Need help to identify reason for high DC output voltage in power supply

Discussion in 'General Electronics Chat' started by sudha001, Feb 9, 2016.

  1. sudha001

    Thread Starter New Member

    Jan 8, 2016
    8
    1
    Recently my Sony Blueray player (BDP S-370) got busted due to high voltage. On opening the player, I found a faulty high voltage capacitor (400V, 100uF) in the power supply board, which I replaced with a new one. And before putting the board back into the unit, I checked the output voltages with a digital multimeter and found them to be higher than the rated values. The +12V output when tested with DMM shows +16.5V, which slowly reduces and stabilises around+14.6 V. The -6V output shows fluctuating values between -7.24V and -7.34V, while the +5.8V output fluctuates between +5.47V and 5.77V. My input voltage is 240V AC, and the output at the bridge rectifier is 336V DC, as tested using a DMM. I don't have much background in electronics and would appreciate your help in identifying any further faulty components in the power supply board.

    For reference the image of the power supply board is attached. It is a Sony APS-257 Board with part number 1-474-194-11. I could not find a schematic for the board in the internet.

    Thanks for your help.
     
  2. ScottWang

    Moderator

    Aug 23, 2012
    4,850
    767
    How are the those voltages after you replaced the 100uF/400V capacitor?
    Did you check the capacitors, does any capacitor is bulging?
    Does your DMM has any ESR function?
    ESR function was designed to measure the internal resistance of capacitor, sometimes when you using the DMM to measuring the capacitance of capacitor is quite normal, but when you using the ESR function to test it, the resistance could be less more than its normal condition.

    Capacitors bulging.
     
  3. RamaD

    Active Member

    Dec 4, 2009
    254
    33
    Many SMPS require a minimum load to have the output voltages within tolerance, so it may be alright, but I would still not connect them as the variation appears too much. The early ones (prehistoric) would blow without the minimum load. They have been improved. Since it is a OEM supply, the details may not be available. Try searching for maintenance / service manual.

    I could see 2 of these caps, and would recommend replacing both, as the other one would have also gone through the stress. Even otherwise, as it is not expensive, it is better to replace.
     
    Last edited: Feb 9, 2016
  4. sudha001

    Thread Starter New Member

    Jan 8, 2016
    8
    1
    The voltages I provided are after replacing the 100uF/400V capacitor, in fact I replaced both the high voltage filter capacitors to new ones, even though one looked good. All other capacitors look good under visual inspection, no bulging. I don't have a multimeter to test the capacitance function or ESR function.

    One more thing I forgot to mention in my original post is about the leakage current. When I use a tester to test the ground, there is a faint glow suggesting there is some current leakage. Also don't know what causes this.
     
  5. sudha001

    Thread Starter New Member

    Jan 8, 2016
    8
    1
    I was also thinking the same, but wanted to have some expert advice before connecting it to the load, as I don't want to screw up the main board. The 2 caps that you see in the picture are new ones, which I had fixed after removing the old ones. The slight dent in one of the capacitor is due to handling and not due to any damage while use in circuit. Thought that should not be a problem.

    I got the Blueray player service manual from internet, strangely, it excludes any details pertaining to the power board.
     
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