, it actually had problems rendering the graphics in the BIOS POST SCREEN. I found that pretty hilarious.

              Comment


                #8
                Re: Samsung 930b LCD cold start problem (inverter?)

                Actually, u need one that is made by reputable brand. Diamond was not one of these.

                Back then, there were too many video card makers that doesn't program the eeprom with correct, vertified timings that follows the VESA specs. I seen this happen.

                My advice: find matrox, ATi or sapphire (radeon series), nvidia reference-based video cards. I had similar complaints from customers with no video or out of range with LCDs and late CRT monitors and I knew it is the eeprom has incorrect video data set up issues.

                Cheers, Wizard

                Comment


                  #9
                  Re: Samsung 930b LCD cold start problem (inverter?)

                  Just for the record ...

                  I asked myself "Why would they put two 15V and two 25V caps in a power supply like this one?" And the most logical answer is that it was an assembly error.

                  It is no cooincedence that I have a Samsung 930B with 'EXACTLY' the same problem and the same capacitor bulging. The photos could have been of my monitor.

                  The conclusion is this. Replace the two 15V 1000uf caps with 25V caps. All 4 should be of the higher rating. If you don't, you will be repairing the monitor again in a few months - for the same reason. The caps are being stressed above their design limits.

                  I can just imagine the assembly line, with people who have no clue how to read arabic numerals, stuffing circuit boards with 4 capacitors that look like, but are not alike. Did you notice that they are physically the same size? And easy mistake to make.

                  If you want the repair to be more reliable, don't just get better caps, get the ones that should have been placed there to begin with.

                  Comment


                    #10
                    Re: Samsung 930b LCD cold start problem (inverter?)

                    Originally posted by checkers1811
                    Just for the record ...

                    I asked myself "Why would they put two 15V and two 25V caps in a power supply like this one?" And the most logical answer is that it was an assembly error.

                    It is no cooincedence that I have a Samsung 930B with 'EXACTLY' the same problem and the same capacitor bulging. The photos could have been of my monitor.

                    The conclusion is this. Replace the two 15V 1000uf caps with 25V caps. All 4 should be of the higher rating. If you don't, you will be repairing the monitor again in a few months - for the same reason. The caps are being stressed above their design limits.

                    I can just imagine the assembly line, with people who have no clue how to read arabic numerals, stuffing circuit boards with 4 capacitors that look like, but are not alike. Did you notice that they are physically the same size? And easy mistake to make.

                    If you want the repair to be more reliable, don't just get better caps, get the ones that should have been placed there to begin with.
                    Good guess, but wrong. The problem is the original caps were garbage. I've only repaired a few LCD monitors, but I've seen the 'bulging cap' problem with 16V caps on a 5V line and 25V caps on a 12V line. Heck, I had one fail that was a 35V cap on a 12V line - and no sign of bulging.

                    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


                      #11
                      Re: Samsung 930b LCD cold start problem (inverter?)

                      Precisely.

                      If I KNOW the voltage on that buses then I can put 16V caps on 12V and 10V or 6.3V on 5V bus. If bus is greater than 16V and is around 22V max, 25V. If greater than that 22V, 35V so on.

                      Cheers, Wizard

                      Comment


                        #12
                        Re: Samsung 930b LCD cold start problem (inverter?)

                        OK, I don't know what this forum's policy is on thread necro but I'm going to bump this thread anyway. Found this via Google BTW.
                        I also have a Samsung 930B that suddenly decided that it didn't want to light. No fuss like the thread's OP monitor had, mine just didn't turn on one morning. Flashlight check showed the panel to be OK, just no backlight. I consider myself to be highly skilled when it comes to repairing minor problems and taking the LCD apart was no problem for me. However, diagnosing capacitors are a bit out of my area of experience. I note from the discussion above that you beleive the use of 15V caps may be a contributing factor in the inverter's demise. Mine uses 10v and 25V caps, but has a different PCB layout (though the components all seem to be the same, just moved/arranged slightly different).

                        My question is this, from looking at the pic below, am I looking at a bad inverter (dead caps) or is my problem the CCFLs? Looks like the green ones are bulged a bit, but I've seen that before on electronics that still worked perfectly fine. I'm fairly handy with a soldering iron, so replacing the caps will pose no problem to me.








                        For reference, here are the CCFLs:

                        Comment


                          #13
                          Re: Samsung 930b LCD cold start problem (inverter?)

                          Originally posted by Chaosratt
                          OK, I don't know what this forum's policy is on thread necro but I'm going to bump this thread anyway. Found this via Google BTW.
                          I also have a Samsung 930B that suddenly decided that it didn't want to light. No fuss like the thread's OP monitor had, mine just didn't turn on one morning. Flashlight check showed the panel to be OK, just no backlight. I consider myself to be highly skilled when it comes to repairing minor problems and taking the LCD apart was no problem for me. However, diagnosing capacitors are a bit out of my area of experience. I note from the discussion above that you beleive the use of 15V caps may be a contributing factor in the inverter's demise. Mine uses 10v and 25V caps, but has a different PCB layout (though the components all seem to be the same, just moved/arranged slightly different).

                          My question is this, from looking at the pic below, am I looking at a bad inverter (dead caps) or is my problem the CCFLs? Looks like the green ones are bulged a bit, but I've seen that before on electronics that still worked perfectly fine. I'm fairly handy with a soldering iron, so replacing the caps will pose no problem to me.
                          My only question is how much money do you want to put into this? The caps are definitely garbage. They were junk when they came from the factory and haven't improved with age. Replace all of them (EXCEPT for the large one (100 uF, 450 Volt?) mounted on it's side). Replacing them with Panasonic FM or FC series should cost you about $10 from Digikey.

