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Benq G2255 doesn't power on - amber power light when plugged in

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    #81
    Re: Benq G2255 doesn't power on - amber power light when plugged in

    Rddube, you're going to pay the $8 minimum shipping, so you might as well try to get everything in one go. On the through hole caps, pull one leg off of the pcb and check them. 475 ohms sounds low. See what it measures out of circuit. If any doubt, go ahead and get them in this order.

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      #82
      Re: Benq G2255 doesn't power on - amber power light when plugged in

      The one I find suspect is blue and written:
      8
      3KV
      SEC
      Not sure what I should get as I don't see 8pf 3KV capacitors on digikey? By the way, that one is blue but has a yellow tint to it as if it overheated slightly. Anything else I could get if I can't get the exact value?

      Comment


        #83
        Re: Benq G2255 doesn't power on - amber power light when plugged in

        Yes, looks like the closest Digikey has is 10pf. For the discolored blue one, what is the cap number on the board? I believe 2 of those are used to monitor over voltage.

        Also, I mentioned in a previous post that I was concerned about the TG gate driver being on when the chip is down. I was able to find some info on how some of these driver chips function. I don't think you have a problem there, which is good news.

        "When the oscillator is in the off state, the low side MOSFET (Q2) is always conducting due to the IC internal logic. This creates a path for the resonance between the DC blocking capacitor and the transformer primary leakage inductance, which introduces some undesirable noise in the lamp off state."

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          #84
          Re: Benq G2255 doesn't power on - amber power light when plugged in

          It is C817 - I took it out and measured resistance, there is no resistance. Value I get with my fluke multimeter is 32nf and with my multi transistor tester is 17pf.

          I have these other high voltage caps from a Dell monitor scrap board and they are written:
          5C
          3kv

          What do you think?

          Comment


            #85
            Re: Benq G2255 doesn't power on - amber power light when plugged in

            Uhoh, ok i'm tired.
            Last edited by Dumah Brazorf; 01-15-2018, 12:45 PM.

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              #86
              Re: Benq G2255 doesn't power on - amber power light when plugged in

              Originally posted by Dumah Brazorf View Post
              Uhoh, ok i'm tired.
              Dumah, not sure what you mean?

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                #87
                Re: Benq G2255 doesn't power on - amber power light when plugged in

                Wrote something silly then edited out.

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                  #88
                  Re: Benq G2255 doesn't power on - amber power light when plugged in

                  Ordered the parts from Digikey and should be getting them today - incredible 1 day delivery service from Digikey! Will report back once the new Mosfet is installed and the Caps changed. Hope this fixes that issue, and if so, will have to start thinking about the other issue of the mainboard.....

                  Comment


                    #89
                    Re: Benq G2255 doesn't power on - amber power light when plugged in

                    Hello gentlemen,

                    There was a delay in the Digikey shipment so only tomorrow or the next day.

                    Started looking at my problem on the main board, and when I measure 3.3V to ground I get 80 ohms. That sounds a bit low, don' t you think. If it is too low, probably what is giving me that amber power switch light when I plug in the monitor. Any ideas what I should be looking at?

                    I inspected the main board but can't find any physical trace of anything. What do you think?

                    Photos attached to this post for convenience.
                    Attached Files
                    Last edited by rddube; 01-16-2018, 08:57 PM.

                    Comment


                      #90
                      Re: Benq G2255 doesn't power on - amber power light when plugged in

                      Originally posted by rddube View Post
                      Hello Dumah,

                      Thank you for your reply. What do you mean by checking the power button? If eeprom issue, how can I fix it?

                      I did plug in the power board and main board only, and the amber light comes on. Checked the voltages on the voltage regulator at top of photo 5 of my second post with photos, and I get 3.3V on left leg, and 1.8V on right leg, so that looks ok.

                      Then I checked the 2 caps on that same board, removed them and they test ok. Resistance at cap legs when installed and removed is 85ohms...does that look normal?

