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Dell 1707FPt No Power

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    #81
    Re: Dell 1707FPt No Power

    If I recall correctly you replaced the startup cap on the old board - I think restarting is a symptom a bad startup so can you replace this one?
    Please upload pictures using attachment function when ask for help on the repair
    http://www.badcaps.net/forum/showthread.php?t=39740

    Comment


      #82
      Re: Dell 1707FPt No Power

      Originally posted by LDSisHere View Post
      I think your 5V output fluctuating is due to no load being on the supply. When the back lights are on, the supply has a load so the voltage is stable, when they go off it has no load so it becomes unstable. If the fluctuating 5V is bothering you, try connecting a 100 ohm resistor between it and ground and see if it stabilizes. I would also try driving the back lights on with the supply voltage using a 100 ohm resistor between the 5V and "ON" pin, opposed to an external voltage source if that is what you are using.

      When the CCFL's were on for three minutes did any one of the four bulbs flicker or dim before the other three just before it went out?

      It may help if you took a picture of your test while it is in progress.
      I tried driving the ccfls with the PS 5v w/ a 100 ohm resistor, nothing happened. Connected external 4.7v & lights flash on, then off for 2 sec. & repeat, for about a minute, then nothing. I was able to snap a picture during a brief sec they were on. Here also is picture of my external power source.

      selldoor - I think restarting is a symptom a bad startup so can you replace this one?
      Yes I can & I will. I actually have not checked all the caps on this new board, but I will.
      Attached Files

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        #83
        Re: Dell 1707FPt No Power

        Did you ever get a chance to check/change the startup cap on your board? If so did that fix your problem?

        Comment


          #84
          Re: Dell 1707FPt No Power

          I checked all caps. ESR was great, most even lower than the panasonic FM caps I have to replace them with. I've resoldered ever pin coming thru the board. Checked mosfets and transistors, none shorted. Invertor transformers check 443ohm & 442ohm. The best I can get it to do is flash full on for a second, then off for 2 seconds, but it will do that consistanlly. Make for good Christmas lighting. One question, what sort of voltage should I expect on the pins of the power transistor, the one screwed to heatsink by the large cap? I've got big voltage on the source, drain, and gate pin.

          Comment


            #85
            Re: Dell 1707FPt No Power

            Well, I threw the towell in on my new crappy board and ordered another off ebay. Got it here today, connected spare backlights, external 3.1vdc, it worked perfect. Connected logic board, connected AC, montior came on without me pushing the button, and would not turn off. Crap. I did get to see monitor display something, "DELL display perfection", ya, I got other words for it. I didn't have monitor connected to computer, and it never went to standby, just stayed green LED until I unplugged it. Then plugged back in, no LED light. I noticed the ribbon connector form buttons to board didn't look too good. Is there a way to fix this problem? I've inserted & removed this ribbon many times, it didn't use look like this.
            Attached Files

            Comment


              #86
              Re: Dell 1707FPt No Power

              What I would do (after practicing on some scrap ribbon cable first) is recreate "new" leads above the old ones by scraping the plastic off the copper, then trim the end of the cable to where it is flush with the shortest lead. It should not be too hard but it may take a few tries to find the right tools and technique which is why I suggest practice on an old cable first.

              Comment


                #87
                Re: Dell 1707FPt No Power

                I would make sure that bit of solder, that is missing isn't shorting anything out.

                it could be stuck in there.

                Comment


                  #88
                  Re: Dell 1707FPt No Power

                  Originally posted by LDSisHere View Post
                  What I would do (after practicing on some scrap ribbon cable first) is recreate "new" leads above the old ones by scraping the plastic off the copper, then trim the end of the cable to where it is flush with the shortest lead. It should not be too hard but it may take a few tries to find the right tools and technique which is why I suggest practice on an old cable first.
                  Thanks neighbor (I'm just across the state line from you), I'll give it a try.

