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    #1

    LG 22W2234S troubleshooting and spare parts

    Hi,

    the monitor works fine for some time - sometimes even several minutes - until it acts as if power was turned off - ie., image disappears and the green power led goes off.

    I took a look inside. Previous owner had already attempted to fix the display by replacing electrolytic capacitors (excluding the one big fella) on the power pcb. Only thing that caught my eye was that many solder spots had pretty dull surface hue just like cold joints. Everything seemed to be firmly attached though.

    The fact that the display power stayed on for several minutes straight before losing both image and led power seemed to suggest the origin of this problem is located somewhere on the right half of the pcb.

    Next I began measuring voltages from the IC near the upper-right corner on the back side (note that I've swapped the back side image to help with visual component alignment), before and after the power-out phenomenon. I got some value differences measured before - BANG, I must've accidentally shorted two pins with a dmm probe, successfully rendering at least three resistors and the damn IC dead

    Now I'm short a 2-watt 0.43 ohm metal film resistor and a LD7522PS IC. They seem pretty hard to find online.

    Any help to find spare parts and thoughts on where the source of the original problem might be much appreciated. Maybe I could add two of these parallel as a replacement resistor (0.5 ohm vs 0.43 ohm)?

    IC datasheet
    Attached Files
    Tags: None
    #2
    Re: LG 22W2234S troubleshooting and spare parts

    Wow, I may have found a supplier for LD7522PS in Bulgaria, via google.

    http://www.ksp-electronics.com . I've already registered and placed an order. Apparently they have manual order processing system as I haven't received any email confirmation or payment details. Gotta keep waiting...

    Comment

      #3
      Re: LG 22W2234S troubleshooting and spare parts

      I recognize some Panasonic FC/FK in there, that look genuine.
      What are the other caps?

      Comment

        #4
        Re: LG 22W2234S troubleshooting and spare parts

        Originally posted by munuainen View Post
        Wow, I may have found a supplier for LD7522PS in Bulgaria, via google.
        Bulgaria..... of all places! Leadtrend is terrible at supplying the aftermarket. It seems that they're only interested in dealing with the OEM market.

        It sounds as if your problem is heat related. You turn the system on and the parts heat up and something opens or shorts or changes value causing a shutdown.

        If you get it up and running to where you had it prior to your "accident" try measuring the output voltages at the wiring harness in the upper right. Once it shuts down measure the harness voltages again and the voltage across the large blue cap (Be careful with the HIGH VOLTAGE across the blue cap!).
        Last edited by jetadm123; 08-13-2010, 02:20 PM.

        Comment

          #5
          Re: LG 22W2234S troubleshooting and spare parts

          I recently, had a similar fault,and the problem was the LOGIC board and not the PSU/Inverter board.You don't need the Logic board to check the PSU/Inverter...Putting AC mains onto the board,works evrything LESS the inverter,by plugging the Backlights in,and then applying 3volt DC(from a battery) between the Ground and the On/Off on the top right connector,should switch the lamps on,and confirm whether or not the fault is on the PSU/Inverter.

          Comment

            #6
            Re: LG 22W2234S troubleshooting and spare parts

            After further investigation it's not a metal film but a metal oxide film type I need (the original has non-reflective matte surface). Fortunately, there are ones valued pretty close to 0.43 ohm available at ebay http://cgi.ebay.com/20pcs-Metal-Oxid...-/130333019945

            Comment

              #7
              Re: LG 22W2234S troubleshooting and spare parts

              Ok, I got the replacements. Install the IC and resistors. Connect power - BANG! Oops, I mixed resistor places. Replace resistors with correct placing, connect power - BANG! Oops, shorted due to having forgot to trim the legs after soldering. Good job. At least the IC is still intact.

              After I finally got everything set up, the red-red-silver-gold resistor keeps still blowing up at the moment power is connected. Something I haven't yet noticed must have also gone wrong when the IC was shorted

              The original R805 was carbon 0.2 ohm, the new one is metal oxide 0.22 ohm. The original R815 was 0.43 ohm, the new one is 0.47 ohm. I assume these modifications should not cause the explosion? I'm a complete beginner in electromagnetics so what comes to troubleshooting the problem....well, not going to happen on my own. Any ideas what to do?

