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Old 17th July 2006, 03:56 AM   #1
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Question Power supply capacitor grenaded

I was driving to a lake yesterday, listening music... Then I heard a LOUD bang... it was firearms grade loud I continued driving, all my tires seems to be fine, amp was playing great. Today amp just died, fuses blown... Opened it: power supply capacitor ("+" wing of power supply) looks like a flower On same wing of power supply one mosfet shorted. Replaced both.
What can cause a capacitor to blow so dramatically (50v, 1000mF)?
Can a blown capacitor lead to mosfet failure? Or is it likely some other problem affecting both components? Thank you!
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Old 17th July 2006, 05:32 AM   #2
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A friends amp did that,because the input voltage was a tad too high (~15V) blew a 35V cap into "confetti" all over the inside of the amp,luckily nothing else was damaged at all,only had to replace the PSU caps.(Did them both,why not.)
In a regulated amp,this shouldn't be the cause.(unless the regulation has stopped working correctly.)

Other causes are maybe heat,age,excessive ripple,etc..
But,you might want to check your alternator voltage just to be on the safe side.
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Old 18th July 2006, 01:23 AM   #3
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If that capacitor is on the secondary side of the supply, check the rectifiers. If one leg of the dual rectifier breaks, it can cause excessive ripple when the amp is driven hard.
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Old 18th July 2006, 03:44 AM   #4
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Ah, the joy of unregulated supplies .

Another thing that happens often is the leg(s) on cap(s) and coil(s) can break off and cause some very intresting problems. Check all caps by slightly rocking them back and forth and see if one of them moves a lot.

Also, a common thing is to have bulging, puffy caps. If you see any, replace them.
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Old 18th July 2006, 12:53 PM   #5
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Default takes a licking and keeps on ticking.

I'm working on an amp now that had a loose solder joint on a cap, almost like it was a cold joint. Sometimes I think we forget about the vibration aspect and what it can do. the electronics sure take a beating it seems to me, it's a wonder they last as long as they do.
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Old 18th July 2006, 03:08 PM   #6
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Thank you for all the ideas!!! I Really appreciate your help.
About the amp: replaced cap. together with shorted FET, cranked it up at low volume... 2 minutes... BAM... 4x20 AMP fuses gone
That's one more shorted FET for sure. So I guess something else is messed up in power supply

P.S. That's the same Audiobahn amp that had FET's overheating in power supply without any load, and I am still unable to fix it . It worked amazing for a week, and I run it VERY hard. 494 working, drivers are great, all resistors are fine, zeiners ok, rectifiers ok. I don't have a schematics, but I can see that there are 2 leads from power suplly to an amp section that are possibly used for some sort of control (duty cycle, as function of load?), may be something wrong here
I am going to buy a scope today
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Old 18th July 2006, 04:44 PM   #7
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Are the power supply FETs still overheating?

If so, when you get the scope, post photos of the waveforms on the gate of both banks of FETs (one image per bank) and the waveforms on pins 9 and 10.

If you're not familiar with scope settings, set the vertical amplifier to 5 volts/division. Set the timebase to ~5us (you want ~2-3 pulses to be displayed).
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