My $3k NAD M3 started shooting sparks out the top and burned the shelf that was 8" above. Luckily I was home and not sleeping or the house would have burned down. If anyone has one of these I advise them to unplug it when not in use. I took it to two different repair shops and they said it would be about $800 to just get it running and there may be board issues. They advised not to take the gamble. Anyone have any suggestions on what to do with it?
I bought the unit used 3 year ago on AudiogonThe unit was never left on when not in useThe local line voltage is 110 A cd had finished playing 20 minutes earlier and I hadn't turned off the components yet. I was in another room when I heard the noise and ran in and saw the sparks shooting out the top. The room was filled with smoke. Another minute and the house would have been on fire. Very alarming and scary. I will try to contact NAD.
Thank you everyone for the useful information. I guess I will just have to take the loss and move on. I will never purchase an NAD product again. Anyone have a recommendation for a good integrated under 2k. It’s for a second system driving Merlin tsm-mmm speakers. Thanks.
pwb,
I wish you would take the time and contact NAD tech support here in the US. Send them the photos you provided on this thread. The photos speak volumes to the damage that was caused by the cap in the amp. Make sure you tell them the sparks were still flying when you walked into the room. Let them know if you had not been home there is no telling what the damage may have been to your home. Be polite! .....
I would hope NAD America would want the amp to determine exactly, if possible, what caused the catastrophic event that caused the electrolytic cap to blow its’ top the way it did. I would hope NAD America would pay for the shipping.
NAD has made millions of units with very high reliability and excellent sonics for very reasonable prices.
NAD are well engineered. Electronics are made of component sourced from dozens of manufacturers. A dozen or more maybe involved in the power supply alone. All are potential points of failure for which NAD unjustly suffers the blame.
It's possible that a line surge coupled with a weakish part at precisely the wrong moment caused the only catastrophic failure on the planet.
The probability than another NAD unit would suffer a similar fate is small.
The unit is an audio computer and computers are replaced quite frequently.
The last firmware update was a decade ago, so the unit could be nearing EOL.
Some questions: - did you buy it new? - was the unit left on all the time? - what is the local line voltage?
I noticed the vent cap on the other cap did not look like it was affected by the event. It doesn’t look like there is any bulging in the top vent cover. Wouldn’t the shorting diode have affected that cap as well?
@jea48 Jim, good question, but the answer is that the schematic shows that there is a separate diode bridge (and other circuitry) associated with each of the two capacitors that are in each channel. One set of diodes/capacitors/and other circuitry provides approximately +72 VDC, while the other set provides approximately -72 VDC.
Best regards, -- Al
Al, thanks for the quick response. You provided the reason why.....
Any thoughts on my comment on this part of my previous post.
heaudio123,
Would you please explain the event in time of the shorted diode. How long of an event time did the short of the diode last before, I assume, the diode blew apart breaking the short circuit on the secondary winding of the toroid power transformer?
I haven’t seen capacitor application notes in decades, but I believe heat still applies, right? That is, the capacitor can be aged while on, not necessarily because of the voltage applied but because of the heat in the amp. Further, higher temperature caps also have longer life spans at a given temperature than lower temp caps, or am I mistaken?
I agree, unfortunately, that the failure here seems not worth fixing. That’s a lot of cleaning to do, with no guarantees.
If it were MY personal unit, I would attempt to clean it, and see if the remaining power supply works, and if the logic/preamp circuits appear in tact, then and only then would I attempt to rebuild the burned out side. Still, lots of work with no guaranteed happy ending.
I noticed the vent cap on the other cap did not look like it was affected by the event. It doesn't look like there is any bulging in the top vent cover. Wouldn't the shorting diode have affected that cap as well?
@jea48 Jim, good question, but the answer is that the schematic shows that there is a separate diode bridge (and other circuitry) associated with each of the two capacitors that are in each channel. One set of diodes/capacitors/and other circuitry provides approximately +72 VDC, while the other set provides approximately -72 VDC.
Could be anything, but a shorted diode in the bridge passing AC and cooking the capacitor would be my guess.
jea48 response: 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?
No it would not blow the fuse. The capacitor is not a dead short when reverse biased, but a low enough resistance that it will heat quickly and blow up.
heaudio123, Thank you for your response. I think I understand what you are saying in your above statement. The cap had a lot of stored energy and it was suddenly fed with a reversed polarity by the shorting diode. Kind of like connecting two 12Vdc car batteries in parallel out of polarity with one another.
I noticed the vent cap on the other cap did not look like it was affected by the event. It doesn’t look like there is any bulging in the top vent cover. Wouldn’t the shorting diode have affected that cap as well?
Could be anything, but a shorted diode in the bridge passing AC and cooking the capacitor would be my guess.
heaudio123,
Would you please explain the event in time of the shorted diode. How long of an event time did the short of the diode last before, I assume, the diode blew apart breaking the short circuit on the secondary winding of the toroid power transformer?
Thank you everyone for the useful information. I guess I will just have to take the loss and move on. I will never purchase an NAD product again. Anyone have a recommendation for a good integrated under 2k. It’s for a second system driving Merlin tsm-mmm speakers. Thanks.
