Announcement

Collapse
No announcement yet.

SMPS low Vout

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

    #21
    Re: SMPS low Vout

    You must mean C661 0.4v
    Is pin 4 of opto 5.2 volts measured to hot ground? If it is, the power supply must be trying to work and giving you that voltage, that means you should have something on +12, I would think at least 4-5 volts
    Could you be measuing those opto pins 3 & 4 wrong? reversed? The reason I ask is that the top247 should be outputing around +5 volts on its own

    You should also be getting more than .4 volts on C661
    If D662 is producing 5.2v. D661 should produce at least that much, Try removing one end of D661, Its only needed for the pfc circuit which is not working now anyway. With it removed, see if you get your +12v
    Last edited by R_J; 02-20-2019, 06:54 PM.

    Comment


      #22
      Re: SMPS low Vout

      Yes, right - c661 - 0.4V
      For the measures on the primary side I used for reference the negative pin of c661 ( I do not know if the term in English is "hot ground" ).
      I hooked the scope to the secondary side of the transformer and yes - something is going on ( see photo ), but still no voltage on the rails ( c707-0v, c708-0.07v, c709-0.15v )
      From the VPP on transformer pins 2 (0.22), 3(0.4) and 4(1) at least it seems that the secondary coils are fine.


      edit -
      Originally posted by R_J View Post
      ..Try removing one end of D661, ...With it removed, see if you get your +12v
      Please clarify - remove the diode and leave the trace empty, or remove the diode and shorten its pads?
      Attached Files
      Last edited by madan1; 02-20-2019, 07:19 PM.

      Comment


        #23
        Re: SMPS low Vout

        Yes, C661 negative is what we refer to as HOT ground.
        So pin 1 (C) of ic651 is only .46 volts? that can't be right

        Comment


          #24
          Re: SMPS low Vout

          Originally posted by R_J View Post
          Could you be measuing those opto pins 3 & 4 wrong? reversed? The reason I ask is that the top247 should be outputing around +5 volts on its own
          You are totally correct.
          Indeed the pins are reversed.. I got it wrong because on the schematics the IC pinout is mirrored.
          So on IC652.3 and IC651.1 there is 5.2V.
          On IC652.4 - 0.5V
          On c661 - 0.39V

          Comment


            #25
            Re: SMPS low Vout

            If you remove D661, that will eliminate any problem on the 20VPFC. The power supply will work with D661 removed (no shorting)
            This is such a simple circuit there is not much left, Maybe the transformer primary was damaged?

            Comment


              #26
              Re: SMPS low Vout

              With d661 removed:
              c661 - 0.07V
              ic651.1 & ic652.3 - 5.2V
              ic652.4 - 0.35v

              secondary side:
              c707 - 0.01v
              c708 - 0.05v
              c709 - 0.1v

              320v on the high V rail

              By the way, could a damaged transformer explain the exploded top247?

              Comment


                #27
                Re: SMPS low Vout

                Originally posted by madan1 View Post
                I will try to find one, but what do you think 0.1UM means ( quoted from the SM )? Is this 0.1uF? The cap is of the smallest smd type and is real pain in the a** to solder it in that overpacked space.
                Looks like 0.1 uF to me as well. If it's a tiny SMD ceramic cap, and you want to replace it with same, then get a dead PCI-E video card. The small ceramic caps near the PCI-E slot are always 100 nF (i.e. 0.1 uF), so those should work. Better yet, just get a 104 ceramic disc cap and use that instead. I'd say that cap is somewhat important, as the "C" pin of the TOP247 is used both for feedback and Vcc (and likely compensation?)

                Originally posted by madan1 View Post
                With d661 removed:
                c661 - 0.07V
                ic651.1 & ic652.3 - 5.2V
                ic652.4 - 0.35v
                With D661 removed, what voltage do you get on C663? This is the first filter cap for the TOP247 Vcc supply and feedback voltage.
                If nothing, check if diode D662 is good.

                You can also remove D662 and supply an external DC voltage at the cathode of D662 - and if you do, make sure your external DC supply is NOT ground-referenced, because you will need to connect its negative lead to HOT ground (i.e. connect the external DC supply across cap C663). 6-8V supply should do. Even 5V might work, but not 100% sure.

                Originally posted by madan1 View Post
                By the way, could a damaged transformer explain the exploded top247?
                Absolutely. Although it's more likely the other way around: TOP247 went bad and damaged transformer. But going by your readings, I doubt that transformer is bad. In general, transformer damage is extremely rare. I've personally only seen it on those 2-transistor flyback designs in cheap ATX PSUs. Never anywhere else.

