LG Flatron L194WT-SFQ:AUSRQF

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  • bipolar
    Member
    • Oct 2011
    • 30

    #1

    LG Flatron L194WT-SFQ:AUSRQF

    Okay, sports fans!

    Our patient this time is an LG L194WT-SFQ:AUSRQF. The Pt presented - wait - this isn't student med...

    This monitor was DoA, and plugging it in showed no soft-start or power. Dead as a doornail. After prying the front bezel off (and breaking three of the top tabs), removing the four screws on the back, and disconnecting the switchboard cable, panel header, and the CCFL plugs, the power PCB was removed.

    See shots 01, 02, and 03. Shots 04/05 are close-ups of the Samxons by the HS. Shots 06/07 are of the bottom, and shot 08 is a side view of C206 (all the 25V caps looked okay, but better safe than sorry, right?). Shots 09/10 are of the AC input, and shots 11-13 show the HV/CCFL drivers and SOIC MOSFETs (which shows some discoloring on the PCB, but nothing unexpected. In fact, everything but those two Samxon 16V caps looked remarkably good. A quick in-circuit check of the MOSFETs and diodes read nominal, so none of those had to be ordered. Still, for reference, I shot photos of the ICs with my "tags" on them, as "lbl1-4".

    As you can see, it's an AIP-0122 rev. D, made by Lien Chang. If you follow the plastic pointer up the board, you'll see the problem(s) in picture 3. Those are Samxon GF(M) series, known to be a bad batch. In PCB order, they are:

    C203 - 680uF, 25V, 10mm dia., 21mm len. (use Digikey # P12390)
    C202/6 - 1000uF, 25V, 10mm dia., 21mm len. (use Digikey # P12379)
    C204/5 - 1000uF, 16V, 10mm dia., 21mm len. (use Digikey # P12366)
    C207 - 470uF, 25V, 10mm dia., 16mm len. (use Digikey # P12388)

    The Samxon caps at C101 (100uF, 450V) and C105 (0.47uF, 50V) are KM series, and looked good. The remaining Samxon GF(M) was at C103 (33uF, 50V), and feeds the FAN7601, so I'm guessing it doesn't see anything higher than 2X mains frequency (120Hz in my case), so I didn't replace it. I did, however, order the closest PanaFM to it, either Digikey # P12925 (33uF @ 35V) or #P12928 (56uF@50V). One is higher capacitance, but lower voltage (the FAN7601 shouldn't be seeing more than about 20V here, but you're still taking chances) - the other has the same voltage, but slightly higher capacitance. My gut instinct tells me they just used the GF(M) here because they had a bunch lying around. Since this is tied to the "soft start" feature, it merely acts a timing mechanism for the inrush current limiting for charging up those other GF(M)s.

    So, about $4.50 of Panasonic (Matsushita) FM goodness later...

    As you can see in shots "panfm1/2", the black-and-gold Panasonic FM goodness is all up in that. The "lone" cap at C206, by the SOIC MOSFETs, was the hardest to unsolder, only because they bent the leads of the cap before soldering it. The others just dropped (literally!) out once the second lead was hit with Solder-Wick (R). This is a single-sided board, and my trusty Radio Shack 30W iron had NO problem dealing with it. In fact, I was surprised by how well both the iron and wick handled the lead-free solder. I did mask out the "Pb Free" note on the PCB, as I used "LotsaLead" solder. Sue me, I'm NOT a "lead-is-dead-head".

    After quadruple-checking my work, I re-installed the PCB, hooked everything back up (except the front bezel, as that thing really, really sucks to take back off), and... SUCCESS!

    I didn't take yet-another-monitor-picture (yamp), but trust me. I ran it for about 90 minutes before calling it fixed. I'd estimate the temp wafting up the back at about 80F (~27C). No pops, crackles, or bad smells, either.

    Hopefully, this helps anyone else with the same situation, or has really botched up their repair and needs a reference to get back on track. Thank you for playing along...

    bipolar
    Attached Files
  • wombat68
    New Member
    • Nov 2011
    • 2

    #2
    Re: LG Flatron L194WT-SFQ:AUSRQF

    You're a legend Bipolar.
    I have 2 LG Flatron 1919s monitors sitting here with exactly the faults you describe.
    I had sussed that it was the power supply caps, but your detailed descriptions have made me decide to have a go at fixing them instead of my usual "throw it away and buy a new one" method of repair....
    I'll let you know how I get on....

    Comment

    • codemonkeyboy
      New Member
      • Aug 2012
      • 1
      • United States

      #3
      Re: LG Flatron L194WT-SFQ:AUSRQF

      Thanks this was super helpful!

      I had a feeling my screen was dead due to something regarding the power of the board. In my old rental house we had issues with the power or storms were occurring when I wasn't home. Eventually I had a power strip go completely and I think it took a few items with it (PSU, graphics card, and this LCD Monitor).

