weird and very frustrating story here.
 
bought a pro condenser mic (AKG C414 XLS, ~€1000) via mail order in the UK. lasted one month. then all the sudden developed a very high noise floor like the vocalist would be standing a strong see breeze.
 
sent it back. got it fixed.
 
lasted a year, then same problem. this time back to AKG repair center in Vienna who fixed it and confirmed it is not a chinese clone.
 
lasted a year, broken again. back to AKG Vienna for another fix.
 
now just yesterday. after 3 weeks vacation turned on phantom power and there is the sea breeze again. the mic worked perfectly for 2 years before vacation. I had left it plugged to the same preamp, just covered it. the studio was locked and physically taken off the main power (i.e. 380V mains unplugged) while I was away. so definitely no mechanical impact, no power surge.
 
yet all by itself the mic does not work. none of my other mics (irrespective of price) ever did anything like that. the tech who fixed it twice is no longer answering that email ... so now I need to go searching for the right person to fix that again ...
 
 
anyone of guys familiar enough with the internals of these mics to explain any plausible reason for this always happening?
 
 

Found this over at GS, and sounds similar.

https://www.gearslutz.com...14-b-xls-problems.html

Since condenser mic's require phantom power, I would look at that as a potential cause.  Have you been using the same phantom power source on the mic's that went bad?

I think it's a fair analogy that most people will think that because something is produced in China, no love or effort is put into the production. Being a fan of AKG headphones - K271 Mk.2, K702 and really want to get the 812's one day ....
 
Never realised there was an Inverness also in Florida.

fireberd
Since condenser mic's require phantom power, I would look at that as a potential cause.  Have you been using the same phantom power source on the mic's that went bad?

It's only been the same single mic and it has always been used with a UA LA-610 MK II which BTW I have used with Neumann mics for years without any problems (also doubled checked yesterday when I found the AKG C414 again broken, I went to the Neumann and it was fine a always)
 

interpolated
I think it's a fair analogy that most people will think that because something is produced in China, no love or effort is put into the production. Being a fan of AKG headphones - K271 Mk.2, K702 and really want to get the 812's one day ....

Same here with headphones. I believe AKG pro stuff is still assembled and quality controlled in Europe ... plus they used to have a "cloned product" warning on their homepage. Hence, when the mic went bad first time after a single use, I thought I had bought a replica (which it is not) ...
 
 

Well, it was a thought.  Being a tech I think of those types of things.

I'm sorry for your trouble. I have the same Mic.

I have had issues with pre amps before.

I'm thinking hard about your issue because I don't want it. I'm wondering about the switches for pattern and pad. Humidity? Smoke? Temperature? Idk, but it sounds like something in your environment is causing the problem. The pre amp is the most obvious thing.

Have you tried a different pre? My Neumanns don't have electronic switches in them.

Sorry to hear about this.  
 
FWIW, I've owned two C414-XLS mics for the better part of 10 years.
Never had a problem with them.
Used them with numerous mic preamps (Neve, Neve clones, UA 610, etc)

What did they do to "fix" it? Did they give you an idea?  Sounds like a ticking time bomb to me, like they are fixing the symptom but not the cause.  I would guess something like a faulty power filtering capacitor is slowly frying a transistor or IC in the audio circuit.  Let the problem go on too long and they are bound to pop.  Only replacing the transistor will not cut it.  Then again, a bad phantom power supply in the preamp could cause the problem too.  You should use a multi meter to check if you are getting a clean 48 volts from the preamp.

A multimeter won't really show how good the DC signal is.  An Oscilloscope is the best way to tell how good the DC is.