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CM V700 no +5vsb, ICE2QR4765 low VCC in... Need guidance please...

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    #1

    CM V700 no +5vsb, ICE2QR4765 low VCC in... Need guidance please...

    Hello...

    I got my self a dead CM V700 PSU, with nothing on +5vsb

    I have tried to fix it for the past 2 week, and I'm stuck... so i guess i post it here to get some pointer before i scrap it..

    As you can see in photo, the psu still pretty clean, no visible damage or bulging cap.. when i got it, it still has CM seal on it

    The +5vsb system use ICE2QR4765, I have trace and measure the voltage on ICE2QR4765 and the only voltage reading i got is in VCC 4.8v, Drain 310v and FB 3v.

    I have read the datasheet and and still can not understand how it work...

    I believe the VCC should be higher, but after everything i done, still nothing

    Things i have done :

    Replace ICE2QR4765
    Replace the startup cap
    Remove and measure both snubber Diode and Vcc diode from Aux winding
    Remove and measure both CS resistor and ZC resistor
    Replace output cap
    Remove and measure output diode
    and everything was OK

    I believe the aux winding is responsible for creating VCC line for the ICE2QR4765

    I trace the vcc rail.. one goes to ICE2QR4765, to control board and to pfc area..
    I suspect that there is some kind of short that dragging the voltage down, and when i inject with 5v, got no load.

    I also suspect that the transformer is bad... when i measure the primary winding i got 1.90 Ohm, is it normal ? and .035 Ohm on Aux 0.22 on Sec

    when i measure the output, i got no voltage reading at all... and the output rail got no short.

    From my understanding, the +5vsb should be up first and the other will follow (CMIIW)


    So If anyone have any idea or suggestion on what i should do next, please advise...

    Thank you
    Attached Files
    Tags: None
    #2
    Re: CM V700 no +5vsb, ICE2QR4765 low VCC in... Need guidance please...

    Originally posted by mrcliem View Post
    I also suspect that the transformer is bad... when i measure the primary winding i got 1.90 Ohm, is it normal ? and .035 Ohm on Aux 0.22 on Sec
    Resistance measurement on an SMPS transformer usually won't show you any meaningful results, because there are way too few windings to show any DC resistance (which is what multimeters measure.) What you need is an inductance meter - one that can go down in the low uH range. The primary might measure something like 1-2 mH (100-200 uH), and the rest of the windings probably much lower due to having fewer turns.

    That said, I haven't seen the transformer go bad on the 5VSB on one of these PSUs with a dedicated offline PWM-FET IC like the ICE2QR4765, DM311, TOP-series, TNY-series, and etc. On 2-transistor self-osc. circuits, I have... but that's not the case here.

    I suggest disconnecting the APFC / main PWM controller from the primary aux. winding / Vcc of the ICE2Q IC and see if the 5VSB starts then. If not, you can try injecting a higher voltage (10-15V, or whatever the ICE2QR4765 takes normally) with an isolated power adapter while the PSU is plugged in. If the PSU still doesn't give 5VSB, then look into other components attached to the ICE2QR4765 IC. Perhaps you missed something like a tiny small ceramic cap shorted or similar?

    And if you really would rather fix the PSU than scarp it... and to me, this seems also more reasonable... then find a 5V 2-3 Amp power adapter and place its PCB inside the PSU to replace the 5VSB circuit. Just make sure to connect its primary aux. winding to the one of the PSU so that the main PS and APFC can work. It will be a bit of a Frankenstein, but still a way to get the PSU going agian.

    Comment

      #3
      Re: CM V700 no +5vsb, ICE2QR4765 low VCC in... Need guidance please...

      maybe test the transformer for any leakage between the windings
      when i watch diode-gone-wild pulling usb chargers apart, the biggest issue is the bottom of the transformer where the windings ofen touch or pass over each other!

      Comment

        #4
        Re: CM V700 no +5vsb, ICE2QR4765 low VCC in... Need guidance please...

        @momaka
        Unfortunately I don't have inductance meter, but
        I will try your idea of injecting VCC voltage on ICE2QR4765 and take another look on 5vsb circuit again..

        Well the reason for me to fix it, that this PSU will go to my son PC as he want to add a dedicated VGA card...and the one he have now just old non branded PSU

        @stj
        I have pull the transformer and measure the transformer, As I recall there is not any leakage between winding. But, I will try to pull everything on 5vsb circuit and measure it once again

        Maybe worth mentioning, with broken 5vsb circuit, when i plug the psu with wattmeter ( using my dmm in AC ammeter mode ), the psu still pulling .030 A on 230v AC.
        I suspect that the PFC circuit has not started yet without 5VSB...

