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Measuring forward bias on Motorola 962.3 diode rectifiers with multimeter

Discussion in 'General Electronics Discussion' started by ANA, Apr 4, 2018.

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  1. ANA

    ANA

    4
    0
    Apr 4, 2018
    I have 4 Motorola 962.3 Diode Rectifiers but no data sheet. They are fairly large black plastic diamond shapes with holes on either end for mounting screws and four leads. Two leads have yellow dots and a third has red and is the positive with the remaining one being the negative. I am not sure if these are bridge rectifiers or not. Would appreciate any information anyone has on specs. I only have a multimeter for measuring but it does have a diode function which I used. I am not a technician so bear with me. The reverse bias checked out ok on all four diode rectifiers as OL. When I measured forward bias with the black probe on the positive lead I noted on all four of the diode rectifiers the two yellow terminals had numbers in the .489-.493 volt range but when measuring the negative terminal it was in the .895-.890 volt range on all four.
    Why is that terminal different on all four and what does it mean in terms of determining if these components are good or bad?
    Thanks for any information or insight. ANA
     
  2. duke37

    duke37

    5,364
    772
    Jan 9, 2011
    Could you show a picture of the rectifiers and where you measured?

    I would suggest that you are measuring the forward voltage of one diode at 0.5V and two diodes in series at 0.9V.
    They are almost certainly bridge rectifiers but, if small, could be a ring modulators with the diodes connected head to tail.
     
  3. ANA

    ANA

    4
    0
    Apr 4, 2018
    DSC04698.jpg DSC04699.jpg
     
    Last edited: Apr 4, 2018
  4. ANA

    ANA

    4
    0
    Apr 4, 2018
    I have included a picture of the top and a side view. All 4 are the same so I just took pictures of the one. You can see the red dot which is positive, the two yellow dots where I measured the lower voltage drops, and the 4th one I considered negative as it is just black which is where the voltage drop was higher. The actual type is Motorola MDA 962-3. I did just find a data sheet. It it titled Rectfier Bridges. It shows the following:

    DC output volts Res. Load Volts 250 volts
    DC output volt Cap. Load Volts 400 volts
    Sine Wave RMS Voltage Line to Line Volts 140
    Peak Reverse Voltage per Cell DC or recurrent Volts 200
    DC Output Current @ 55 C Ambient Amps 10
    Peak Full WaveOne Cycle Surge Current Amps 250
    Peak Full Wave Recurrent forward Current Amps60
    So is it the design that causes the higher voltage drop on the negative lead so it is considered normal and the
    values are consistent with a functional diode rectifier?
    Thanks, ANA
     
  5. duke37

    duke37

    5,364
    772
    Jan 9, 2011
    I would think that the bridge is OK. Put a low voltage AC on the yellow connections and measure the output voltage on the black and red pins.

    The connections have been roughly soldered at some stage. Hopefully no damage has been incurred in the experiments.
     
  6. ANA

    ANA

    4
    0
    Apr 4, 2018
    OK. Thanks for all the information. It has been helpful! ANA
     
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