Announcement

Collapse
No announcement yet.

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

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

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

    Rescued this one
    Started it up in the computer case, and noticed that it would shut down after about 10s in the BIOS
    Took it out, connected to hard drive and it loses all power on all rails (except for 5VSB) after about 40s or so. (the same result happens without a hard drive connected)
    The 5VSB drops to 2.5V when it 'shuts down'
    And the voltage across the primary cap falls from 335V to 330V at the same moment
    I think that the 5VSB is regulated by an A6069H PWM chip (which was initially dropping to 2.5V even before the the PS-ON was grounded - but it now stays at 5V if the PSU isn't started)

    It has a CM6800 APFC chip.
    I thought about bypassing it, to see if it was the culprit, but it looks too complicated to do after looking at the application circuit that's pictured in the PDF.

    Monitoring Vcc on the A6069H PWM standby(?) chip:
    11V when PSU is first switched on,
    then jumps to 18.6V when PS-ON is grounded,
    then falls to 9.63V when PSU shuts down after about 40s

    Any experience/thoughts as to what might be causing this phenomena?
    Last edited by socketa; 12-20-2022, 03:43 AM.

    #2
    Re: Zalman ZM500-GV stops after 40s and 5VSB drops to 2.5V

    Your PFC isn't working if you only get 335V on the main filter cap. 230x1.414=325.22

    Comment


      #3
      Re: Zalman ZM500-GV stops after 40s and 5VSB drops to 2.5V

      it's 240V mains here
      240V X 1.414 = 339V, which is close enough to 335V

      what voltage should i expect to see across the primary cap?

      Comment


        #4
        Re: Zalman ZM500-GV stops after 40s and 5VSB drops to 2.5V

        Probably around 390V.

        Is the 5VSB stable during the ~40 seconds it is the correct voltage? If it is bouncing around (but the average is 5V) and the standby regulator also provides housekeeping power then that might cause the PFC IC to not operate.
        PeteS in CA

        Power Supplies should be boring: No loud noises, no bright flashes, and no bad smells.
        ****************************
        To kill personal responsibility, initiative or success, punish it by taxing it. To encourage irresponsibility, improvidence, dependence and failure, reward it by subsidizing it.
        ****************************

        Comment


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

          Yep, the 5VSB is very stable: 4.99V to 5.00V
          Would there be an issue if i disconnected the APFC mosfets and the diode to try to bypass the APFC, as it's a combination APFC/PWM chip?
          I guess that a next step would be to check Vcc of CM6800
          Last edited by socketa; 12-20-2022, 05:29 PM.

          Comment


            #6
            Re: Zalman ZM500-GV stops after 40s and 5VSB drops to 2.5V

            Read the datasheet of the cm6800 carefully. Also read the PFC over volt protection section.. Sounds very similar to the problem what you got. In any case fix the PFC and hopefully everything will be fine.

            Comment


              #7
              Re: Zalman ZM500-GV stops after 40s and 5VSB drops to 2.5V

              OK thanks.
              i'll see what's happening with voltage the at the Vfb pin, and will post back any findings here.

              I checked the voltage of Vcc of cm600:
              It settles to around 390V when PSU is plugged in
              when the PS-ON is grounded it falls to 13.9V (which is about what it's supposed to operate at, according to the datasheet)
              then when the PSU shuts down the main rails, it goes to 230V and works it's way up to about 360V
              all that i can gather from that is that the chip is being powered and possibly doing something with it.

              Comment


                #8
                Re: Zalman ZM500-GV stops after 40s and 5VSB drops to 2.5V

                From the datasheet:
                A resistor divider from the high voltage DC output of the PFC is fed to VFB. When the voltage on VFB exceeds 2.75V, the PFC output driver is shut down.
                Voltage at Vfb is constant at 2.52V, and after about one and a half minutes, the fan cuts out and the Vfb voltage drops right off - so, unfortunately, it doesn't look like there is an over volt protection event causing the PSU to shutdown

                Comment


                  #9
                  Re: Zalman ZM500-GV stops after 40s and 5VSB drops to 2.5V

                  It was an example how the cm6800 works. It could be anything else too like OVC.
                  After all, the PFC actually does work and is nothing wrong with it. If there would be something wrong with the PFC itself it wouldn’t turn on period. Does this thing have a supervisor ic?

                  Comment


                    #10
                    Re: Zalman ZM500-GV stops after 40s and 5VSB drops to 2.5V

                    Ok, fair enough
                    yes, it has a PS229 4-Channel secondary monitoring IC on the secondary side.

                    Comment


                      #11
                      Re: Zalman ZM500-GV stops after 40s and 5VSB drops to 2.5V

                      i observed the three voltage rails (as well as the current protection and voltage protection pins of the PS229 chip) - and no sudden voltage changes before the PSU shuts down,
                      Also checked Vcc (it's powered by 12V - not 5V as in the typical application schematic)

                      Comment


                        #12
                        Re: Zalman ZM500-GV stops after 40s and 5VSB drops to 2.5V

                        Check the FPO pin. If it goes high the PS229 is shutting everything down.

                        Comment


                          #13
                          Re: Zalman ZM500-GV stops after 40s and 5VSB drops to 2.5V

                          FPO remains at 44mV, right up until PSU fan cuts out
                          at the moment that the fan cuts out, it drops to 0V
                          and then it rises, and sits at 1.9V
                          so it doesn't look like that that's responsible for shutting everything down, since the shutting down happens before it goes to 1.9V
                          Last edited by socketa; 12-21-2022, 07:23 PM.

                          Comment


                            #14
                            Re: Zalman ZM500-GV stops after 40s and 5VSB drops to 2.5V

                            Oh boy…that thing need some serious TLC! I guess one has to sit down and draw a schematic of it or find a schematic. Then go from there. The cm6800 needs minimum 10v to operate. Funny thing that you get 11v to start with, but ends up with 9.6v at shutdown. It should be stable at 11v with it being off. Same thing with the voltage at the input filter cap. That should be always your ac mains voltage x 1.414. Usually VCC is taken from the rectified ac mains voltage, going through a bunch of resistor a capacitor and then to the chip. All I can think of is either the cm6800 is putting a load on, or a resistor gets higher in resistance value (happens to me once), thus starving the cm6800 voltage on the VCC pin.

                            Comment


                              #15
                              Re: Zalman ZM500-GV stops after 40s and 5VSB drops to 2.5V

                              The cm6800 needs minimum 10v to operate. Funny thing that you get 11v to start with, but ends up with 9.6v at shutdown
                              Those are the readings for the A6069H PWM chip, not the cm6800 chip (see post #1)
                              CM6800 readings are in post #7
                              Also, i'm assuming that it's OK/expected to have 390V (with only standby on), or 360V (when the PSU 'shuts down' to 2.5V standby) sitting on the CM6800 Vcc pin - because that hasn't blown it up yet.

                              i'm getting close to disconnecting the PFC mosfets, and bridge the boost diode, to hopefully get lucky and maybe sectionalize the problem
                              Last edited by socketa; 12-22-2022, 05:59 PM.

                              Comment


                                #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.

                                Comment


                                  #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.

                                  Comment


                                    #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.

                                    Comment


                                      #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.

                                      Comment


                                        #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

                                        Working...
                                        X