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.
Beware of NAD M3 Fire Hazard
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?
- ...
- 86 posts total
| Post removed |
heaudio123 Said: 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? heaudio123 Response: heaudio123100 posts 03-15-2020 3:19am 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? heaudio123 Said:heaudio123,Could be anything, but a shorted diode in the bridge passing AC and cooking the capacitor would be my guess. 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? Jim . |
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 |
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. |
- 86 posts total