              Attached are close-ups of the area where the culprit probably must be. I've again swapped the back side shot so following signal routing should be a bit easier.
              Attached Files

              Comment

                #8
                Re: LG 22W2234S troubleshooting and spare parts

                Originally posted by munuainen View Post
                Ok, I got the replacements. Install the IC and resistors. Connect power - BANG! Oops, I mixed resistor places. Replace resistors with correct placing, connect power - BANG! Oops, shorted due to having forgot to trim the legs after soldering. Good job. At least the IC is still intact.

                Attached are close-ups of the area where the culprit probably must be. I've again swapped the back side shot so following signal routing should be a bit easier.
                You need to slow down and double/triple check your work. Rushing leads to mistakes. Luckily this time, there was no damage, but next time you could be reaching for the fire extinguisher or checking into the emergency room.

                Check ZD802 to make sure it is not shorted. And check D802.
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                  #9
                  Re: LG 22W2234S troubleshooting and spare parts

                  Originally posted by retiredcaps View Post
                  You need to slow down and double/triple check your work.
                  Yes, sir. Can't really argue with that.
                  Originally posted by retiredcaps View Post
                  Check ZD802 to make sure it is not shorted. And check D802.
                  Both diodes appear fine. I'm getting one-way reading in DMM diode measurement setting.

                  Comment

                    #10
                    Re: LG 22W2234S troubleshooting and spare parts

                    Follow PCBONEZ's checklist and test each

                    https://www.badcaps.net/forum/showpo...15&postcount=2
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                      #11
                      Re: LG 22W2234S troubleshooting and spare parts

                      Ok, I'm going to quote Krankshaft's message entry by entry to make sure I'm working on the correct component(s).
                      Originally posted by Krankshaft View Post
                      Line fuse (Continuity Check)
                      This must be the only fuse, F801. It's fine, no resistance whatsoever.
                      Originally posted by Krankshaft View Post
                      Check for open startup resistors (Ohms Resistor Check)
                      Are these the resistors I replaced? If so, then they are fine.
                      Originally posted by Krankshaft View Post
                      Line Rectifier (Diode Check)
                      This is the large rectangular diode D801. This is how I measured it: DMM probes connected to plus and minus (on the back side) pins. One way, I get 1.192, whatever unit it is. The other way the diode shows open.
                      Originally posted by Krankshaft View Post
                      Line Filter Capacitor (Ohms Resistor Check The Cap Should Charge Up)
                      The big cap. Charges up fine.
                      Originally posted by Krankshaft View Post
                      Switching Mosfet (Diode Check For Shorted Junctions) also check for input voltage at the mosfet (DC).
                      Aaaaah. I'm getting zero reading (diode check) for all leg pairs no matter which way the DMM probes are. So the mosfet has died in the process?

                      I also noted the other replaced resistor got knocked out cold as well. Maybe a shorted mosfet would explain that too?

                      Comment

                        #12
                        Re: LG 22W2234S troubleshooting and spare parts

                        On most Monitors,should the main Mosfet go short circuit,then it usually takes out the Gate resistor,and possibly the Source one as well.

                        Comment

                          #13
                          Re: LG 22W2234S troubleshooting and spare parts

                          Originally posted by munuainen View Post
                          Are these the resistors I replaced? If so, then they are fine.
                          If you start at the AC plug and follow the path, PCBONEZ testing instructions will make sense. These are the resistors closest to the AC plug.

                          This is the large rectangular diode D801. This is how I measured it: DMM probes connected to plus and minus (on the back side) pins. One way, I get 1.192, whatever unit it is. The other way the diode shows open.
                          I test the bridge rectifier like this. With power off and unplugged.

