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Thread: not getting +5v or +3.3v

  1. #1
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    not getting +5v or +3.3v

    I'm not getting +5v or +3.3v from my Sproggy PSU. I thought I was, but I'm not now. I have about 8 wires coming from the +5v section, is this too many to handle?

    I have replaced one of the 787s with a 788 to see if I could get +3.3v but I got something like +7v.

    All the other outputs are fine. What could have gone wrong, which bits could be bad??? How can I test this more?

  2. #2
    FLAC mp3z24's Avatar
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    test it without anything attached to the wires.

    what do you get on the rails with no load?

    ~mike
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  3. #3
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    I'll have to try that tonight, but the only thing connected to the wires is the LCD.

    Would having all those connections make the output different?

    (I know little about electrics)

  4. #4
    FLAC mp3z24's Avatar
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    test it with a multimeter....make sure that none of the voltage wires are touching the ground wires. you should probably disconnect your lcd until you make sure you are outputting the correct voltages... you dont want to find out that your voltages are too high by frying your lcd.

    just having the empty leads soldered on will do nothing. there is nowhere for the electricity on the un-connected wires.

    also, regardless of the number of wires attached, you will get your maximum voltage at each output. current is what will be variable, it is dependent on the current demanded by the various "things" that are connected by the wires. if the things are demanding too much current, then most likely, some of them will not work. but your voltage reading will stay the same.

    ~mike
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  5. #5
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    I've double checked everything and the outer +5/3.3v output is outputting +5v fine, but the other isn't.

    When I swapped the two MAX787s around the outside +5/3.3v still worked, but the inner didn't.

    I used a Multimeter to check the voltage throughout the circuit and the only difference is between the MAX787 and the MBR745. Could the MBR745 or the 47uH inductor be my problem?

    (note: I used an audible tester on the MBR745s. One that worked did not bleep, the one I think is faulty did bleep continuously).

    I think I'm almost there but just need a little tip from you kind people.

  6. #6
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    make sure that the MBR745 is not the Heat sink.... with 787/ 788

  7. #7
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    Originally posted by Mastero
    make sure that the MBR745 is not the Heat sink.... with 787/ 788
    It is using the same heatsink, does that matter???

  8. #8
    jol
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    Originally posted by mkkbb


    It is using the same heatsink, does that matter???
    yes, you cannot use the same ground, there is two ic's that has to be electrically insulated, check this post

    the first three posts are ok, ignore the rest.

  9. #9
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    remove the heat sink and check the voltage.....

    and isolate the mbr745from the heat sink

  10. #10
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    All the ICs are insulated.

    I have one big heatsink for MAX787, MBR745 and the LM2587T-12. Each one is insulated and has the plastic gromits for the screws.

    Could anything else be wrong???

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