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Zalman ZM500-GV stops after 40s and 5VSB drops to 2.5V

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    #16
    Re: Zalman ZM500-GV stops after 40s and 5VSB drops to 2.5V

    Check the opto isolator secondary side. Probe both pins to secondary gnd.
    Last edited by CapLeaker; 12-22-2022, 06:32 PM.

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      #17
      Re: Zalman ZM500-GV stops after 40s and 5VSB drops to 2.5V

      There is three opto isolators in a row on this PSU,
      One of them is the following:

      According to that application circuit schematic there is an opto isolator connected directly to the VDC pin of CM6800
      i located it, and verified, that that is the same in this PSU.
      On the other side of that particular opto isolator i measured resistance of both pins to secondary ground
      results are:
      8K and 2.8K

      Or should i probe for voltage instead?
      Last edited by socketa; 12-22-2022, 07:22 PM.

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        #18
        Re: Zalman ZM500-GV stops after 40s and 5VSB drops to 2.5V

        Check the voltages on those pins. It would be much easier to have a schematic. Matter effect, check all them opto isolators. Once when the psu works ok and then again when it shuts down.
        I assume you recover / restart the psu by temporarily unplugging the PSon pin ?
        Last edited by CapLeaker; 12-22-2022, 09:11 PM.

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          #19
          Re: Zalman ZM500-GV stops after 40s and 5VSB drops to 2.5V

          In tandem with these events: just standby/ps-on grounded/psu shuts down:

          The voltage that's on one pin goes from 0V to 7.9V to 0V
          The voltage that's on the pin next to that goes from 0V to 6.8V to 0v

          And (for the sake of completeness) the voltage that's on the pin that's connected to the cm6800 PWM voltage feedback input pin goes from 0V to 1.9V to 0V
          Last edited by socketa; 12-22-2022, 09:31 PM.

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            #20
            Re: Zalman ZM500-GV stops after 40s and 5VSB drops to 2.5V

            Hmm. So between these 2 pins there is only a 1.1v difference when on?

            Comment

              #21
              Re: Zalman ZM500-GV stops after 40s and 5VSB drops to 2.5V

              Hmm. So between these 2 pins there is only a 1.1v difference when on?
              Yes, that's correct
              Last edited by socketa; 12-22-2022, 10:16 PM.

              Comment

                #22
                Re: Zalman ZM500-GV stops after 40s and 5VSB drops to 2.5V

                PC123
                Type Long Creepage Distance Photocoupler
                Forward voltage typical: 1.2V

                Comment

                  #23
                  Re: Zalman ZM500-GV stops after 40s and 5VSB drops to 2.5V

                  Boy, that’s right on the threshold. And that’s the opto that goes to the cm6800, I expected more voltage difference than that.

                  Comment

                    #24
                    Re: Zalman ZM500-GV stops after 40s and 5VSB drops to 2.5V

                    OK thanks,
                    I'll swap it with another one from another random parts PSU, and will measure the voltage again, and see if it makes any difference.
                    Will post results here

                    Comment

                      #25
                      Re: Zalman ZM500-GV stops after 40s and 5VSB drops to 2.5V

                      i don't think it is the opto. Could be, but me thinking its not.

                      Comment

                        #26
                        Re: Zalman ZM500-GV stops after 40s and 5VSB drops to 2.5V

                        i swapped it with an Everlight EL187 opto, which, according to the datasheet, has a typical forward voltage of 1.2V.
                        the difference between the pins on the secondary (when PS-ON is grounded) is now 1.03V (9.82 - 8.78)
                        when i turned it on for the fist time with the replaced opto, it wouldn't start, because the standby was at 2.5V already
                        after a few more attempts, standby is now 5V for at least 30 seconds, but it was dropping to 2.5V, like before (initially), without me doing anything
                        and like before, after about 30 seconds of powering on the PSU, it shuts down, and standby drops to 2.5V

                        The fact that it didn't behave normally when i first plugged it in (standby was already 2.5V) would mean that it's not the APFC chip?
                        Or would a faulty APFC/PWM chip/circuit affect the standby supply even when the PSU is not powered up?
                        It does seem like the chip is doing something in standby mode, since (as you previously mentioned) that's what the CM6800 OVP protection part does (makes standby go to 2.5V)

                        I notice that there is no MOVs installed on this PSU - maybe there was a voltage spike that screwed up the chip?
                        Last edited by socketa; 12-25-2022, 02:51 AM.

                        Comment

                          #27
                          Re: Zalman ZM500-GV stops after 40s and 5VSB drops to 2.5V

                          Usually the stdby on these cm6800 or FAN4800 have a separate 5VSB circuit, likely using an TNY277 IC or something similar. When the power is off the cm6800 shouldn't do anything at all. Post a straight shot high resolution picture.

                          Comment

                            #28
                            Re: Zalman ZM500-GV stops after 40s and 5VSB drops to 2.5V

                            A6069H PWM 7-Pin chip is on the primary side - frontside of board
                            PS229 4-Channel secondary monitoring IC is on the secondary side - frontside of board
                            CM6800 is on the backside of the board
                            and it does has a MOV, but not an NTC thermistor


                            Attached Files
                            Last edited by socketa; 12-25-2022, 02:43 PM.

                            Comment

                              #29
                              Re: Zalman ZM500-GV stops after 40s and 5VSB drops to 2.5V

                              Check replace those 5 caps near the heat sinks.

                              Comment

                                #30
                                Re: Zalman ZM500-GV stops after 40s and 5VSB drops to 2.5V

                                i checked the four caps on the primary;
                                the bigger one (Taicon PW 220uf 50V), that's next to the 7-pin chip, capacitance is good, but the ESR is very low when i first connect it to the ESR Meter: 0.000 ohms
                                i guess that that means that it's not a good test
                                i'm having a fossick to see if i can find a replacement.

                                Comment

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