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OKI ES7411 Laser Color printer with 44201901YB power supply

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    OKI ES7411 Laser Color printer with 44201901YB power supply

    Hi:

    I have 2 OKI ES7411 printers.

    - First one doesn't do anything. No sound, no standby light....nothing
    - Second one the power supply seems to switch on (I am able to hear the relé). In the front panel a green light is shown, but nothing in the LCD is shown. So from testing purposes it's also dead.

    I started to dissemble the first one. And here are the pictures from the SMPS.

    The first thing I've noticed when I swith the SMPS on is that the RELÉ is not activated, so the main input does not get to the bridge rectifier. From your experience, what activates the RELE? the SMPS itself or something external from the PCB?

    In the meantime, I will be checking individual components and also I will compare with the second SMPS.

    Regards,
    Francesc.
    Attached Files

    #2
    Re: OKI ES7411 Laser Color printer with 44201901YB power supply

    on the totally dead one, start by replacing the 3 capacitors around the 7pin chip
    thats your standby supply.

    btw, how the relay usually works.
    the big green disc is an inrush limiter,
    when you plug the supply in that stops you getting a big spark at the switch/plug.
    then it heats up - to stop it burning up the relay then shorts across it because it's done it's job.

    Comment


      #3
      Re: OKI ES7411 Laser Color printer with 44201901YB power supply

      Thank you so much for your feedback, stj.

      So far, I started to desolder ALL capacitors and I measured both capacitance and ESR. All of them were perfect, however following your instructions I replaced these 3.

      Change of capacitors didn't cause any effect on printers situation, so I started to make comparisons between both SMPS.

      I realised several things:

      - The SMPS switches on the RELE when it has LOAD attached. So I guess that there is something that shorts a pair of pins (like an ATX SMPS) that tells the SMPS to switch on. Are there any schematics from this power supply???

      - The dead SMPS had an NPN transistor shorted (Q21) near the RELE. It has been impossible to see the model (even using the microscope), but I think it has labeled "BR" in it. I've replace it with a generic one 1AM (MMBT3904). That BR was a little bit bigger compared with the 1AM. Not sure how much it will last. Shout if this change has been a bad idea.

      After this change I have the DEAD printer WORKING.


      So now, I will follow up with the other printing.

      - For this one, the SMPS shorts the RELÉ and after a WHILE it opens it again. If I had to bet, I would say that the problem is on the SMPS and not in the LOAD. I could easily test it by replacing both SMPS and check whether I have a second printer working.....but not yet

      From the time being, I will follow up more or less same process:

      1- Removal of all capacitors and check both capacitance and ESR. This time if they are ok, I will not replace them........
      2- Check component level.....to see whether something is broken.
      3- If printer doesn't switch on, check first SMPS in the second printer.

      What could be the problem in a SMPS that switches on(activates relé) and 1-2 seconds later deactivates it?


      I will keep you updated,
      Francesc.
      Attached Files

      Comment


        #4
        Re: OKI ES7411 Laser Color printer with 44201901YB power supply

        While removing all CAPS to check capacitance and ESR (they all look ok), I realised that the Black-ebony inductor indeed it's a BURNT inductor

        I need to get glasses and pay more attention to details.........

        I have several questions on this topic:

        - Do the inductors break? (the inductor still has continuity)
        - Why it has turned black? Do I need to check any close component?
        - Is it worthy "now" to measure the inductance of the coil?
        - It seems that the "brown twin" that appears on the photo is the same. I could measure the inductance on this one and also count how many turns the coil has in comparison to the burnt one.

        Let me know your thoughts on this topic.



        Regards,
        Francesc.
        Attached Files

        Comment


          #5
          Re: OKI ES7411 Laser Color printer with 44201901YB power supply

          compare the inductance to the working one on the other psu - the heat may have effected the core.
          it has been overloaded - something on it's output-side may be shorted.
          something pretty big to do that type of damage!

          also, resolder every joint where the board is darkened.

          Comment


            #6
            Re: OKI ES7411 Laser Color printer with 44201901YB power supply

            Some follow up on this topic.

            I've done my first coil. I bought 1.3mm cooper and I've tried to do my best. I realised that using the old core was a bad idea.....burned cores doesn't give any inductance. I've recycled one core that is slightly bigger, but after 42 loops, I am reading about 120microH.



            PCB does the same...............switches on and switches off (relé sound).

            "Vertical PWM control board" works fine. I've switched both between power supplies.

            Next try is to change a pair of optocouplers. I've removed two of them to test them and I don't like the readings (they are PC3SF11). Let's see......

            Regards,
            Francesc.
            Attached Files
            Last edited by Francesc V.; 12-29-2022, 10:24 AM.

