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How to test an IC voltage regulator with a DVM

Discussion in 'Electronic Repair' started by LVMilkman, May 13, 2007.

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  1. LVMilkman

    LVMilkman Guest

    Is there a way to test an IC voltage regulator with a digital volt
    meter? I have a three pin adjustable voltage regulator and I need to
    know if it is bad.


  2. Guest

    If there are no shorts between pins (totally trashed), the usual
    method is to connect it up with the proper resistors and measure the
    actual output under varying loads. Is there any other way?

  3. Arfa Daily

    Arfa Daily Guest

    Not that I know of, and that is certainly the way that I do it. They are
    pretty reliable though, if we're talking something like an LM317T. I repair
    about 6 or 7 hundred per year of a particular board that uses one. I would
    guess that I get perhaps 10 regulator problems in that number, and amongst
    those, probably only 3 or 4 are the device itself. The rest are o/c
    resistors in the output voltage set chain, or short circuit caps at the set
    or output pins.

  4. Meat Plow

    Meat Plow Guest

    LOL pretty reliable and you repair that many?

    #1 Offishul Ruiner of Usenet, March 2007
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  5. I repaired over 10,000 CATV converters for United Video's Cincinnati,
    Ohio system in the early '80s, along with commercial C-band microwave
    receivers and other headend equipment for over a dozen CATV systems in a
    four year period. I processed the converters 100 at a time, unless the
    total spare stock was below that number and ran a production line
    repair, kicking out the few dogs to finish last.

    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
  6. Arfa Daily

    Arfa Daily Guest

    Hey Meat, how's it going?
    Perhaps you misunderstood what I said. I stated that I repaired 6 or 7
    hundred a year of a particular board that happens to *use* an LM317T. I then
    went on to explain that of those several hundred, *very few* of the faults
    that the boards had, were related to that '317.

    Actually, I've just looked at the figures, and I do about 100 every 6 weeks,
    so it's actually nearer 800 a year. This board has an LM317T and a 7805 on
    it, neither of which are heatsunk by anything other than being screwed down
    ( and often not very well ) to the PCB. Both of these regs run too hot to
    touch in normal use. I have a separate spares drawer cabinet for the repair
    of these, and in it, I keep a running stock of 5 LM317's, which I replenish
    perhaps once a year. The very occasional power supply faults that these
    boards suffer on their 12v rail, which the '317 is used to derive from the
    raw 24v supply, are almost invariably o/c surface mount R's in the voltage
    set network, or s/c tantalum surface mount caps.

    Considering that these devices are s/c, thermal, and SOA protected, this
    pretty much puts them outside being damaged by external conditions, so any
    failures have to be random chance. Semicon manufacturers have got random
    chance failures, after the bottom of the bathtub, licked these days, so I
    don't see why you find the fact that I don't have very much trouble with the
    317's, given the number that pass by me, funny ??

    Do you have some other experience of them ? Am I alone in not seeing a big
    reliability problem ? Just interested ... d;~}

  7. LVMilkman

    LVMilkman Guest

    Thanks for the help and I really appreciate the advice of the down
    stream resisitors. I will check all components, I just was not sure
    how to check a voltage regulator, but it seems that there is no easy
    way to do that with a DVM.

    Thanks again,

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