Powered Speakers Failed -- Where to start diagnosis?

[Halcyon]

I have a pair of KRK "monitors" (speakers). They aren't anything particularly high-end but they have balanced inputs which I like and drive directly from my desktop. They are amplified internally (each has an IEC power input). A few days ago, I was using them, no issues. Powered them off when I was done and went to bed. When I went to use them the next day, BOTH had failed.

One makes an awful loud "screaming" sound the moment you power it up (even with no input connected). The other only has audio coming out of the tweeter (the woofer has no output at all).

Before moving house, I did used to just leave them powered on all the time, even at night.

I know they aren't proper studio monitors but I'd rather not just chuck them until they really die. What on earth could have gone wrong? Bad/Cheap/Under-rated caps maybe?

[HackedFridgeMagnet]

Have you tested with another Audio input?
Both failing at the same time, the only things common are the mains power and the Audio source.

Maybe a surge did some damage?
Can you open them up?

[Zero999]

Are they still within the warranty period? If so, then once you're sure they're faulty, return them to where ever you bought them from.

[alsetalokin4017]

Yes, first check your audio output to make sure you aren't feeding garbage to the speakers. From your description it doesn't sound like this is the case, but check anyway just to be sure.

Then open them up and carefully look at the boards for damaged capacitors, overheated resistors, etc.

There are a lot of threads on the internet about KRK speaker repairs. I haven't found one that talks about your exact problem but here's one where bad caps caused a problem:
http://forum.cakewalk.com/Shade-Tree-Repair-Guide-CracklingStatic-in-KRK-Rokit-6-Speakers-m3117829.aspx

Here's another repair page you might be interested in:
http://www.fivefish.net/diy/rp8/

[wraper]

One makes an awful loud "screaming" sound the moment you power it up (even with no input connected)

Might be something in the feedback loop (likely cap) or RC network from the output to GND. Depends on IC used. But of course check power voltages and bulging capacitors first.

[Halcyon]

Have you tested with another Audio input?

100% not the audio output. One speaker (the one with the noise) occurs with nothing connected at all to any input.

Are they still within the warranty period? If so, then once you're sure they're faulty, return them to where ever you bought them from.

Out of warranty I'm afraid. They are about 3 years old now.


Did a bit of Googling, a user on YouTube had similar issues. He replaced the caps. I haven't opened up my speakers yet, but if the caps are to blame, I may as well replace them all. What do I need to look for when replacing capacitors? Does voltage matter?

[Augustus]

But how likely is it that both speakers crapped out at the same time because of faulty caps? Was there a thunderstorm around your place last night?

[alsetalokin4017]

1.  Er... yes, capacitor voltage matters. Replace with same or (slightly) higher voltage rated capacitors of a good brand like Nichicon or Panasonic.
2.  The second link in my post above shows a lot of information that you might want to know, like how to open up the speakers, how to test amplifiers separately from the active filter board, etc. Even though his problem isn't the exact same as yours you still may want to look through that procedure.
3.  From that link and some others I found out that the tweeter and woofer have separate amplifier ICs. So if the woofer is out but tweeter still works on one speaker it may mean that the woofer amplifier IC needs replacing. (Guessing that your exact model speakers are similar to those in the threads I saw.) These are through-hole parts, common TDA amplifiers, so should be relatively easy to replace if they are bad.
4.  I see that several vendors stock replacement parts -- like complete amplifier boards -- for the KRK line of speakers.