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Old 12th January 2013, 06:06 PM   #1
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Default Have I wrecked my amp

Hi,

I have a NAD 3240PE amp. I have owned this amp for a bout 20 years and today while moving things about managed to let the banana plugs form one speaker cable touch, I can't believe I was so careless but there you go. There was a flash from the amp and a burning smell and now that one channel is dead. Is there any hope ?

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Old 12th January 2013, 06:14 PM   #2
Mooly is online now Mooly  United Kingdom
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There's always hope... but it depends on your skills and ability.

Impossible to say exactly what you have done but chances are the output stage has gone pop. That will be the main output transistors, probably also driver transistors too and collateral damage such as any low value resistors around that area.

One things for sure... you need the top off and to do few very basic checks to see the state of play.
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Old 12th January 2013, 07:31 PM   #3
jaycee is offline jaycee  United Kingdom
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Not wrecked, but will require repair... as Mooly says, you will at least need the output transistors replacing.
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Old 12th January 2013, 11:06 PM   #4
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With much skill (and new parts) you may be able to put the smoke back into your NAD.
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Old 12th January 2013, 11:14 PM   #5
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Does this usually happen when two wires touch? As I have done it a few times with my old luxman l-200 and nothing bad has happened. Not even a fuse blew.
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Old 12th January 2013, 11:15 PM   #6
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The first stop is output transistors, check them for shorts S-D or C-E.

If they are blown replace them then power up with mains lamp in series.
If the lamp doesn't stay lit then the amp is probably fine.
If it stays lit then there are further problems.
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Old 12th January 2013, 11:38 PM   #7
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Quote:
Originally Posted by Mooly View Post
There's always hope... but it depends on your skills and ability.

Impossible to say exactly what you have done but chances are the output stage has gone pop. That will be the main output transistors, probably also driver transistors too and collateral damage such as any low value resistors around that area.

One things for sure... you need the top off and to do few very basic checks to see the state of play.
Thanks for all the quick replies.

So it is looking bad then. I have no skills or abilities and would require someone else to help me out here. I can only visually check if that is any use. Where can I get help, how much is it going to cost me and is it going to be worth it.
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Old 13th January 2013, 02:00 AM   #8
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Quote:
Originally Posted by Kermit100 View Post
I have done it a few times with my old luxman l-200 and nothing bad has happened. Not even a fuse blew.
Not all amplifier designs behave the same way with a dead short placed across the output. For various reasons, some brands use no relay or similar switched protection at all. Obviously, they are vulnerable to careless handling and speaker faults but then, new buyers are often very careful to preserve their warranty; adhering to the installation instructions, so the problem doesn't arise there.

As a matter of interest, early NAD amplifiers like 3020 and 3240 series, all used thermal-magnetic switches on the output rail. These respond very slowly and afford little useful protection to shorts. When extremely cost-cut designs are out there, these are the problems we get.

Luxman L200 is also bottom-of- the-line but being Luxman, with a reputation to maintain, it uses cheap, instant, electronic VI limiting circuitry (Q106,7) which, though criticised for audiophile reasons is quite effective in most situations. Even Naim use it.

Bolier, depending where you are located, a service agent for NAD or any electronic service agency capable of proper audio repairs can do the work for you. Of course, nothing is free but if you don't value your amplifier particularly, there will be others who do. Sell it as blown in one channel, if you need to.
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Old 13th January 2013, 03:00 AM   #9
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For those who haven't seen a thermal magnetic switch or more correctly, a self-resetting thermal protection switch as used by NAD, this should help. It can be that the contacts in these are are badly burnt in a short also and need replacement - not always easy as there are now few suppliers. http://www.altronics.com.au/index.as...=item&id=S5623
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Last edited by Ian Finch; 13th January 2013 at 03:03 AM.
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Old 13th January 2013, 03:07 AM   #10
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Schematic Attached that may help to explain condition of short on output transistors, and assist replacement by Nad repair shop.
Attached Files
File Type: pdf NAD 3240PE.pdf (551.9 KB, 60 views)
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