                Comment


                  #28
                  Re: SMPS low Vout

                  Originally posted by momaka View Post
                  Looks like 0.1 uF to me as well. If it's a tiny SMD ceramic cap, and you want to replace it with same, then get a dead PCI-E video card. The small ceramic caps near the PCI-E slot are always 100 nF (i.e. 0.1 uF), so those should work. Better yet, just get a 104 ceramic disc cap and use that instead. I'd say that cap is somewhat important, as the "C" pin of the TOP247 is used both for feedback and Vcc (and likely compensation?)
                  I'll see if we have any of those cards in the office, but yes - it's one of the smallest smd ceramic caps.
                  Either way, I'll get one of those.. just probably will wait to collect a decent list of components to justify the trip to the shop.
                  Do you think that this cap might be the cause for the current problems?


                  Originally posted by momaka View Post
                  With D661 removed, what voltage do you get on C663? This is the first filter cap for the TOP247 Vcc supply and feedback voltage.
                  If nothing, check if diode D662 is good.
                  will check it next time and report


                  Originally posted by momaka View Post
                  You can also remove D662 and supply an external DC voltage at the cathode of D662 - and if you do, make sure your external DC supply is NOT ground-referenced, because you will need to connect its negative lead to HOT ground (i.e. connect the external DC supply across cap C663). 6-8V supply should do. Even 5V might work, but not 100% sure.
                  I guess a couple of li-ion batteries will do the job, right?
                  What is expected to happen with that injection?
                  Also, should I have the d661 back?

                  Comment


                    #29
                    Re: SMPS low Vout

                    You can reinstall D661 but the purpose of D661 is to provide the Vcc for the pfc circuit, this top247 circuit will operate just fine with the lower B+ voltage of 320 volts, so don't worry about the pfc circuit at this time. The fact that there is no real load on the 12,5,2.5 this supply should operate with the lower B+ supply to the top247
                    Last edited by R_J; 02-20-2019, 09:59 PM.

                    Comment


                      #30
                      Re: SMPS low Vout

                      Originally posted by madan1 View Post
                      Do you think that this cap might be the cause for the current problems?
                      Unlikely. But depending on the circuit design, it may be possible for the regulation to become unstable under very high or very low load. So if you can, do add it back in.

                      Originally posted by madan1 View Post
                      I guess a couple of li-ion batteries will do the job, right?
                      Probably. But I don't suggest using Li-Ion batteries in the circuit, because if something goes wrong, you certainly wouldn't want those to short-circuit or over-discharge.

                      Originally posted by madan1 View Post
                      What is expected to happen with that injection?
                      Essentially, what this does is it supplies a stable Vcc drive voltage to the TOP247 chip in order to rule out bad aux. primary-side winding on the transformer.

                      If inserting this voltage doesn't produce any voltage on the output of the power supply, there is something else wrong still. In which case, I suggest replacing the optocoupler and LM431 shunt regulator. In addition to that, make sure any resistors for the LM431 and optocoupler are not open-circuited.

                      Originally posted by madan1 View Post
                      Also, should I have the d661 back?
                      It doesn't really matter. D661 simply rectifies the 20VPFC supply, which is needed for the APFC. But at this point, we just want to make sure the TOP247 circuit works first. So D661 is irrelevant for the moment.

                      Comment


                        #31
                        Re: SMPS low Vout

                        Just got back to that PSU.

                        On ic651.1 - 5.27V
                        ic652.3 - 5.27v
                        ic652.4 - 0.47
                        c663 - 0.47
                        t651 between 9 and 10 - 0vDC and 0vAC(@50hz )
                        c661 - 0.36


                        by the way, what exactly is the logic of the optoc.?
                        When the psu is working fine, there should be constant V on the diode side, correct?
                        This should make the transistor side conductive, right?
                        What should be the normal working state of coil 9-10? I guess after the diode there should be some kind of a half-wave.. but should the RMS be higher or lower than the voltage of ic651.1 (~5v )? Also, does the ic651 expect high/low on pins 1 and 3 or reads the peaks of the half-wave?

                        Here are two shots of the scope.
                        the 0.2v one is from transformer pins 9 and 10
                        the 10mv one is from c663
                        Attached Files
                        Last edited by madan1; 02-24-2019, 03:45 PM.

                        Comment


                          #32
                          Re: SMPS low Vout

                          The optocoupler is there to provide regulation feedback, as the load on the 12volt or 2.5 volt lines change the voltage across the opto's led changes, this changes how the transistor conducts, varying the voltage from D662 to the ic's control pin.
                          What are you using for ground on that scope board? Like I said before I doubt it can measure 132Khz
                          The voltage on C663 will likely be around 7-10 volts when its working
                          Maybe you have a faulty to247 ic?

                          Comment


                            #33
                            Re: SMPS low Vout

                            I see, so even without any feedback from the optocoupler, the ic651 should be doing its thing?

                            For the c663, for ground I used the negative leg of c661 and pin 4 of the optocoupler, for the transformer, I hooked the probes directly to the transformer pins.
                            If I remember correctly, the scope is able to go up to 180-200kHz ( of course with signal generator and sine wave ).
                            Indeed this is the second top247 I bought. The first one was faulty, but later I noticed that probably I killed it, by applying too much solder which had reached through the board and shortened the top of the pins.
                            The funny thing is that the price of that ICs in that particular shop is like two times cheaper than in the rest ( of course not even close to the price in aliexpress ). So in the end it really could be a faulty IC... ( even though I never had issues with stuff bought from there ).

