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Mag LT916s Model 900p 19" LCD dropping like flies

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    Re: Mag LT916s Model 900p 19" LCD dropping like flies

    Originally posted by A Man
    Yes, pin 4 is on the ground side of the cap and shows continuity. Pin 8 does go to + of the cap through two 23K SMT resistors. When I connect power, I have 16V at this pin. However, I believe pin 5 (not 8) is the driver output for the FET according to the datasheet schematic I attached. But hey, I''ve never done any of this kind of troubleshooting! ... I work on natural gas compressors lol. Anyway, looking at the datasheet for the 7N60B FET, I believe the gate is the pin I circled in blue. I'm having a hard time physically seeing a connection to pin 5 through all of the SMDs but ohming to pin 5 of the SMT IC, I get 10.2 ohms.

    We are making progress, right?
    Yes, we're making progress. First of all, while I RARELY admit to making mistakes, I will admit to typos. And you are right, pin 5 is the drive output. That 8 I posted must have been a typo.

    What is the voltage on pin 6 (Vcc)?

    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


      Re: Mag LT916s Model 900p 19" LCD dropping like flies

      Originally posted by PlainBill
      What is the voltage on pin 6 (Vcc)?

      PlainBill
      0.426VDC to pin 4

      Comment


        Re: Mag LT916s Model 900p 19" LCD dropping like flies

        Originally posted by A Man
        0.426VDC to pin 4
        That leads me to believe the controller is defective. There should be approximately 10 volts on that pin. Check to verify the power FET is not shorted, and none of the output diodes are shorted. The part is inexpensive - only $1.15 from Mouser. Unfortunately, it's on backorder.

        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


          Re: Mag LT916s Model 900p 19" LCD dropping like flies

          Originally posted by PlainBill
          That leads me to believe the controller is defective. There should be approximately 10 volts on that pin. Check to verify the power FET is not shorted, and none of the output diodes are shorted. The part is inexpensive - only $1.15 from Mouser. Unfortunately, it's on backorder.

          PlainBill

          I'm not sure about the IGBT 7N60B... Using the diode check in circuit, it shows 0.795V from gate to emitter and 1.326V from gate to collector w positive lead on gate. If I put the negative lead on the gate, it measures 0.645V from gate to emitter and open from gate to collector. There are two other diodes that check ok.

          Any other tests or suggestions? What exactly is happening (or not!) in this circuit? This is my first SMPS to ever work with. From my understanding the controller pulses the FET which causes the transformer/coil to "fire".

          Comment


            Re: Mag LT916s Model 900p 19" LCD dropping like flies

            Originally posted by A Man
            I'm not sure about the IGBT 7N60B... Using the diode check in circuit, it shows 0.795V from gate to emitter and 1.326V from gate to collector w positive lead on gate. If I put the negative lead on the gate, it measures 0.645V from gate to emitter and open from gate to collector. There are two other diodes that check ok.

            Any other tests or suggestions? What exactly is happening (or not!) in this circuit? This is my first SMPS to ever work with. From my understanding the controller pulses the FET which causes the transformer/coil to "fire".
            That's not the terms I would use to describe it's operation, but you are essentially correct.

            Rectified line voltage is applied to pin 8. The pair of resistors are optional. A constant current source charges the cap connected to pin 6 until it reaches 12.8 volts. At that time it turns on the FET, feeding energy into the transformer primary. The transformer secondaries are rectified, and one of them is used to control an optoisolator which feeds the voltage sense input on the controller. A separate input is used to limit the current through the FET. A tertiary winding on the transformer is rectified and used to charge the cap connected to pin 6.

            One characteristic of this controller is the start-up cycle. The constant current source charges the cap until it reaches 12.8 volts. It then turns off. In normal operation the tertiary winding will provide power to operate the SMPS controller. If that fails to happen (bad FET, shorted diode, etc), the constant current source will kick in again when the voltage across the cap drops down to about 5 volts, and again charge the cap up to 12.8 volts.

            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


              Re: Mag LT916s Model 900p 19" LCD dropping like flies

              I apologize if this question has been answered or perhaps I needed to create a new thread. I am having the same issues has described in this thread, how exactly does one get into/take apart/open(whatever the term is)this LCD? Opening it has been the hardest part thus far.

              Thank you

              Comment


                Re: Mag LT916s Model 900p 19" LCD dropping like flies

                Originally posted by Curious View Post
                how exactly does one get into/take apart/open(whatever the term is)this LCD?
                Careful with the connectors, but something like

                http://www.youtube.com/watch?v=ZvQdY...eature=related
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                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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                Comment


                  Re: Mag LT916s Model 900p 19" LCD dropping like flies

                  Originally posted by retiredcaps View Post
                  Careful with the connectors, but something like

                  http://www.youtube.com/watch?v=ZvQdY...eature=related
                  Thank you!!