                          This may fix it, or it may not. Before you order the caps, check to see if there is a fuse to the inverter section. You might have shorted transistors or just a blown fuse. Good pictures of the bottom of the board would help.

                          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


                            #14
                            Re: Samsung 930b LCD cold start problem (inverter?)

                            $10 is well within my budget for repair. No fuses that I can see (or rather, nothing that looks to be like its a fuse). The bottom has almost no components, mostly just traces but I'll grab a pic of it tomorrow.

                            100 uF, 450 Volt is correct on the big cap.


                            My google searching leads me to believe that LCD inveters and CCFLs are basically the same, and interchangable with, the CCFLs kits used for lighting in computer cases.
                            Would it damage anything to get a cheap CCFL (Say off one of those lighted fan things) and wire it up to the inverter? That would give a quick indication of whether it was the inverter or the CCFL.
                            On that note, do CCFLs have a 'polarity'?

                            Comment


                              #15
                              Re: Samsung 930b LCD cold start problem (inverter?)

                              Originally posted by Chaosratt
                              $10 is well within my budget for repair. No fuses that I can see (or rather, nothing that looks to be like its a fuse). The bottom has almost no components, mostly just traces but I'll grab a pic of it tomorrow.

                              100 uF, 450 Volt is correct on the big cap.


                              My google searching leads me to believe that LCD inveters and CCFLs are basically the same, and interchangable with, the CCFLs kits used for lighting in computer cases.
                              Would it damage anything to get a cheap CCFL (Say off one of those lighted fan things) and wire it up to the inverter? That would give a quick indication of whether it was the inverter or the CCFL.
                              On that note, do CCFLs have a 'polarity'?
                              You have described a common test fixture. I often suggest buying one of the kits and using it to test both the CCFLs and the inverter.

                              CCFLs don't have a polarity in the usual sense. You will notice that one wire to the CCFLs has much thicker insulation. That wire always connects to the high voltage output of the inverter. The other wire is the return line, and goes to the circuit which senses the current through the CCFL.

                              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


                                #16
                                Re: Samsung 930b LCD cold start problem (inverter?)

                                So then, the thicker wire should be the main if possible, but for the -/+ 3 seconds its going to get plugged in it really doesn't matter?
                                Thanx, I'll see what I can do.

                                Comment


                                  #17
                                  Re: Samsung 930b LCD cold start problem (inverter?)

                                  Well I'm now in possession of two of these with the same problem (got a steal on the second one, figured I could fix both and sell one for a profit).
                                  Got the caps in from Digikey and recapped one PSU completely. Power it on and..... nothing. DSP/LCD still kick on (can see the faint "no signal" box with a flashlight), but there's a god-awefull squeal emanating from the PSU now.
                                  Figure I fubar'd the recap (the 100uF's I couldn't match perfectly) I moved to the second PSU and recapped only the bad 820s using the Chemicon KY (exactly matching the OP's repair). Again same deal, everything except the CCFLs come on, and then it squeals. I've test both PSUs with both sets of CCFLs to the same result. These CCFLs also kick on fine when connected to a simple inverter used for aftermarket lighting kits.
                                  Of note, I did NOT replace the large 100uF 470V cap, could this also be bad without showing any physical signs (and thus the stress of the load is shifted to it with the other bad Samxon's replaced?)

                                  I'm realy at a loss here for what else might be bad, or what I may have done incorrectly.

                                  Comment


                                    #18
                                    Re: Samsung 930b LCD cold start problem (inverter?)

                                    Originally posted by Chaosratt
                                    Well I'm now in possession of two of these with the same problem (got a steal on the second one, figured I could fix both and sell one for a profit).
                                    Got the caps in from Digikey and recapped one PSU completely. Power it on and..... nothing. DSP/LCD still kick on (can see the faint "no signal" box with a flashlight), but there's a god-awefull squeal emanating from the PSU now.
                                    Figure I fubar'd the recap (the 100uF's I couldn't match perfectly) I moved to the second PSU and recapped only the bad 820s using the Chemicon KY (exactly matching the OP's repair). Again same deal, everything except the CCFLs come on, and then it squeals. I've test both PSUs with both sets of CCFLs to the same result. These CCFLs also kick on fine when connected to a simple inverter used for aftermarket lighting kits.
                                    Of note, I did NOT replace the large 100uF 470V cap, could this also be bad without showing any physical signs (and thus the stress of the load is shifted to it with the other bad Samxon's replaced?)

                                    I'm realy at a loss here for what else might be bad, or what I may have done incorrectly.
                                    Leave the big alone.
                                    Post a pic of YOUR REPAIRED/RECAPPED BOARD (any of the two you just mentioned)
                                    There are 10 kind of people in this world: those that understand binary, and those who don't.
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                                      #19
                                      Re: Samsung 930b LCD cold start problem (inverter?)

                                      Partial Recap (replaced only the three bulged caps).


                                      Complete Recap (note some of the 100uFs are slightly smaller now.



                                      Original with my diagram to remember which ones went where

                                      Comment


                                        #20
                                        Re: Samsung 930b LCD cold start problem (inverter?)

                                        The Samxon GF plague strikes again !
                                        Elements of the past and the future combining to make something not quite as good as either.

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