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Old 14th February 2007, 04:13 PM   #1
boas is offline boas  Denmark
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Default My amp only works after a while, or when turned up loud.

After a long search I found this great site.
I'm a poor student, trying to find a way to repair my beloved old hifi amp, and I thought maybe someone in this forum could help me out...

I have an old NAD 2200 power amp, and a NAD 1155 preamp. The problem is that the amp only plays in the right channel when just powered up. If I turn op loud the left channel works after some "scratching". When I turn the volume down again, it usually stops working in the left channel again.
The problem is related to the power amp, because it disappears if I change the power amp.
If I leave it on for several hours it works fine and plays great, but due to electricity useage that it not a convenient sollution.
So anyone has a comment on this? Any help would be much appreciated!!
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Old 14th February 2007, 04:32 PM   #2
Netlist is offline Netlist  Belgium
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Apart from the normal procedure to blank resolder the PCB and hunt for bad capacitors, check C401/402/403 and 404, resolder RL401 and RL402 and suspect the output relays.

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Old 14th February 2007, 06:56 PM   #3
Minion is offline Minion  Canada
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You might also check the Volume Pots to see if they are still good....It could be that there are ares of the Pots carbon resistor disk that could be worn away and this is why it only works when cranked up loud and why it is "Scratchy"......

Just a Thought.....
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Old 14th February 2007, 07:34 PM   #4
Tim__x is offline Tim__x  Canada
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Sounds like a problem with the speaker muting relay.

I see Netlist already suggested this, so I second his response.
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Old 14th February 2007, 10:01 PM   #5
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Agree with Minion bad or dirty volume control.
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Old 14th February 2007, 10:15 PM   #6
Ron E is offline Ron E  United States
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I concur with most of the others here.

Scratching is most likely a potentiometer problem. Sometimes you can fix this temporarily by turning it all the way up and all the way down (amp turned off) a few times. If 5-10 times doesn't work you must clean it or replace it.

The "turn it up and it plays" problem is likely a speaker protection relay (usually a little black or blue box near the heatsinks).
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Old 14th February 2007, 11:02 PM   #7
djk is offline djk
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The NAD 2200 had a history of bad relays, even when they were new.
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Old 15th February 2007, 01:01 AM   #8
Leolabs is offline Leolabs  Malaysia
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Actually you try to open the VR and look for bad(bend) viper.
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Old 15th February 2007, 03:37 AM   #9
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i don't recommend the inexperienced to open up pots, at least until they have practiced with a few from a junk parts box.
potentiometers have mechanisms that vary from manufacturer to manufacturer, and some manufacturers use different types of construction in their product lines. potentiometer rebuilding is an accquired skill. some pots use front pressure, some rear pressure, some use both, some use spring arms, some use wavy washers, etc....
it's good to get some practice before attempting to rebuild a pot in a working piece of equipment.
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Old 15th February 2007, 06:50 AM   #10
boas is offline boas  Denmark
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Thank you for all the replies!! I really appreciate it.
I don't think it has anything to do with the vol-potmeter though, because the problem is with the poweramp which doesn't have a volume control.

I will try to measure the other mentioned things here.
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