Beware of NAD M3 Fire Hazard

https://ibb.co/T1VBM5G

I’ve never seen the top vent of an electrolytic cap blown off like the one in the photo.

That’s just plain scary!



heaudio123 Said:

Could be anything, but a shorted diode in the bridge passing AC and cooking the capacitor would be my guess.

Wouldn’t that cause a high current load on the secondary winding of the toroid power transformer causing the primary winding to overload and cause the 5 amp (I assume a slow blow) fuse to blow?

.

ok... you probably got a simple case of defective cap.... most likely there is no more damage to the the unit . you need all 4 caps to be replaced and that is probably it ...  

@heaudio123, thank you for your response to my post. I know you are extremely knowledgeable about such matters, and my relevant design experience dates back a few decades.

I would be interested, though, in your comments about the section entitled "Operating Lifetime Model" on page 13 of the following Cornell Dubilier "Aluminum Electrolytic Capacitor Application Guide":

https://www.cde.com/resources/catalogs/AEappGUIDE.pdf

Based on the equations shown there it appears to me that operating such a capacitor at 50% of rated voltage would double "expected operating lifetime" compared to operating it at 90% of rated voltage, which to a close approximation is what is done in the M3.

Regards,
-- Al

I'd recommend, seriously, this time, not attempting to put resources into repairing it; When the electrolytic off-gassed and spewed its internal magic smoke, conductive fluid (electrolyte) went all over the other parts (IC's in particular) making new instantaneous conductive pathways and likely altering the nominal set points; It's any ones guess about the future reliability.

From a practical point of view, how relaxed would any of us be if the amp IS reworked? I sure as heck would not be able to enjoy music with this refurbished amp. I would be on edge...wondering when the next magic smoke makes an appearance;

It would be wonderful if NAD would pick up the tab on a proper failure analysis and next steps; 

BTW, I had an M3 in 2006 and really liked it; Very smooth and neutral; Beautiful to look at too; Impressive chassis design.