B&W ASW610 subwoofer burned out twice now

One of my two B&W ASW610 subwoofers last year experienced a circuit board overheat and burned out.  The fuse didn't protect the unit from whatever caused the burn out.  I use a PS Audio power cord into a PS Audio Power Port so I know it's not that.  My dealer ordered in a new circuit board from B&W and replaced it at their store.  All was well until just now today. I upgraded the cable today and when i went to unplug the unit, the circuit board burned again.  The odor was very strong and I know it's not the fuse. The unit is dead.  I have a mind to toss it out in the garbage but for what it's worth, anyone have any ideas as to why this subwoofer would burn out twice and my other ASW610 operates perfectly.  Same system, same room, they're both about the same age, etc.  It is a lemon?  What am I doing wrong?
Its not you. You've done nothing wrong. If it can be fixed again under warranty do that and sell it. If not then no point throwing good money after bad. But no point throwing the sub out either. Not when it can still be used as a perfectly good passive sub.

Go somewhere like PartsExpress.com find the Dayton sub amp, find a nice sub kit. Get 3 now, or however many you can afford. Always can add more later. The more you get, the better it will be. But even two or three will be massively better than what you had. And a lot more reliable.
class d amps tend to have high and sudden failure rates. meaning when they go, they go all of a sudden, and the ’when’ part is like a clock. They all (of a given model) tend to go/pop/fail around the same age of overall time/hours of use and thermal accumulation. They will seem to perform perfect until that moment comes.

So we get a lot of that ’my class d amps are perfect and don’t fail, not the slightest sign of a problem’.

Then... they pop... all of a sudden. And most tend to be tricky fixes.

so it’s a great deal for the companies who add class d products into their amplifier portfolio. No repair, just earth/planet disposal abuse, tied to their selling you something new, like clockwork. All while looking like the good, or at least innocent guys, with their earth saving efficient class d amplifiers. Which would be true if they weren’t all scrapped due to some simple design flaws that could likely be fixed for about $5 spent at cost. It’s all about the money, as people shop by price..and..they just don’t know or understand the complexities of the technology.

I’ve personally seen somewhere near 8 of those B&W asw amps popped and one of them got fixed. and it’s not like B&W wants them to fail, either.

It just that some of the components, the internal parts... of class d designs  -are stressed to the limit. This is how they operate, it is their very nature. Think of 1000lb rated ropes being used constantly near or at their 1000lb limit. The failure rate will naturally be high. Same for class d plate amps. Works perfectly until it doesn’t.

As for the rest...a few were converted with a new plate amp, about half were scrapped. Parts express is the place to shop for a new plate amp for them. In one case, I supplied a class a/b mirage brand sub plate amp for the person to use instead. They thought the sub sounded just as good afterward.

Point is, the Mirage brand Canadian made old school class a/b sub plate amp was almost 20 years old and is still performing perfectly. I expect somewhere near ZERO (regularly used) class-D plate amps to survive that long.
I heard that Class-D amps have to work extra hard with smaller drivers (like your 10 incher). A bigger cone more efficiently produces the low frequencies so you amp has an easier load. 
So every powered sub I know of uses Class D amps and they tend to be more reliable than this.

Wait, the failure occurred at the same time you removed the plug from the wall?
There is a weird condition that happens in switching power supplies, not the amps.

The issue has to do with very short term power interruptions, in the neighborhood of 1-2 cycles of AC power, though by now I would not expect this issue to remain in professional devices. The issue is that the very short interruption causes the normally switched output transistors to turn linear. When they turn linear, they loose their 80-ish % efficiencies and turn 30-ish % efficiencies. In other words, they convert a lot more power to heat and burn themselves out.
I wonder if this is what the OP had?
Thanks folks.  All excellent feedback in particular how class D amps just fail out of the blue.  Makes sense.  It was 5 years old.  Actually I recalled my steps and it didn't occur when I pulled plug out of the wall.  My error.  I had removed the interconnect cable from the back of my surround sound processor and that's when it blew.  Now the sub was in standby mode and the processor was off.  This is when the board burned up.  The sub was still plugged into the wall but it was still a sudden short term signal interruption.   Lesson learned I guess.  I went ahead and purchased a new one yesterday.  I can use it as a passive sub as millercarbon suggested above.
OP - Don't get me wrong. That condition I mentioned is STILL very much a bad, or incomplete design, and it's just supposition.

It could be anything.

But yes, you can replace the amp with a nice Class D with a DSP front end, giving you expanded capabilities. :)
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