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    #1

    Checking fast recovery diode

    Got an unnamed LCD that uses Vestel 17ips16-3 PSU unit, making a very quiet clicking noise and wont come out of standby.

    I have located a diode in the PSU which I feel may be faulty, just want to run it by you guys before I order a replacement.

    It's a BA159 - a fast recovery diode datasheet at http://html.alldatasheet.com/html-pd...2/1/BA159.html
    and is D810 on the board if anyone is looking at a schematic.

    In one direction open circuit, other direction 5.9M Ohms both measurements taken out of circuit.

    This is faulty, right?

    Jim
    Tags: None
    #2
    Re: Checking fast recovery diode

    What type of meter (DMM/Analog) and what scale are you using to test?

    EDIT: Grabbed the diagram from elektrotanya.com for you.

    EDIT 2: <sigh> Sheet is for 17IPS16-1 or -2 not -3 as on their site...
    Attached Files
    Last edited by Toasty; 02-04-2012, 01:02 PM.
    veritas odium parit

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      #3
      Re: Checking fast recovery diode

      Looks like there are several of these on the board. Does this one differ from the others?
      veritas odium parit

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        #4
        Re: Checking fast recovery diode

        Haven't checked the others, good point i'll lift another and compare them. D801 and D803appear to be the same component. Will check against them.

        Comment

          #5
          Re: Checking fast recovery diode

          Originally posted by bbjunkie View Post
          In one direction open circuit, other direction 5.9M Ohms both measurements taken out of circuit.
          I normally use the diode test function to test diodes. A good diode should test between 0.5 and 0.8V one way and "out of range".
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            #6
            Re: Checking fast recovery diode

            Did this too, reading .440 or so (cant recall exactly, will re-test when im back in the workshop) but the extremely high resistance had me wondering.

            The whole reason I pulled it to test in the first place was that it was measuring 95k ohms in both directions in circuit.

            Comment

              #7
              Re: Checking fast recovery diode

              Ok, checked and D800 801 802 and 803 are in fact not the same. Perhaps this is one of the differences in the -3 version.

              There dont appear to be any other BA159 diodes on the board. In fact there are only 5 on the primary side, 4 rectifier diodes and the D810 which is in circuit with a few other components across pins 1 & 3 on the primary side.

              I will potter around some more with it and see how I get on. Any further problems and I will start a repair thread and post some pics.

              Comment

                #8
                Re: Checking fast recovery diode

                I don't think you're dealing with an open diode problem - a shorted diode would cause the symptoms described

                I've never seen a diode fail open, but I suppose it could happen.

                Bad SMPS controller, bad startup cap?
                Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
                For service manual, schematic, boardview (board view), datasheet, cad - use our search.

                Comment

                  #9
                  Re: Checking fast recovery diode

                  Diodes hould be checked using the diode checker function. An ohm meter can detect shorts or abnormally low resistance. But a healthy diode will usually read high resistance in the forward direction and extremely high or out of range in the reverse. An exception to that latter is that I have seen some schottkies read onthe order of 200 ohms in the forward direction. Different diode types have different forward voltages, which can be seen with a diode checker. Schottkies are usually low, .2V-.5V; regular GP diodes perhaps .5-.7V; FR and ultrafast perhaps .8-1.2V. I have seen highvoltage ultrafast parts as high as 1.5V.

                  Sounds to me like your power supply is in a burp-mode current limit state. That diode could be bad - that forwaard voltage sounds low to me, though different meters can read differently. Maybe check to see if the output is shorted by something in the load, or maybe a bad output filter capacitor.
                  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: Checking fast recovery diode

                    Ok, it has beaten me - i've started a repair thread: https://www.badcaps.net/forum/showth...463#post214463

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