                  Amraks; I would make sure that bit of solder, that is missing isn't shorting anything out.

                  it could be stuck in there.
                  I thought about that, Ive looked in with a large glass, can't see anything. I've blown it out, but will do some more.
                  Thanks

                  Comment


                    #89
                    Re: Dell 1707FPt No Power

                    I was really curious about the problem with the power boards for this monitor so I asked Maybenever if I could try my hand at working on one of them, He agreed and sent me his original power board.

                    Before I every applied power to the board I decided to check the semiconductors for shorts or anything unusual. When I got to Q105 and Q106 some of the readings I was getting seemed odd but I could not tell if this was a problem with the transistors or caused by the surrounding circuits. To test them properly I removed them from the board. Q106 seemed to be fine, Q105 however had a pair of legs that would conduct in both directions in diode mode so it was bad. I found a replacement on an old power supply that I used.

                    Before I tested the board with power applied I had to figure out the connectors pinout. I marked the picture of the connector on the bottom of the board with what each pin does. I805 controls the power to the 12V barrel jack on the side.

                    For my initial tests I was using batteries to power the BL_ON and DIM circuit at ~4.5V. When I did apply power to test it, the CCFL's would flash on and off like a strobe light (2-3 times a second) and voltages all over the board would go crazy including the high voltage side. I wanted to figure out why the primary side was being affected so much. I replaced the bridge rectifier and main cap but that did not alter the behavior. I actually only figured it was the FET Q108 on accident. I was checking voltages on various parts of the primary side with my meter while I was trying to turn the CCFL's on and off. For what ever reason when I had my meter on the FET's drain pin, the CCFL's would come on and stay on but as soon as I removed it they would start going on and off again. Replacing the FET stopped this from happening as long as I was turning them on and off with batteries, but when I tried to use the boards 5V they began flashing again.

                    I discovered that unless the 5V had a load on it to keep it stabilized trying to turn on the CCFL's would still cause them to strobe. If I put a 100 ohm resistor between the 5V and ground I did not have this problem. I could then use resistors setup as voltage dividers (like in my schematic) to turn them on with ~3.5V or directly use the 5V of the supply but without the load resistor I would get the strobe effect.

                    Anyway I thought I would share this in the hope it may help someone else in the future with a similar problem.
                    Attached Files

                    Comment


                      #90
                      Re: Dell 1707FPt No Power

                      Originally posted by LDSisHere View Post
                      I actually only figured it was the FET Q108 on accident.
                      Good job in finding the problem.

                      Remote troubleshooting is extremely difficult and finding a solution through unlikely methods such as above is not something I could have predicted.
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                        #91
                        Re: Dell 1707FPt No Power

                        Having physical access to the board like my case below also led me to find the fault "by accident".

                        https://www.badcaps.net/forum/showthread.php?p=262730
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                        Comment


                          #92
                          Re: Dell 1707FPt No Power

                          Originally posted by LDSisHere View Post
                          I was really curious about the problem with the power boards for this monitor so I asked Maybenever if I could try my hand at working on one of them, He agreed and sent me his original power board.
                          Great Job LDS, and your tip on reworking the end of that ribbon connector going to the button board worked just fine. I've still got a problem on the logic board and don't know what to check now. There are a boat load of fuses on this board, all check good, .05ohm or less. The voltage regulators have proper voltage. I've replaced 4 crap caps, but they weren't that bad, .08ohm ESR. The replacements checked .02ohm ESR. Don't know where to go from here. I marked the caps replaced with red in photo.
                          Attached Files

                          Comment


                            #93
                            Re: Dell 1707FPt No Power

                            Have you checked the voltage at I310? If you could, get some pictures of the back of this board, and the front/back of the button board. Also do a continuity test between the two boards to make sure the ribbon cable is making good contact if you have not done this already.

