NAD 2400 problem - need help

dan4 · 10th March 2005, 06:48 AM

I am looking to obtain a schematic and possibly some direction as to fix my NAD 2400 amp.

Here's what happened. I loaned my pre-amp and amp to a friend that was wiring his house for in-wall speakers. We had three sets of speakers (8ohm) hooked up in parallel. We were using impedance mathing volume controls (at x4 resistance setting). My friend disconnected one set of speakers (After the volume control) but did not disconnect the wiring to the volume control. He turned on the system to listen to music on the remaining sets. Music played for about two minutes and then the amp blew the main fuse (5mF 125V 7A). After consulting with an electrical engineer at work, he told me that it was a bad thing to leave the one volume control hooked up (the one without speakers attached). The volume controls were Phoenix Gold VMT100

I replaced the main fuse, plugged it in, and nearly instantly blew the fuse. I tried again and blew the second fuse. Obviously I have a problem.

Does anyone have a hypothesis as what is wrong or what is the next diagnosis step? I am thinking it is the transformer. Can someone provide me with a schematic for a 2400?

NUTTTR · 10th March 2005, 11:56 AM

From memory, if you find the fuse is blowing straight away you will most likely find the outputs potentially are blown... Not sure on the volume control causing the problem unless it was presenting a below 4 ohm load (from memory that nad's rated to 4 ohm min? or was it 2?)... Could have caused the amp to heat up a lot and blow the outputs... Of course, make sure everythings unplugged and measure the resistance on the connections of the output transistors (relative to eachother) if any of them are REALLY low like 1ohm, something like that, they are short, blown... Potentially it's more than just the outputs too, check diodes, resistors and small transistors within that circuit, sorry but i do not have a schematic for it
Good luck
Aaron

steven344 · 8th May 2006, 12:40 PM

I have a schematic if you need it

steven344 · 8th May 2006, 12:45 PM

schematic

steven344 · 8th May 2006, 12:47 PM

part 2

computeruser · 8th May 2006, 01:28 PM

The full NAD 2400 Service Manual has just been posted on
www.sharefx.com

10th March 2005, 06:48 AM	#1
dan4 diyAudio Member Join Date: Mar 2005 Location: WI	NAD 2400 problem - need help I am looking to obtain a schematic and possibly some direction as to fix my NAD 2400 amp. Here's what happened. I loaned my pre-amp and amp to a friend that was wiring his house for in-wall speakers. We had three sets of speakers (8ohm) hooked up in parallel. We were using impedance mathing volume controls (at x4 resistance setting). My friend disconnected one set of speakers (After the volume control) but did not disconnect the wiring to the volume control. He turned on the system to listen to music on the remaining sets. Music played for about two minutes and then the amp blew the main fuse (5mF 125V 7A). After consulting with an electrical engineer at work, he told me that it was a bad thing to leave the one volume control hooked up (the one without speakers attached). The volume controls were Phoenix Gold VMT100 I replaced the main fuse, plugged it in, and nearly instantly blew the fuse. I tried again and blew the second fuse. Obviously I have a problem. Does anyone have a hypothesis as what is wrong or what is the next diagnosis step? I am thinking it is the transformer. Can someone provide me with a schematic for a 2400?

8th May 2006, 12:40 PM	#3
steven344 diyAudio Member Join Date: Jun 2005 Location: ohio	nad 2400 I have a schematic if you need it

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10th March 2005, 11:56 AM	#2
NUTTTR diyAudio Member Join Date: Nov 2004 Location: Australia!	From memory, if you find the fuse is blowing straight away you will most likely find the outputs potentially are blown... Not sure on the volume control causing the problem unless it was presenting a below 4 ohm load (from memory that nad's rated to 4 ohm min? or was it 2?)... Could have caused the amp to heat up a lot and blow the outputs... Of course, make sure everythings unplugged and measure the resistance on the connections of the output transistors (relative to eachother) if any of them are REALLY low like 1ohm, something like that, they are short, blown... Potentially it's more than just the outputs too, check diodes, resistors and small transistors within that circuit, sorry but i do not have a schematic for it Good luck Aaron

8th May 2006, 01:28 PM	#6
computeruser diyAudio Member Join Date: Dec 2004 Location: Montreal	The full NAD 2400 Service Manual has just been posted on www.sharefx.com

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