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Help with DMM Fluke 12B Cap Reading

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    #1

    Help with DMM Fluke 12B Cap Reading

    Hi all,

    I'm trying to troubleshoot a Phihong Switching power supply model PSM217-404-H-R for my Hanns G HD281 Monitor that's not turning on. I think that is one/some of the caps that are bad. I have a Fluke 12b Multimeter that I got a while back. I tested the capacitance on C601 and it registered 21.5 uF on the Fluke. The specs for this cap are 400v 22uF -- right on spec. I go and test C502 (25v 470uF) cap and get the reading of 3000-7900 uF's. Testing the other caps in the area return the same type of results. I am putting the Red Lead on the positive side and Black lead on the negative side (side with the off color stripe down the cap) using the capacitance setting. There are no bubbled/prego/leaking/brown stuff around the caps that would say their obviously bad.

    1. I would just like confirmation that i'm using this DMM right.
    2. What does this mean with the uF readings so high?

    C502 is the top right one with out the red marking on top. https://www.badcaps.net/forum/attach...7&d=1285542628

    -Jake
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    #2
    Re: Help with DMM Fluke 12B Cap Reading

    Originally posted by cyberndj View Post
    1. I would just like confirmation that i'm using this DMM right.
    Yes.

    The specs for this cap are 400v 22uF -- right on spec. I go and test C502 (25v 470uF) cap and get the reading of 3000-7900 uF's. Testing the other caps in the area return the same type of results.

    2. What does this mean with the uF readings so high?
    The caps are in parallel. When testing caps in circuit, you will not get accurate readings. You have to desolder them and test out of circuit.

    While the Fluke 12b can measure capacitance, it cannot (no multimeter can) measure ESR (equivalent series resistance).

    See this megathread on your monitor at

    https://www.badcaps.net/forum/showthread.php?t=11329

    I have come to a general conclusion that this particular monitor runs very hot and there are problems with the caps on both the power and main board. You can read through the above for all the details.
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    Comment

      #3
      Re: Help with DMM Fluke 12B Cap Reading

      Thanks for the Confirmation!

      I've been following that thread and going through the troubleshooting steps.
      +5v stand by - +4.95V check (Post 110)
      Voltages similar to post 119 and 121. - Check
      Unplug power, attach controller card and power switch to test as in Post 111

      then POP!!!!!! right when I plugged the power cord in.

      The path from JR1 to where the "negative end of the big cap in the middle connects" curled up and peeled off in parts. --See pic

      Is this repairable (solder a 23 guage wire from the JR1 to anotherpoint -- or am I screwed for this board?

      -Jake
      Attached Files

      Comment

        #4
        Re: Help with DMM Fluke 12B Cap Reading

        Originally posted by cyberndj View Post
        then POP!!!!!! right when I plugged the power cord in.
        Check your fuse, bridge rectifier and power mosfet.

        A good fuse should measure less than 1.0 ohms.

        Check bridge rectifier and power mosfet to see if they are shorted.

        Is this repairable (solder a 23 guage wire from the JR1 to anotherpoint -- or am I screwed for this board?
        See if there is continuity from the JR1 component to the cap. If not, then jumper it.
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        Comment

          #5
          Re: Help with DMM Fluke 12B Cap Reading

          Definitely something shorted if you can blow the whole track like that!
          "Tantalum for the brave, Solid Aluminium for the wise, Wet Electrolytic for the adventurous"
          -David VanHorn

          Comment

            #6
            Re: Help with DMM Fluke 12B Cap Reading

            Originally posted by Agent24 View Post
            Definitely something shorted if you can blow the whole track like that!
            Ya, i'm trying to figure that one out myself!

            If the fuse is the rectangular box in the picture, then yes its blown, no continuity across it. It reads "T4A 250V CQ" (4 amp fuse at 250V I assume). F1 is printed on the PCB and there is a burn mark right under it as well.

            Just want to make sure, but Points 1-4 is the bridge rectifier, 5-8 the MOSFEt and 9-10 the fuse?

            Thanks again!

            -Jake
            Attached Files

            Comment

              #7
              Re: Help with DMM Fluke 12B Cap Reading

              Yes, fuses are usually marked with Fx part designations, and the 'T4A 250V' confirms it.

              Points 5 through 8 is the bridge rectifier

              Points 1 through 4 look like a transformer.

              The MOSFET will probably be on the heatsink directly to the right of the mains filter capacitor (big 420v brown one) - I can see at least 4 devices attached to that heatsink, you'll need to trace the circuit and\or look up each part number and find out which one is correct.
              "Tantalum for the brave, Solid Aluminium for the wise, Wet Electrolytic for the adventurous"
              -David VanHorn

              Comment

                #8
                Re: Help with DMM Fluke 12B Cap Reading

                Yellow spray paint is your bridge rectifier. The pcb might say BD or BR.

                Blue spray paint might be your power fet. Green might be dual diodes.

                For all the above, you can test every possible pin combination in circuit. Any reading under 30 ohms suggests a short and requires you to verify out of circuit.

                For example, number the bridge rectifier pins 1, 2, 3, and 4. Measure the resistance between pins 1-2, 1-3, 1-4, 2-3, 2-4, and 3-4.

                PS. Remember that the heatsinks are "live" when power is applied. If you have to do board acrobatics to get a measurement, use cardboard for insulation. You could have shorted something and maybe that is why your power supply went pop?
                Attached Files
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                If you are new to this forum, we can help a lot more if you please post clear focused pictures (max resolution 2000x2000 and 2MB) of your boards using the manage attachments button so they are hosted here. Information and picture clarity compositions should look like this post.

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                Please do not post inline and offsite as they slow down the loading of pages.

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                Comment

                  #9
                  Re: Help with DMM Fluke 12B Cap Reading

                  Be sure to be aware of the capacitance range your meter can measure. If what you're measuring is below or above that range, your results won't be helpful.
                  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.
                  ****************************

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                    #10
                    Re: Help with DMM Fluke 12B Cap Reading

                    Just as a follow up. I ordered a replacement power supply and poped that one in. Now my screen powers on but the screen stays white and no menu comes up. So after reading up, it looks like that it is the T-Conn board might be bad.

                    ...Just FYI if anyone reads.

                    Comment

                      #11
                      Re: Help with DMM Fluke 12B Cap Reading

                      Originally posted by cyberndj View Post
                      Just as a follow up. I ordered a replacement power supply and poped that one in. Now my screen powers on but the screen stays white and no menu comes up. So after reading up, it looks like that it is the T-Conn board might be bad.

                      ...Just FYI if anyone reads.
                      There's often a fuse on the Tcon board (small surface mount) I'd check it.
                      36 Monitors, 3 TVs, 4 Laptops, 1 motherboard, 1 Printer, 1 iMac, 2 hard drive docks and one IP Phone repaired so far....

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