Power supply issue

Discussion in 'General Electronics Chat' started by rumburaski, Jun 13, 2013.

  1. rumburaski

    Thread Starter New Member

    Jun 13, 2013
    1
    0
    My RCA DRC8335 DVD/VCR COMBO Power supply is hot. I cannot touch the rectifier diode on the heat sink. I have replaced a couple of blown electrolytics including the 2200uf one. Now the combo runs but with issues. For example, the power supply runs scorching hot. The hottest spot being the rectifier diode mbr on the heat sink, just behind the 2200uf electrolytic that bursted (not shown, already replaced). Also the unit continues to display "finalizing" on the screen after dvd burning, even if the finalized disc is ok. To get rid of the "finalize" i have to turn the unit off and let it cool for five minutes. It is challenging for me because i don't have a schematic. Are any of the diodes failing under load or something else? Here are some pics.

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  2. Shagas

    Active Member

    May 13, 2013
    802
    74
    Maybe your electrolytic burst because there is a problem with the rectifying bridge/diodes .
    Try taking them out and testing them
     
  3. t06afre

    AAC Fanatic!

    May 11, 2009
    5,939
    1,222
    Collateral damage it not uncommon in such cases
     
  4. Evil Lurker

    Member

    Aug 25, 2011
    117
    23
    Which caps did you replace and what with? I see the one Nichicon cap, can't get a good look at the series but I'm thinking its a VZ series since as far as I know they don't make HZ series in that voltage range. If it is a VZ series then it needs to be swapped back out because it is not appropriate for the application in which you are using it. VZ series is a high temp standard capacitor one step above VX or VY. For the output filter cap of a SMPS you need something with lower ESR and more ripple current handling capability like a PW series or possibly HD.

    Also in my experience on SMPS where you have been hit with "bad caps" typically you find more than one that has failed, quite often without any visible symptoms such as bulging or leaking, simply the ESR has gone so high that they are no longer functioning. This can cause your feedback loop to go haywire in (addition to using the wrong replacement cap series). I recommend a total recap job.

    Also while your at it, I have found that it can save quite a bit of time if you just go ahead and replace all the zener diodes while you are in there. Its quite probable that they are OK, but if you have one go flaky they can be a real bear to try and troubleshoot.
     
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