      Comment

      • duttonw
        New Member
        • Sep 2012
        • 1
        • Australia

        #4
        Re: LG Flatron L194WT-SFQ:AUSRQF

        Thanks for the info, sadly postage from digikey costs as much as a new board so i went to the local jaycar here in a australia, they sadly don't carry any 680uf, 25v caps, so i used a 1000uf cap instead. the monitor worked for well over 2 hours when i tested. I have not seen negative effects for this, except for the monitor taking slightly longer to start. I'm guessing the 680uf is connected to the soft power cycle.

        Comment

        • tom66
          EVs Rule
          • Apr 2011
          • 32560
          • UK

          #5
          Re: LG Flatron L194WT-SFQ:AUSRQF

          Just don't expect it to last; the cap will likely fail soon. You have Element14 (Farnell) in Australia right? I heard they now have free postage.
          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

          • pgmadhav
            New Member
            • Feb 2013
            • 1
            • india

            #6
            Re: LG Flatron L194WT-SFQ:AUSRQF

            hey duttonw,
            is the 1000uf still holding or it


            Originally posted by duttonw
            Thanks for the info, sadly postage from digikey costs as much as a new board so i went to the local jaycar here in a australia, they sadly don't carry any 680uf, 25v caps, so i used a 1000uf cap instead. the monitor worked for well over 2 hours when i tested. I have not seen negative effects for this, except for the monitor taking slightly longer to start. I'm guessing the 680uf is connected to the soft power cycle.

            Comment

            • smason
              Badcaps Legend
              • Feb 2010
              • 1652
              • Canada

              #7
              Re: LG Flatron L194WT-SFQ:AUSRQF

              Originally posted by bipolar
              Okay, sports fans!

              Our patient this time is an LG L194WT-SFQ:AUSRQF. r

              Nice job. Looks just like almost every LG I've repaired in the last few years.
              36 Monitors, 3 TVs, 4 Laptops, 1 motherboard, 1 Printer, 1 iMac, 2 hard drive docks and one IP Phone repaired so far....

              Comment

              • albertlc
                New Member
                • Jan 2014
                • 1
                • illes balears

                #8
                Re: LG Flatron L194WT-SFQ:AUSRQF

                guau!!
                searching in google for my lg screen I found this forum and I have just registered to say thank you!!!
                save me just buy a new screen and most importantly, generate a residue.
                regards from mallorca!! mediterranean pearl

                Comment

                • jadana
                  New Member
                  • Apr 2014
                  • 1
                  • Prague

                  #9
                  Re: LG Flatron L194WT-SFQ:AUSRQF

                  Super instructions. My LG Flatron works again
                  Thanks

                  Comment

                  • altar62
                    New Member
                    • Jul 2014
                    • 1
                    • SK

                    #10
                    Re: LG Flatron L194WT-SFQ:AUSRQF

                    Thank you for your guidance, monitor repaired ...
                    Thanks.

                    Comment

                    • cpdump
                      New Member
                      • Nov 2017
                      • 3
                      • France

                      #11
                      Re: LG Flatron L194WT-SFQ:AUSRQF

                      I have LG Flatron L1752TQ with the same power board and same revision, after some research, I found schematic of this board in the service manual (page 35) which can be useful to repair it: https://www.manualslib.com/manual/10...q.html?page=34

                      At first glance C204 is in bad shape on my board, the other Samxon GF(M) capacitors seem OK but I'll replace them anyway.

                      Comment

                      • neisg1
                        Member
                        • Sep 2017
                        • 33
                        • Canada

                        #12
                        Re: LG Flatron L194WT-SFQ:AUSRQF

                        In your Photos 3,4 & 5 I would say you have at least 2 or 3 bulged and or leaking caps best to replace all of them.

                        Comment

                        • cpdump
                          New Member
                          • Nov 2017
                          • 3
                          • France

                          #13
                          Re: LG Flatron L194WT-SFQ:AUSRQF

                          Originally posted by cpdump
                          I have LG Flatron L1752TQ with the same power board and same revision, after some research, I found schematic of this board in the service manual (page 35) which can be useful to repair it: https://www.manualslib.com/manual/10...q.html?page=34
                          At first glance C204 is in bad shape on my board, the other Samxon GF(M) capacitors seem OK but I'll replace them anyway.
                          C204 is in bad shape in second picture, but I'm not sure for the two close to C204, they have green and brown/orange spots on top, I don't know if it's electrolyte leak. Same for C206 on the last photo.
                          Attached Files

                          Comment

                          • cpdump
                            New Member
                            • Nov 2017
                            • 3
                            • France

                            #14
                            Re: LG Flatron L194WT-SFQ:AUSRQF

                            I unsoldered C204 and the 4 capacitors around to be sure. With a transistor tester, I found that C204 was definitively bad (Vloss > 30%; high ESR), the others not so bad but I replaced them anyway. Now, I have a functional monitor

                            Comment

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