                      Many thanks for your input!
                      The 80 ohms does sound low. Above, you mentioned that the caps measured 85 ohms when removed. That sounds way too low for a good cap. You might want to remove those again and recheck resistance (3V to gnd).

                      Also, please check the area on the back of the board, circled in the pic. Looks like something scraped across the board there.
                      Attached Files

                      Comment


                        #91
                        Re: Benq G2255 doesn't power on - amber power light when plugged in

                        Originally posted by will62 View Post
                        The 80 ohms does sound low. Above, you mentioned that the caps measured 85 ohms when removed. That sounds way too low for a good cap. You might want to remove those again and recheck resistance (3V to gnd).

                        Also, please check the area on the back of the board, circled in the pic. Looks like something scraped across the board there.
                        Hi Will62,

                        Tks for hanging in there. What I meant, was that the resistance was 85 ohms on the 3.3V to ground even with the caps removed. The caps I checked with my multi component tester and they tested fine...I also checked their resistance and it was in the kilo ohms, so they are not the culprit. So it has to be something else along the line of the 3.3v rail.

                        As for the picture, here is a closeup of the area with another photo of the underside after cleaning it up with isopropyl alcohol.

                        Will, could you review posts 9 and 10 and tell me what you think?

                        I am also attaching a pdf document of a conversation I found on a Russian website that seems to be discussing a problem with the voltage regulator, but it is a translation so not too sure what some of the words might mean, like fieldwoman? The number on that voltage regulator is very close to mine which is 210151DA and under that number I have 1GC0091. Might spring some thoughts.

                        Still pondering..........
                        Attached Files
                        Last edited by rddube; 01-17-2018, 05:46 AM.

                        Comment


                          #92
                          Re: Benq G2255 doesn't power on - amber power light when plugged in

                          Does it measure the same swapping the probes of the multimeter?
                          Last edited by Dumah Brazorf; 01-17-2018, 12:28 PM.

                          Comment


                            #93
                            Re: Benq G2255 doesn't power on - amber power light when plugged in

                            Rddube,
                            Responding to your questions/points:

                            1. On the Ohms with and w/o caps, understood now.

                            2. Post 9&10: Over my pay-grade to try to explain it (or understand it), but the tl431 controls the optocoupler's path to ground. It varies the intensity of the led. That feedback returns to the high voltage driver IC, which in turn adjusts the PWM to the mosfets. Someone posted earlier that the blue wire may be the power saving signal.
                            I think they were right. It might just be a high or low signal from the main board, which adjusts the tl431. You read ~.77V, which is enough to "turn on" most zeners. You'll never read voltage (0.04V) on the right side, until the left exceeds the "zener/knee" voltage. They may have used it to protect the main board.

                            3. Russian forum translation: What I got out of that, was that the voltage regulator was for 1.8V, and he was getting 2.5-2.8V (regulator hot). He also ended up having to replace the TSUMU58 chip to fix his problem.

                            4. You may not have a problem with the 3.3V on the main board. At the regulator, you read 3.3V in and 1.8V out. The 3.3V is generated on the power board. If you had a short to ground (or ohms too low) on the main board, I'd expect to see a voltage drop at the regulator.

                            Now, when you get a chance, go back to that 1.8V regulator, and check resistance from the 1.8V to the TSUMU58 chip pins 53,74,104 &126.

                            Thanks
                            Last edited by will62; 01-17-2018, 02:02 PM.

                            Comment


                              #94
                              Re: Benq G2255 doesn't power on - amber power light when plugged in

                              Well, total disappointment. Got the Digikey order in, installed the CSD88539ND Mosfet, checked resistance between S1 and D1 - 350K ohms, same with S2 and D2, and gave it a try. Lights did not even flash, nothing.

                              Checked the resistance between S1 and D1 and now get 1.4 Mega ohm...so it's shot.