                          1) set your multimeter on ohm
                          2) number the rectifier pins 1 to 4
                          3) put black on 1, red on 2 - record ohm
                          4) put black on 1, red on 3 - record ohm
                          5) put black on 1, red on 4 - record ohm
                          6) put black on 2, red on 3 - record ohm
                          7) put black on 2, red on 4 - record ohm
                          8) put black on 3, red on 4 - record ohm

                          Aaaaah. I'm getting zero reading (diode check) for all leg pairs no matter which way the DMM probes are. So the mosfet has died in the process?

                          I also noted the other replaced resistor got knocked out cold as well. Maybe a shorted mosfet would explain that too?
                          I test mosfets for shorts by going s-g, s-d, d-g.
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                            #14
                            Re: LG 22W2234S troubleshooting and spare parts

                            Originally posted by retiredcaps View Post
                            If you start at the AC plug and follow the path, PCBONEZ testing instructions will make sense. These are the resistors closest to the AC plug.
                            Not counting the thermistor RT801 the first resistors are exactly the ones that blew up.

                            Originally posted by retiredcaps View Post
                            I test the bridge rectifier like this. With power off and unplugged.
                            Ohm readings won't keep steady. I guess I should desolder the component to get reliable readings.

                            Originally posted by Rtech
                            On most Monitors,should the main Mosfet go short circuit,then it usually takes out the Gate resistor,and possibly the Source one as well.
                            Symptoms pretty much match the description here.

                            Thanks to both of you for taking the time to assist! I could use some more help identifying the mosfet. Attached is the image. I couldn't find datasheets or anything with the exact code (2763I ?) on the component. Maybe this is the one? http://www.digchip.com/datasheets/pa...763-01-pdf.php
                            Attached Files

                            Comment

                              #15
                              Re: LG 22W2234S troubleshooting and spare parts

                              Originally posted by munuainen View Post
                              Not counting the thermistor RT801 the first resistors are exactly the ones that blew up.
                              I believe the RT801 should read around 30 ohms.

                              Ohm readings won't keep steady. I guess I should desolder the component to get reliable readings.
                              As long as the bridge rectifier comfortably reads well over 200 ohms, it is probably good and thus no need to desolder.
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                                #16
                                Re: LG 22W2234S troubleshooting and spare parts

                                Originally posted by munuainen View Post
                                I couldn't find datasheets or anything with the exact code (2763I ?) on the component. Maybe this is the one? http://www.digchip.com/datasheets/pa...763-01-pdf.php
                                This might be the datasheet for 2763

                                http://pdf1.alldatasheet.com/datashe...SK2763-01.html

                                If correct, now you have the correct specs to find a replacement.
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                                  #17
                                  Re: LG 22W2234S troubleshooting and spare parts

                                  Actually, I found a thread on google. The correct mosfet is http://www.a-power.com.tw/ProductDetails.asp?M_ID=157 . Unfortunately they are pretty hard to find

                                  Comment

                                    #18
                                    Re: LG 22W2234S troubleshooting and spare parts

                                    Originally posted by munuainen View Post
                                    Actually, I found a thread on google. The correct mosfet is http://www.a-power.com.tw/ProductDetails.asp?M_ID=157 . Unfortunately they are pretty hard to find
                                    How about this for a replacement?

                                    http://search.digikey.com/scripts/Dk...e=FQH8N100C-ND

                                    Maybe send digikey an email with both PDFs and ask them if they think it will work. If not, ask them to make a suggestion.
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                                      #19
                                      Re: LG 22W2234S troubleshooting and spare parts

                                      Thanks for the link. Good news: I found a Chinese eBay seller who had AP2761I-As for sale. I sent him a message about if he could get AP2763s and got a fast response saying he's already got them and that he can list them right away. I already purchased two, just in case. I'll have to get back to this topic once they arrive which is probably going to take another two weeks.

                                      Thanks for all the help I've already received!

                                      Comment

                                        #20
                                        Re: LG 22W2234S troubleshooting and spare parts

                                        Originally posted by munuainen View Post
                                        I'll have to get back to this topic once they arrive which is probably going to take another two weeks.
                                        I suggest testing the replacements upon arrival to make sure they are not shorted.

                                        While you are waiting, this would be a good time to check the other components "in circuit" in case something else is shorted by the bad FET.
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