As an authorized NAD servicer for over 40 years this is the first time I’ve heard of this. I can’t see how this would occur UNLESS the user keeps their electronics on all of the time. The user did not mention they were listening the time it failed, so I guess they do keep it on at all times. In standby, the capacitor that failed is not in the circuit. If powered to a fully on condition, the capacitor is live and before any regulation. If there are issues with incoming AC power they will translate thru to these 4 capacitors. If the user does not keep the unit on at all times this can still occur, but it’s less of an issue. Capacitors can and do fail due to many reasons but there is nothing endemic in this model. If the incoming AC power is above the nominal voltage (typ. 114-126) for long periods of time, this can put a stress on filter caps in pre-regulated circuits. Here is a good suggestion for all electronics... do not place anything combustible above the equipment and the "burning" component will not have anything to ignite. I do agree with the poster directly above this as the highly corrosive electrolyte is likely spewed onto many parts and the PC board, too. It will cause metal component leads as well as. PCB traces to corrode and fail. Also, the unit uses double sided PC boards and many small "plate-throughs" (micro rivets that connect one side of the board to the other) that are easily damaged from the electrolyte.
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.
@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":
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.
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 ...
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?
My old tech friends refer to the dead NAD as a boat anchor. We use to play golf with am/fm Delcoes in the late 70's, you will need a good sludge hammer. Very sad to hear of your plight, glad you were home. I always consider NAD as a really good brand-I have no experience with their equipment. My good buddy Chrisopher Coffin, superb audio tech, had this to say about fuses. A 200 picture tube will blow and save the life of a 25 cent fuse(1979). Not quite his original saying, but you get the drift.
Looking at the service manual again that capacitor is a 22,000 uF 80 volt polarized aluminum electrolytic. As can be expected it is connected to the output of a diode-based full wave rectifier. But based on what you (pwb) were told it sounds like something else failed in the power supply which caused that cap to explode. If so, that something else could have been a lot of things, as there are a great many parts in that circuit.
However, although the schematic is a little hard to interpret I’m fairly certain that the DC voltage appearing across that capacitor in normal operation (and across the other three similar capacitors, each channel having two of them, one for a + voltage and one for a - voltage) is between 70 and 74 volts. If so, that seems to me to be a failure waiting to happen, as a cap should be run at a voltage that is much less than its rating, IMO. Preferably at something like half of the rating.
Al, that amp has a lot crap in it! How long did it take for you to find the 3 fuses?
Not long, Jim. The service manual includes a block diagram, a schematic, and a parts list. Which made it pretty easy to determine what fuses are being used, and where they are located in the circuitry.
And a quick look at rear panel photos that are available on the web confirmed that the fuses are not physically located on the panel.
Al, that amp has a lot crap in it! How long did it take for you to find the 3 fuses?
pwb said:
I took it to the NAD authorized repair facility and they said a faulty power supply caused the round cylinder ( not sure of part name) to explode
round cylinder in the power supply???
I should have mentioned in my previous post that series arcing will not cause a fuse to blow. In the case of parallel arcing the current may not be high enough to cause a fuse to blow. The arcing can, will, create sparks though.
Safety caps do fail short, not enough though to create a fault condition a fuse or breaker can clear. RIFA caps in old Mark Levinson gear are notorious for this.
If it's the "round cylinder", it is possible that something conductive shorted the power supply cap or caused a voltage reversal. Who knows, a discarded component lead was dropped inside the unit during production and wiggled its way to a bad spot during shipping/setup.
Thanks for the responses. As far as I know the fuses are intact. I stopped the sparks shooting out the top by unplugging it. I took it to the NAD authorized repair facility and they said a faulty power supply caused the round cylinder ( not sure of part name) to explode which probably damaged the board and other parts. I can send pics if anyone wants to see the damage. Thanks.
@jea48, Jim, I took a look at the service manual for the M3, which can be seen at hifiengine.com if one is registered there. It appears that it has three fuses, all of which are AFTER an EMI filter, consisting of inductors and capacitors, which is connected between the incoming AC and the rest of the amp.
There are two 5 amp fuses (assuming this is a 120 volt model), one for each channel, with the main (rear panel) power switch connected between the filter and these fuses. There is also a 100 ma fuse protecting standby-related circuitry, with a relay connected between the filter and this fuse.
All of the fuses are located inside the unit, and they are not accessible on the rear panel.
All of this would seem to cast suspicion on the EMI filter as the culprit, although secondary damage elsewhere within the unit certainly may have occurred.
Odd the AC line safety fuse did not blow. The fuse should have blown protecting the unit from becoming a fire hazard. Is the AC Line fuse the original OEM fuse that came with the amp?
If it is the original OEM fuse I suggest you contact NAD service Tech support.
Or you could throw it from a great height onto a trampoline. Or hey I know, shoot it with a sniper rifle from a mile away! If you do this remember, one camera and mic on the rifle, another high speed on the NAD.
Or wait! Even better! Hook it up with some sparklers and stuff and recreate the event. First go down to Goodwill, pick up a rack and some stereo gear for like $5, make a video of the whole thing burning down. Not sparkling, burning down. Like you went out to check the mail and left the camera running. Then go down and shoot video of the local fire department. Put it all together so it looks like NAD burned your house down. Email a copy to NAD. Ask about their warranty, and oh by the way would you be interested in commenting before I post this on youtube?
Consider sending it to the Hydraulic Press guy channel on You Tube and ask for some $$ when he makes thousands from the subscribers; People send him all kinds of stuff; Very entertaining and it’s for science.
I’ve had some equipment over the years I would have loved to send him;
I can't believe that happened to you; Did you buy it new? How freaking scary!
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