                  Comment


                    Re: Mag LT916s Model 900p 19" LCD dropping like flies

                    I hope it will help You...
                    Attached Files

                    Comment


                      Re: Mag LT916s Model 900p 19" LCD dropping like flies

                      I have a Monitor MA-982KC Model 900P. This monitor comes on for about 2 to 3 seconds then the screen goes black, no sign of a picture can be seen, even in a dark room or with a torch. With the monitor connected to a computer a full picture can be seen until the screen goes black. Voltages on the pins of the plug 5v OK, 12v OK Bri reads 2.8v even when the screen black. Blon reads 3.96v, when the screen goes black this drops to zero. When the screen goes black the power LED turns orange. Have changed the 6 x 470 micro fahad capacitors, 1 x 220 micro fahads, 2 x 100 micro fahads and 2 x 10 micro fahads.
                      and the problems remains the same.
                      Any comments would be appreciated.

                      Comment


                        Re: Mag LT916s Model 900p 19" LCD dropping like flies

                        Originally posted by keithf2 View Post
                        I have a Monitor MA-982KC Model 900P.
                        Post clear focused pictures after reading

                        https://www.badcaps.net/forum/showthread.php?t=1868

                        You can also try some of the suggestions at

                        https://www.badcaps.net/forum/showthread.php?t=10419
                        --- begin sig file ---

                        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.

                        Please do not post inline and offsite as they slow down the loading of pages.

                        --- end sig file ---

                        Comment


                          Re: Mag LT916s Model 900p 19" LCD dropping like flies

                          Originally posted by keithf2 View Post
                          I have a Monitor MA-982KC Model 900P. This monitor comes on for about 2 to 3 seconds then the screen goes black, no sign of a picture can be seen, even in a dark room or with a torch. With the monitor connected to a computer a full picture can be seen until the screen goes black. Voltages on the pins of the plug 5v OK, 12v OK Bri reads 2.8v even when the screen black. Blon reads 3.96v, when the screen goes black this drops to zero. When the screen goes black the power LED turns orange. Have changed the 6 x 470 micro fahad capacitors, 1 x 220 micro fahads, 2 x 100 micro fahads and 2 x 10 micro fahads.
                          and the problems remains the same.
                          Any comments would be appreciated.
                          This problem is on the logic card, the fact that the LED goes yellow with signal present demonstrates that. Changing the caps on the power supply may eliminate that; what brand and series did you use?

                          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


                            Re: Mag LT916s Model 900p 19" LCD dropping like flies

                            Originally posted by PlainBill View Post
                            This problem is on the logic card, the fact that the LED goes yellow with signal present demonstrates that. Changing the caps on the power supply may eliminate that; what brand and series did you use?

                            PlainBill
                            Capacitors are marked NRSA, CE 85 degree, (M), T0258.
                            Keith

                            Comment


                              Re: Mag LT916s Model 900p 19" LCD dropping like flies

                              Originally posted by keithf2 View Post
                              Capacitors are marked NRSA, CE 85 degree, (M), T0258.
                              Keith
                              Well, that's part of the problem. The replacement caps aren't close to what the power supply needs to work properly. This threadhttps://www.badcaps.net/forum/showthread.php?t=2280 has information on brands and series of caps that will work. If you live in the US, I recommend buying Panasonic FM caps from Digikey. If you choose USPS First Class Mail shipping the total cost would be about $10.

                              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


                                Re: Mag LT916s Model 900p 19" LCD dropping like flies

                                I tried to send you the circuit diagrams of my 900p monitor, but got a message I did not attache a security tag, how do you do this,
                                keith

                                Comment


                                  Re: Mag LT916s Model 900p 19" LCD dropping like flies

                                  emilije's request:
                                  Attached Files

                                  Comment


                                    Re: Mag LT916s Model 900p 19" LCD dropping like flies

                                    Hi guys. My experiments have lead to the worse: I've completely broken the 32 pin board-to-cable connector, the one in the middle of the circuit board on the TFT panel's back, which is HSD190ME12-A00. Any experience would be extremely welcome: it doesn't look like I could solder those pins back together. Shall I find and replace the entire board - what is its make, find a connector and re-solder it - is it possible to do a 32 pin one with a regular iron, and where to look for such a connector, or maybe its better to just forget about it. Thank you for any input!

                                    Comment


                                      Re: Mag LT916s Model 900p 19" LCD dropping like flies

                                      Originally posted by tollfree View Post
                                      Hi guys. My experiments have lead to the worse: I've completely broken the 32 pin board-to-cable connector, the one in the middle of the circuit board on the TFT panel's back, which is HSD190ME12-A00. Any experience would be extremely welcome: it doesn't look like I could solder those pins back together. Shall I find and replace the entire board - what is its make, find a connector and re-solder it - is it possible to do a 32 pin one with a regular iron, and where to look for such a connector, or maybe its better to just forget about it. Thank you for any input!
                                      Pics of the cables (plus macro shots of the connectors) would be helpful here.

                                      Comment


                                        Re: Mag LT916s Model 900p 19" LCD dropping like flies

                                        Pictures are terrible, sorry. The cable is male, and the on board connector is female -- in pic 6 this broken piece is diagonal above the soldered pins.
                                        Attached Files

                                        Comment


                                          Re: Mag LT916s Model 900p 19" LCD dropping like flies

                                          The picture I've mentioned where you can see the broken piece and soldered to the board pins (kind of see, since pictures are really bad) is "connector 048", and it is # 6 on the list in the previous message. I fill totally lost about that stupid brake and await on help from the experienced people. Be grateful for any input. Thanks.

                                          Comment

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