How to figure out positive negative dc to dc converter

Hello,
I have a dc to dc converter for a computer. the unit uses 12VDC and put out 12/5 VDC. the coverter has no markings and none of the pins have continuity with the metal chasis.

can i determine the pos neg inputs using a digital multimeter?
6 answers Last reply
More about figure positive negative converter
  1. most decent multimeters will let you know if the polarity is reversed

    you do need a ground to check against the hots

    usually a black wire is a negative
    you should have a black on each output

    does is have white molex plastic 4 pin or black sata connectors?

    if it 4 pin molex that is easy

    (warning-disclaimer- I have 3 years of high school vocational AC/DC classes
    and trained at Lincoln Technical for HVAC- I AM NOT an electrical engineer :) )
  2. unfortunately this is a propiatary PSU. It is from a company called DATA911. the model is 7647 and it has a sigle molex connector with 16 pins. out of all the connectors three of them show zero ohms(I assume those are grounds). I have a Fluke 77/bn and it does show positive and neg resistance. Without a diagram can I find out which are the pos neg 12v input?

    Thanks for the help
  3. ok is this it
    http://auctions.findtarget.com/detail_product/370353019984/mds2000/

    if so here is support
    http://www.data911.com/support.html

    i tried about 5 googles searches and went thru about 10 pages of search results
    no luck on parts schematic

    I would try their customer support and if you ask nice
    and if you have a fax available they will probably send
    you a parts diagram

    also maybe could send to your email
  4. chiefaponte said:
    unfortunately this is a propiatary PSU. It is from a company called DATA911. the model is 7647 and it has a sigle molex connector with 16 pins. out of all the connectors three of them show zero ohms(I assume those are grounds). I have a Fluke 77/bn and it does show positive and neg resistance. Without a diagram can I find out which are the pos neg 12v input?

    Thanks for the help



    a ground to chassis would have minimal resistance
    measure voltage across the other wires to the ones that are thought to be grounds
    you want to set meter to VDC and range to 20v
    use black probe to ground
    red probe to possible hots
    usually the worst that can happen is you pop fuse on meter


    if you can open it up
    you can look where the connector joins the PCB board and sometimes they have very tiny markings
    of what the pin outs are
  5. Couple of points.
    (1) quote ...show positive and neg resistance.... End quote. No meter will measure negative resistance. If your meter shows a negative resistance then the line has a voltage on it and the reading is invalid.

    (2) the term ground, negative, and rtn get used alot. (a) the term negative and positive are relative terms meaning that one point (wire) is at a higher or lower potential than the other wire. Ground and negative - If the wire with the low potential is tied to ground then it becomes ground. Ground is more a reference point UNLESS it is tied to earth ground (Note Earth ground, chassie Ground, and referance point all have a different circuit sysmbol). If you have two wires, a return and a positive, if you want a positive out then the return is tied to ground, if you want a negative, you simply tie the positive to ground. Russian Satellites (and real old english cars) tie the positive of the battery to Ground and have a negative Vout, Just the opposite of the norm.

    The pins that show the highest number of wires "shorted" together (zero ohms) should be the return side, also refered to as common. Simply connect black DVM lead to one, then measure all the rest with the Red lead, then label your drawing showing the pin-out.

    Fuse in Meter is only inline when measuring current. And does not matter what range you are on, if the meter is set to current and you put it across the voltage lines, you will blow the fuse, I know - I've done that a couple of times.

    Fluke makes some very good DVM, I have the 85-III @ home and use the 87-V at work.
  6. a "negative" to chassis would have minimal resistance
    measure voltage across the other wires to the ones that are thought to be grounds
    you want to set meter to VDC and range to 20v
    use black probe to ground
    red probe to possible hots
    usually the worst that can happen is you pop fuse on meter


    if you can open it up
    you can look where the connector joins the PCB board and sometimes they have very tiny markings
    of what the pin outs are


    @ Retired Chief

    I think I said the same thing you did LOL
    to quote
    The pins that show the highest number of wires "shorted" together (zero ohms) should be the return side, also refered to as common. Simply connect black DVM lead to one, then measure all the rest with the Red lead, then label your drawing showing the pin-out.

    so set meter to VDC at a range of 20VDC
    then use black probe on the pins though to be ground (or common)(the ones with no resistance to chassis since most devices use negative for a common excluding Russian satellites and old Jaguars)
    then use red probe to measure hopefully voltage from the other "hot" or "positive"
    pins

    should be either + 5v or + 12v on those pins

    though me personally I would contact manafacurer and have them
    fax or email me pin-out of the 16 pin connector
    Pretend to be a contractor who needs schematics for state contract or something
    like that
    government agencies always want schematics for installs
    the Data911 MDS 2000 was used in many police vehicles from which
    that power supply was used for
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