Williams Defender power board C6 firework

mantisgamer

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While testing voltages on the power board, capacitor C6 blew (see picture). I'm hoping someone can contribute their experience and/or expertise to give me an idea as to what caused C6 to blow.

+5v measured at +7.05v
Unreg +12v measured at +7.3v
Unreg -12v measured at -39.4v
Reg +12v measured at +12.26v

dd95f55ad4e203d0610224a3652b6d43.jpg
 
Not certain what caused that cap to blow. Usually they blow when installed backwards or reverse voltage applied. I'm not certain how you were testing your voltages but I am just guessing that perhaps your probe touched an adjacent trace and sent positive voltage to the negative side of the cap. ....or...the cap just decided it was time to fail in a spectacular way. Definitely time for a rebuild either way.
 
C6 is your -12V filter cap and is rated at 1000uF, 25V. But you see nearly -40V on that one. You exceeded the operating voltage of the cap resulting in the sights, sounds and smells that you experienced.

Don't replace caps until you figure out why you are getting -39.4 volts on the -12V line.
 
C6 is your -12V filter cap and is rated at 1000uF, 25V. But you see nearly -40V on that one. You exceeded the operating voltage of the cap resulting in the sights, sounds and smells that you experienced.



Don't replace caps until you figure out why you are getting -39.4 volts on the -12V line.



Thanks. I'm about to desolder and check all components. Time consuming but you're right. I don't want to blow a new cap. I can't even imagine how I was getting so much voltage though... I'll figure it out.
 
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