                            By the way, I got some strange readings on the diode side of the optocoupler.
                            R750
                            r751
                            r752
                            ^^ those were fine

                            r753 - code3321 / 1.2k in the schematics - measured 0.81k
                            r780 - code1201 / 1.2k in the schematics - measured 0.81k ( r780 and 753 are in parallel so I guess 0.81 is ok )

                            r754 - code1002 / 10k in the schematics - measured 0.89k ( in both directions ).. so is the resistor gone or ic750 is lowering its resistance?
                            Is there a way to test ic750 without getting it out of the board... the "best" thing is that I'll have to remove 3 other caps + probably a choke before the hot air gun can reach the resistors and the ic.
                            Last edited by madan1; 02-24-2019, 05:02 PM.

                            Comment


                              #34
                              Re: SMPS low Vout

                              The ic will do its thing for a few cycles but needs to see the run voltage from D662 to go into proper run mode.
                              I don't know about R754 but resistors rarely go down in value, the go high/open so it could be a bad ic, this ic is used on a lot of power supplies.
                              Looking at your scope display, It seems the top ic is in Auto-Restart mode
                              I guess that scope can measure up to 200khz so it should be ok for this

                              Re check the diodes in the secondary to make sure none are shorted.
                              Did you ever install the C653 0.1µf cap?
                              Last edited by R_J; 02-24-2019, 06:13 PM.

                              Comment


                                #35
                                Re: SMPS low Vout

                                Thanks for reminding me - just scrapped a cap from an old pci lan card. After I installed it, the V on c661 went down to 0.2v ( was 0.36 ) and on c663 - 0.3V ( was 0.47 ).

                                Just checked the diodes on the secondary.
                                d702 and d701 behave as expected.
                                zD703 starts leaking in the opposite direction after 1V ( 100ma@10V ) which I don't know if it is normal for that zener.


                                Do you know what is the "normal voltage" from d662?

                                Comment


                                  #36
                                  Re: SMPS low Vout

                                  D662 supplies the run voltage, it should be at least 7-10 volts
                                  If you can, disconnect D703, see if makes a difference.
                                  You could try shorting pins 3 & 4 of the optcoupler and see if the supply starts working, you just won't have any output regulation, butfor a test it should be fine

                                  Comment


                                    #37
                                    Re: SMPS low Vout

                                    Removing d703 did not make any change
                                    Shorting pins 3 and 4 on the optocoupler also did not change anything.


                                    I just injected ~6 and 8.2 volts on ground and ic651.1. Both times the voltage on pin1 went up to ~6.4 v, but still no secondary side V or 380V.
                                    On the 6V it consumed ~35ma both on and off. With 8.2v the draw was ~100ma on and off.

                                    Comment


                                      #38
                                      Re: SMPS low Vout

                                      Well there is not much left to check, I assume you already checked D6651 (should read open both ways) and D652. The top247 does'nt require much to work, so it leaves one thing, T651. If there are no shorts on any of the secondary outputs. I suspect either the primary winding or one of the secondary windings has a shorted turn. it only takes one turn to be shorted to kill the transformer, and you won't find that with a meter.

                                      Comment


                                        #39
                                        Re: SMPS low Vout

                                        Originally posted by R_J View Post
                                        Well there is not much left to check, I assume you already checked D6651 (should read open both ways) and D652. The top247 does'nt require much to work, so it leaves one thing, T651. If there are no shorts on any of the secondary outputs. I suspect either the primary winding or one of the secondary windings has a shorted turn. it only takes one turn to be shorted to kill the transformer, and you won't find that with a meter.
                                        I will check again the diodes and will also see if there is a way to temporary convert the board to manual on/off smps ( schematics for this top247 application could be found in its datasheet ).

                                        By the way, how to test the transformer?
                                        Here is what I have
                                        low voltage pulse generator 1hz-200khz
                                        several DMMs
                                        DIY scope
                                        DC power supply
                                        probably can scrap a 12v linear power supply ( remove the rectifier and use it as an AC power supply )
                                        DMM which can measure inductance
                                        "daylights module" ( mosfet 12Vin switching power supply with constant frequency and no filtering on the Vout ).

                                        Comment


                                          #40
                                          Re: SMPS low Vout

                                          You could disconnect the primary of the transformer and drive it with the pulse generator. You can first try this with just the primary disconnected (DON'T plug in the power supply) Connect the generator across pins 6 & 7 of T651. Vary the generator frequency close to 132khz. This setup will simulate the switching of the top247 and you might, see some voltage on the secondaries, or you might not due to the low output of the generator. The second option would be to completely remove the transformer and do the same and check the secondaries with the scope.
                                          You cant drive the transformer with 60hz ac, its ment for high frequency.
                                          Last edited by R_J; 02-25-2019, 12:43 PM.

                                          Comment

                                          Working...
                                          X