                              Rechecked the data sheet to make sure I had pin 1 in the right place, but on the datasheet they show a dot but there is none on the mosfet (photo attached). I assumed the line meant the top of the Mosfet which I am pretty sure gives pin 1 where I indicate in the photo.

                              So, this Mosfet doesn't work....shucks.
                              Attached Files

                              Comment


                                #95
                                Re: Benq G2255 doesn't power on - amber power light when plugged in

                                Drain 1, pins 7&8 are tied together, as are drain 2, pins 5&6. They should have 0 ohms between them (7 to 8, 5 to 6). That should tell you where pin 1 is.

                                Comment


                                  #96
                                  Re: Benq G2255 doesn't power on - amber power light when plugged in

                                  Yep, just checked and that is the way I installed it i.e. pin 1 in the right place. They say in the description for this Mosfet:

                                  This dual SO-8, 60 V, 23 mΩ NexFET™ power
                                  MOSFET is designed to serve as a half bridge in low-
                                  current motor control applications.

                                  Probably not the right one?
                                  Last edited by rddube; 01-17-2018, 08:52 PM.

                                  Comment


                                    #97
                                    Re: Benq G2255 doesn't power on - amber power light when plugged in

                                    Yeah, the ones on ebay from China were closer to the fets that you had. The TI one is closest that I could find from Digikey (60V, 7A, 23m, 2.1w). Let it sit for a while. Then get back and check all your voltages, and recheck the fets to make sure they're blown. Check them the way the guy in this video does. (G=p2, D=p8, S=p1)

                                    https://www.youtube.com/watch?v=RkWy1EirEu8

                                    Comment


                                      #98
                                      Re: Benq G2255 doesn't power on - amber power light when plugged in

                                      Ok, so checked the Fet and it turns out it is not cooked, it still gives good readings.

                                      So I rechecked all voltages on the controller chip, all 3 resistors in place, and here is what I get:

                                      Pin 1: 5.85V
                                      Pin 2: .136V
                                      Pin 3: .136V
                                      Pin 4: .092V
                                      Pin 5: .001V
                                      Pin 6: 1.206V
                                      Pin 7: 3.58V
                                      Pin 8: 3.92V
                                      Pin 9: 15.15V
                                      Pin 10: 15.13V
                                      Pin 11: 13.4V
                                      pin 12: 13.6V
                                      Pin 13: 5.89V
                                      Pin 14: 0V
                                      Pin 15: 0V
                                      Pin 16: 5.54V

                                      Tried the power board again connected to the CFL's with all 3 resistors in, nothing happens. Rechecked the FET and it is still good? Rechecked my soldering of the FET to make sure it as good, and all is good.

                                      So not sure what gives.

                                      Comment


                                        #99
                                        Re: Benq G2255 doesn't power on - amber power light when plugged in

                                        Originally posted by Dumah Brazorf View Post
                                        Does it measure the same swapping the probes of the multimeter?
                                        Yes it measures exactly the same thing when swapping the probes 80.4 ohms both ways.

                                        Comment


                                          Re: Benq G2255 doesn't power on - amber power light when plugged in

                                          Time to dust off your DSO138. We need to see if the Mp10091 chip is sending a PWM signal to the mosfet gates. You should probe pin 11 (TG), and then pin 14 (BG). Need a nice square wave on both. If the chip is working, but going into shutdown, the signal won't last more than about a second, so you need to have everything connected and eyes on scope when you turn the power on. Between tests, either drain caps or wait until pins 7 & 9 are near 0V. To avoid accidentally shorting pins and frying the chip, I'd recommend that you trace out to the nearest component and probe there.

                                          There are tons of videos about using the DSO138 on youtube. If you haven't used the scope very much, maybe watch a few videos. We are looking for a square wave of ~12V at a frequency of ~50kHz. A vertical of 5v/div and a horizontal of 10-20us should be OK.

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