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I've got some active studio monitors (powered speakers). Last night, quite happily listening away, and all of a sudden the right one goes 'POP' followed by a steady low hum and no music. The cone is also 'sucked in' and only relaxes when I turn them off.
Today I got it open and whipped out the power supply board. Can't see anything obvious/burnt stuff etc.
Any ideas? Not happy 🙁
"Sucked in" means that only DC power is getting to the electromagnet, where it requires AC power- the program material to make a sound.
Does it smell? if it is a driver problem, then it's likely to be the varnish used for insulation on the coils melting and no longer functioning properly - this has a pretty distinctive smell.
Other than that, the humming suggests the amplifier is working, so it's potentially either then driver or the cross over. Do you have a spare driver (not the one from the other one - if it is a problem, then you don't want to kill that to.) you could try that in it's place and see how it goes.
What make are they? - perhaps drop the manufacturer an email explaining the problem.
One of my KRK VXT 6 Active speakers developed a background hum from the Amp circuit and KRK replaced the entire speaker foc despite it being 3+ years old.
I did notice a smell when I opened it up. But then that could've just been cos it'd never been opened. I'll have a look round for an old driver to check. They're bi-amped, no sound from either driver at all, apart from the loud electrical hum.
They're Samson Rubicon R6A's but I've had them years, bought second hand too.
long time since I did any electronics (it was my degree but never used it since) - could it be an electrolytic capacitor that went pop? any obvious signs of liquid on the circuit board?
No, first thing I looked for. I don't really know what I'm doing, but I've always had a go at fixing my own stuff. Had a few successes and I learn something every time.
*One of the first things I learned was the perils of not discharging big caps 😯
There will be a resistor/capacitor network in the cross over which will be prior to the amplifier in a bi-amped system, and could well cause the symptoms above.
I'll have another look.
Suggest the output link capacitor has failed shorted, allowing the amplifiers output bias voltage through to the driver coil (and causing the speak to get "sucked" in.
Measure the voltage across the driver it should be 0v when measured with a meter set to DC mode (i.e. it should average 0v) if it has a dc offset, there's your problem.
Don't leave the unit on for too long as this DC offset may kill the driver or the amp! (if it hasn't already done so)
Work back from the speaker driver output and find the set of (bigish) caps in series with the output line, switch off, power down caps (best to ensure 0v by "shorting" with a low value resistor), and measure the series resistance of those caps
Thanks for that. I'll have another crack later on.
Yeah, I turned it off straight away, and only had it on for a couple of seconds since. I'm hoping it'll be good.