White rubbery material on circuit board

Discussion in 'The Projects Forum' started by ascetic, Jun 16, 2012.

  1. ascetic

    Thread Starter New Member

    Jun 16, 2012
    I have a satellite receiver that used to work perfectly but suddenly stopped turning on today. Although usually these sort of problems are attributed to power connection, I figured I would open up the box to see if there were any noticeable problems inside. Everything on the circuit board looks fine other than this white rubbery material around the radial capacitor that I'm not familiar with. After doing a bit of research most people were describing this material to be either used in order to reduce vibrations on the capacitor or as a glue to help hold the heavier capacitors in place. So I was just hoping if someone more experienced than I am could confirm whether this is the silicone sealant/glue mentioned above or if it's a bad capacitor. Thanks in advance.
  2. paulktreg

    Distinguished Member

    Jun 2, 2008
    It's silicone sealant (or similar) used for exactly the reasons you state. You commonly see it on switched mode power supply components.
  3. wayneh


    Sep 9, 2010
    In the upper right of the photo, the PCB seems to show signs of heat, maybe excessive heat. You may want to look at that area more closely.
  4. KMoffett

    AAC Fanatic!

    Dec 19, 2007
    Took me a while to find the browned plastic insulation on the near edge of the ribbon cable, not the PCB. Looks like it might have been sitting against the heat sink.

  5. Evil Lurker


    Aug 25, 2011
    I would say there is a 90% probability that the filtering caps on the output are kaput. Been there, seen them too many times. Those cheap chinese caps fail all the time with no visible outward signs... what happens is the ESR starts to creep up which causes the caps to heat, the heat causes the ESR to degrade further, so on and so forth causing a chain reaction till the caps can no longer maintain the correct output voltage. Usually what will happen then (if your lucky) is an IC on the board picks up on the low voltage and will cause the device not to boot (satellite receivers are basically computers after all).
  6. ascetic

    Thread Starter New Member

    Jun 16, 2012
    Thanks for the help. I'll have to check for overheating and the filtering caps next time I get a chance.