len-35
Level 1 (0 points)

Q: How to test a recapped LC SWM power supply?

I got my LC working with a replacement power supply two weeks ago. Found a couple of leaky caps and some corrosion on the PWB. Replaced all the caps and cleaned up the corrosion. (Note: This PS measured normal voltages before being removed from the LC but evidently could not provide enough current to power up the hard drive, [generating a ticking sound instead]). Any way, I know that testing of SWM PS's on the bench

is different from linear PS's and advice as to the proper method would be appreciated.

Len-35

iOS 6.0.2

Posted on Feb 8, 2014 11:05 AM

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len-35

Q: How to test a recapped LC SWM power supply?

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  • by Jan Hedlund,Helpful

    Jan Hedlund Jan Hedlund Feb 8, 2014 2:08 PM in response to len-35
    Level 6 (9,901 points)
    Feb 8, 2014 2:08 PM in response to len-35

    Hi Len,

     

    Sorry, cannot provide you with a proper method for testing this power supply, only a couple of general comments (although all this is probably known to you already).

     

    A regulated power supply (switched or not) should ideally maintain an almost constant voltage (for each output pin) over the entire load range. However, without access to details or specifications, it is wise not to test a PSU without a load.

     

    You should find the output voltages (+5 V, -5 V and +12 V) and their respective maximum currents (in A) on a label on the PSU. In principle, one could of course calculate resistor values needed to create various load situations for each output, and then measure the output voltages, but these resistors must be high-power units and therefore not always available. Appropriate incandescent light bulbs may be used as substitutes under certain circumstances, but it is very important to take into account the much lower filament resistance when cold.

     

    Jan

  • by len-35,

    len-35 len-35 Feb 8, 2014 2:38 PM in response to Jan Hedlund
    Level 1 (0 points)
    Feb 8, 2014 2:38 PM in response to Jan Hedlund

    Hi Jan,

    Good to hear from you. I think resistors might be better then light bulbs for the reasons you stated.

    Thanks for your input.

    Len

  • by Appaloosa mac man,

    Appaloosa mac man Appaloosa mac man Feb 8, 2014 8:19 PM in response to len-35
    Level 5 (4,330 points)
    Feb 8, 2014 8:19 PM in response to len-35

    I do not want to talk you out of repairing a power supply but if you are anywhere near a large city - like Seattle - you should be able to find a recycling company that processes e-waste.  They will have surplus power supplies.  Let us know if you are near Washington state.  Besides having a good football team, go seahawks, the state has a lot of resources for ecycling.

  • by len-35,

    len-35 len-35 Feb 9, 2014 7:00 PM in response to len-35
    Level 1 (0 points)
    Feb 9, 2014 7:00 PM in response to len-35

    I haven't put power to my LC PS yet because I decided to replace the two caps in the front part (HV section) of the PS. I'm having a problem finding a large HV cap of the same or smaller dimensions (30.2 mm dia. x 25.4 mm high). It's a 180 mF @ 385 V.

    There is also a 8.2 mF @ 50 V cap but my question concerns the value; is the 8.2 mF critical? I've got some caps that are 10 mF but is 8.2 mF necessary for correct operation?

    Any advice?

    Len