            Comment


              #7
              Re: OKI ES7411 Laser Color printer with 44201901YB power supply

              Final chapter of the story.

              - Changing optocouplers didn't make any difference.
              - Interchanging PWMs between PCBs neither

              However, after reviewing and reviewing it, and when I was about to give up and purchase a new power supply, I realised that next to the previously burned coild there were two tracks that were broken and continuity was lost there. It was obvious when seen throught microscope but not with the naked eye.......


              So, second Power supply is now working. I have rescued 2 laser color printers

              I am happy today

              Comment


                #8
                Re: OKI ES7411 Laser Color printer with 44201901YB power supply

                nice

                Comment


                  #9
                  Re: OKI ES7411 Laser Color printer with 44201901YB power supply

                  Hi,
                  I have the same printer with the 44201901 power unit, we turned it on this morning and an audible pop was heard from the power unit area and then no power to the printer. I've checked the 2 fuses with a multimeter and they appear fine but that is where my limited knowledge ends.
                  I've phoned OKI and they were as much use as a chocolate teaspoon telling me to send it to a 3rd party to supply and fit a whole new power supply.

                  would you happen to know anyone in the UK I could send the power unit to?
                  Or do you think it's easy enough for a novice like myself to take a look at and diagnose?
                  Thanks




                  Originally posted by Francesc V. View Post
                  Final chapter of the story.

                  - Changing optocouplers didn't make any difference.
                  - Interchanging PWMs between PCBs neither

                  However, after reviewing and reviewing it, and when I was about to give up and purchase a new power supply, I realised that next to the previously burned coild there were two tracks that were broken and continuity was lost there. It was obvious when seen throught microscope but not with the naked eye.......


                  So, second Power supply is now working. I have rescued 2 laser color printers

                  I am happy today

                  Comment


                    #10
                    Re: OKI ES7411 Laser Color printer with 44201901YB power supply

                    if you can solder and you have a meter then why not try to fix it?

                    start by posting pictures of both sides of the psu board.
                    if it made a pop then thats good because it probably left a mark of some kind to see.

                    Comment


                      #11
                      Re: OKI ES7411 Laser Color printer with 44201901YB power supply

                      Thank you for your assistance. Here are the 2 sides of my board.
                      What should I be looking for?


                      Originally posted by stj View Post
                      if you can solder and you have a meter then why not try to fix it?

                      start by posting pictures of both sides of the psu board.
                      if it made a pop then thats good because it probably left a mark of some kind to see.
                      Attached Files

                      Comment


                        #12
                        Re: OKI ES7411 Laser Color printer with 44201901YB power supply

                        Upon closer inspection I found this might have been what went pop
                        Attached Files

                        Comment


                          #13
                          Re: OKI ES7411 Laser Color printer with 44201901YB power supply

                          can you post higher res pictures of the top-side?
                          one of the optocouplers has a mark - maybe a hole in it!

                          Comment


                            #14
                            Re: OKI ES7411 Laser Color printer with 44201901YB power supply

                            that chip is 100% toasted!
                            i would also replace the 3 small caps below it and check the 2 diodes & film cap that got torched by it.

                            Comment


                              #15
                              Re: OKI ES7411 Laser Color printer with 44201901YB power supply

                              Is this image any better?

                              Originally posted by stj View Post
                              can you post higher res pictures of the top-side?
                              one of the optocouplers has a mark - maybe a hole in it!
                              Attached Files

                              Comment


                                #16
                                Re: OKI ES7411 Laser Color printer with 44201901YB power supply

                                ok, what i was seeing is somebody felt the need to wipe a pen across all the chips!

                                Comment


                                  #17
                                  Re: OKI ES7411 Laser Color printer with 44201901YB power supply

                                  It looks like the opto-coupler has blown and sprayed debris onto the cap.

                                  Comment


                                    #18
                                    Re: OKI ES7411 Laser Color printer with 44201901YB power supply

                                    BTW that mark is standard - I have the same board with the same mark but it still looks like it's toast.

                                    Comment


                                      #19
                                      Re: OKI ES7411 Laser Color printer with 44201901YB power supply

                                      IC9 doesn't look like an opto-coupler but a mosfet. Are you able to see the numbers on it or shall I disassemble my printer? Mine is MIP3E3S (see initial photos from the post).

                                      Regards,
                                      Francesc.
                                      Last edited by Francesc V.; 06-05-2023, 12:08 AM.

                                      Comment


                                        #20
                                        Re: OKI ES7411 Laser Color printer with 44201901YB power supply

                                        IC9 is likely a pwm controller ic with built in mosfet, post a clear picture of the ic or post the numbers that are printed on it, you may need to clean the ic with alcohol to read it.
                                        Last edited by R_J; 06-05-2023, 11:02 AM.

                                        Comment

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