        Well, I will try to look it once again, I will report back if I find some progress

        @momaka and @stj
        Thank you for your time to read and giving advise.
        Much appreciate it

        Comment

          #5
          Re: CM V700 no +5vsb, ICE2QR4765 low VCC in... Need guidance please...

          Originally posted by mrcliem View Post
          Maybe worth mentioning, with broken 5vsb circuit, when i plug the psu with wattmeter ( using my dmm in AC ammeter mode ), the psu still pulling .030 A on 230v AC.
          I suspect that the PFC circuit has not started yet without 5VSB...

          Well, I will try to look it once again, I will report back if I find some progress
          230v x 0.03A = 7 watt, that is quite allot, you could use a thermal camera to see what gets hot.
          "The one who says it cannot be done should never interrupt the one who is doing it."

          Comment

            #6
            Re: CM V700 no +5vsb, ICE2QR4765 low VCC in... Need guidance please...

            Originally posted by Per Hansson View Post
            230v x 0.03A = 7 watt, that is quite allot, you could use a thermal camera to see what gets hot.
            Thats what I thought too.. unfortunately I do not have thermal cam, and hand probing is a no no.

            I''ll try to trace the circuit again as soon i have some free time...

            Comment

              #7
              Re: CM V700 no +5vsb, ICE2QR4765 low VCC in... Need guidance please...

              unplug and hand-probe

              Comment

                #8
                Re: CM V700 no +5vsb, ICE2QR4765 low VCC in... Need guidance please...

                Originally posted by stj View Post
                unplug and hand-probe
                Well, discharge the main bulk capacitor before touching anything, including the heatsink!
                "The one who says it cannot be done should never interrupt the one who is doing it."

                Comment

                  #9
                  Re: CM V700 no +5vsb, ICE2QR4765 low VCC in... Need guidance please...

                  it may actually be the bulk-cap, i would touch the side and see if it's hot.

                  Comment

                    #10
                    Re: CM V700 no +5vsb, ICE2QR4765 low VCC in... Need guidance please...

                    mrcliem: just to be on the safe side please read this post in full before touching anything:
                    WARNING: Live heatsinks & single pole on/off switches in switching power supplies
                    "The one who says it cannot be done should never interrupt the one who is doing it."

                    Comment

                      #11
                      Re: CM V700 no +5vsb, ICE2QR4765 low VCC in... Need guidance please...

                      Sorry for late reply.. been busy for the last few days...

                      @Per Hansson.. Thank you for your concern, I already make sure to discharge the cap before I touch the board again.

                      Well.. today I have some free time, and since the new goal was looking that 6w pull... I decided to "cut" all the high voltage DC rail by pulling the component one by one..

                      As @stj suggested... I pulled the bulk cap... but still the same..

                      I started pull the resistor that feed 5vsb winding.. and goes to bulk cap, pfc diode and mosfet, gnd sense resistor and diode after the bridge rectifier..


                      I attached the picture with orange mark to show which component that i pulled

                      After all of that.. the board still pulling 6w...

                      I have double check all the point where usually have some voltage reading, and they all have no reading

                      I believe whats left are bridge rectifier, and some filtering cap...
                      I have not pull the bridge rectifier yet, as I measure in circuit that they still good...

                      I continue as soon I have some free time again...

                      Appreciate any advise...

                      Thank You
                      Attached Files

                      Comment

                        #12
                        Re: CM V700 no +5vsb, ICE2QR4765 low VCC in... Need guidance please...

                        Ok problem is probably that you are using an averaging multimeter, not True-RMS multimeter.
                        The film capacitors on the input will have very bad power factor.
                        So it is not possible to measure their true current draw without a true RMS multimeter...
                        You can try desoldering the X and Y film capacitors and see if I'm correct
                        Last edited by Per Hansson; 07-10-2023, 09:22 AM.
                        "The one who says it cannot be done should never interrupt the one who is doing it."

                        Comment

                          #13
                          Re: CM V700 no +5vsb, ICE2QR4765 low VCC in... Need guidance please...

                          It could be your 5vsb secondary circuit issue..the cold side. The dc 5v side.

                          Comment

                            #14
                            Re: CM V700 no +5vsb, ICE2QR4765 low VCC in... Need guidance please...

                            The ic's internal startup cell should charge the VCC cap to more than 4.8v on its own, I would expect it be charged to at least 10v, Is this VCC voltage the same with the original ic and the replacement?

                            Is ZD101 connected to the VCC pin?

                            The aux winding supplies the run vcc for the ice standby ic, but it may also supply a second vcc for a pfc ic etc.
                            Attached Files
                            Last edited by R_J; 08-25-2023, 09:30 PM.

                            Comment

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