                            Comment


                              #94
                              Re: Dell 1707FPt No Power

                              Originally posted by LDSisHere View Post
                              Have you checked the voltage at I310? If you could, get some pictures of the back of this board, and the front/back of the button board. Also do a continuity test between the two boards to make sure the ribbon cable is making good contact if you have not done this already.
                              I310
                              BS33P
                              77316
                              When the monitor turns on, I have 5.23vdc at pin 1, 3.29vdc at pin 2. When mointor will not turn on, I've got zero voltage on all pins. When checking between pins, I have 400ohm or more on all combinations.
                              I have checked continuity between the PS & logic board, all good. I have checked between button board and logic board, all good. I have 3.28vdc present on some of the pins going to the button board. I will have to get some pictures made of button board.

                              Comment


                                #95
                                Re: Dell 1707FPt No Power

                                I recorded the voltages on the button ribbon connector of the logic board.
                                Pin 1 = .00v
                                """ 2 = .00v (sometimes .50v and quickly droping to zero)
                                """ 3, 4, 5, 6, & 7 = 3.24v
                                """ 8 = ground
                                Here are pictures of back of logic board and both sides of button board.
                                Attached Files

                                Comment


                                  #96
                                  Re: Dell 1707FPt No Power

                                  From what I am seeing it looks like each button has a corresponding capacitor. I would see which pins go to C601, one side should be ground. I would then power on the monitor and check it for voltage, with and without the button being pressed.

                                  What you need to determine is if the power button is sending a signal to the main board to power on and if it is, where is the signal stopping. You will also have to determine if the power on signal is active high or active low. For example on a PC, the PS_ON is pulled low (grounded) when the power button is pressed to turn on the PC power supply.

                                  Comment


                                    #97
                                    Re: Dell 1707FPt No Power

                                    Originally posted by LDSisHere View Post
                                    From what I am seeing it looks like each button has a corresponding capacitor. I would see which pins go to C601, one side should be ground. I would then power on the monitor and check it for voltage, with and without the button being pressed.

                                    What you need to determine is if the power button is sending a signal to the main board to power on and if it is, where is the signal stopping. You will also have to determine if the power on signal is active high or active low. For example on a PC, the PS_ON is pulled low (grounded) when the power button is pressed to turn on the PC power supply.
                                    Thanks LDS. I was pretty far down the rabbit hole with this monitor, I decided to go $10 more. I got a logic board from recycle&save (ebay), the same outfit I got the second PS board. Connected everthing, it works. Powered it off and on a few times, it goes into stanby mode (amber LED) like it should. Connected it to a computer, all seems to be fine. I didn't have much time to compare voltage points just yet, although I plan to before puting all back together. I did take time to check I310 voltage reg, when monitor is powered off, there is no voltage there. But there is 3.24v on pin 11 of the PS board (next to the inverter on pin). By the way here is a picture of that ribbon I fixed with your help. Any ideas on further determining what is wrong with old logic?
                                    Attached Files

                                    Comment


                                      #98
                                      Re: Dell 1707FPt No Power

                                      I am glad you were able to get it working. You probably could learn a lot if you use the working one to compare with the bad one. Just be careful that you do not accidentally damage the working board in the process. It is easy for the meter probes to accidentally touch two pins at the same time.

                                      The ribbon cable looks good. You may want to consider tinning the copper to prevent oxidation.

                                      Comment


                                        #99
                                        Re: Dell 1707FPt No Power

                                        Originally posted by LDSisHere View Post

                                        The ribbon cable looks good. You may want to consider tinning the copper to prevent oxidation.
                                        Any tinning plastc ribbon tips?

                                        Comment


                                          Re: Dell 1707FPt No Power

                                          Originally posted by maybenever View Post
                                          Any tinning plastc ribbon tips?
                                          Practice on a old ribbon.
                                          Flux the copper.
                                          Put a very small amount of solder on the tip of your iron.
                                          Start at the end closest to the plastic then move the iron to the end like you are drawing a line with a pencil. You do not want to linger with the iron in one place. You just want the solder thin as possible, use just enough to color the copper silver.

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