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NAP110 Let the smoke out!

Yank

Yank

Bulbous Also Tapered
There was a lightening strike on my block today while I was at work. When I got home, I opened the door and immediately smelled ozone. Something electronic was fried. After sniffing around, I found the source - the NAP110 amp that I use for my TV sound (with an NAC42.5 and a pair of LS3/5As). I opened it up and this is what I found:

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There are fried resistors on both circuit boards, and two transistors that are visibly cracked and melted in Ch2 . I guess there must have been a voltage surge. The line fuse didn't blow, and the pilot light was still lit (I leave the amp on all the time, a practice which has now bit me in the ass).

I haven't tested anything yet, but I assume that the output transistors and drivers will all be toast. I wonder what, if anything, has survived...
 
Circled in red are components which are visibly failed; in yellow I've circled a couple that didn't burn up but appear to have been hot enough to sweat:

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Comparing to a NAP110 schematic, I'll open the floor to speculation on the current paths of destruction.

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Ouch! Are the LS3/5As ok?

PS One good reason I don't buy into the 'leave it on all the time' thing.
 
The output transistor with "CM" written on it is almost certainly gone to have fried those green wirewound resistors. Not looking too good for your speakers and also the Naim transformer may be cooked
 
It's neat that the transistors have actually exploded. If something's going to fail, let it fail spectacularly.

There are failed components in both channels in the SOA protection circuit. Which is impressive and DNBW.

Do you have a claim against the power company? Did anything else fry? Or does your home insurance cover this type of thing?

If the transformer has survived then perhaps LesW could supply some surplus Naim boards? That way you keep the amp original.

Paul
 
Yank, that is a b*gg**. You have my sympathy... Spectacular though!

I would not trust anything (apart from the small poly caps) even if it measures OK. Best to strip everything and rebuild using all new.
Only problem will be the burn, on the top board, from the bias resistors. Might find it has become 'conductive'?
Worse, maybe for the LS3s, is the blue speaker wire connector, which has also melted!!

Does your insurance cover this type of event at all?

Good luck.
 
Oooo I didn't spot that melted connection, looks like the speakers will have melted voice coils.

Pete
 
It's often easier and quicker to just relace the boards when this happens. And you may as well recap the power supply while you're at it.
 
The blue speaker wire isn't melted, that's a previous repair with white heat shrink.

I still find it odd that the line fuse didn't blow, and doubly odd because this is a UK amp that I converted to run on USA line voltage, and I never got around to replacing the line fuse with the proper value. The UK value is smaller. So I would expect it to have blown even quicker if something shorted and was pulling a lot of current.

I agree that at a minimum the boards will need to be shotgunned (just replace everything), or swapped out for known good ones. Anyone got a spare pair of 110 boards, maybe pulled from a 110 mono conversion?

If the power transformer is gone too, then the amp is a total loss, good only for the chassis and heat spreaders. The lightning strike was about 1:00 PM, I didn't get home 'til 4:30 so it sat that long turned on and blown.
 
I just checked and the woofers in both LS3/5As are toast.

These are Stirling "Repair Kit" LS3/5As with the Monacor woofers, so it's not quite so tragic a loss as if they had been vintage units.
 
Really sad to hear about this. Hope you manage to sort something with insurance and repairers and get some tunes back up soon. Good luck.
 
I'm not insured for this. I'm not lacking for tunes, this was a secondary system used only for TV.
 
Yank, I've got a couple of 140 boards somewhere. I think they may have some light modifications (SOA circuitry disabled, for example) but should be in working order. I'll go digging this evening.
 
Oh dear,

Very big bang.

That is what you'd normally consider a "beyond economic repair" situation.

Obviously on a DIY basis it's well within our repair capabilities but you're realistically looking at replacing pretty much every single component.

Bit of a pain!
 
IF the transformer has survived, the high value of old Naim kit still makes this a viable diy repair, as the parts are dirt cheap (accepting non-original output transistors), using the old pcb.
 
Ok, here's what I've got. A pair of 140 boards with a few of the standard mods:

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The mods:
  • Input cap is just a wire link (I can replace with tants, no worries)
  • Feedback cap is a Wima MKS2XL 22uF (I can replace with axial wet tants, much better)
  • SOA circuitry is gone
  • Critical resistors replaced with Welwyn RC55Y 0.1% tolerance parts
  • Output resistor replaced with a resistor//inductor combo as per Avondale
  • Front end power rails have been split from the output stage and decoupled with R/C, as per Avondale

If you'd like them I don't want anything for them, but a small donation to TonyL/pfm might be a nice gesture :)
 
I forgot to mention, the 42.5 preamp was powered from the 110, and its pilot LED was still lit, so at least power was at least getting that far.
 
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