NAD3140 problem

JPhilips · 2nd December 2006, 04:12 AM

Does anyone have a schematic for the NAD3140. After replacing many overheated electrolytics just behind the volume control the amp works but the new capacitors still get hot!
Not too sure what this part of the circuit does but it appears to be a secondary power supply fed from one of the transformers through a small bridge rectifier.
The only clue soundwise is that line-level inputs (Aux, tuner etc.) produce quite a loud (50Hz) hum when connected to an external source but I notice that fed straight into the 'Lab-in' power amp input produces no hum. Surprisingly the phono input also produces no hum.
I'd really like to get it sorted as CD fed straight to the power amp section sounds - magic! so any help would be greatly appreciated.

cliffforrest · 2nd December 2006, 09:24 AM

Hot caps means they are either overvoltaged or passing too much AC.

The 50Hz hum suggests the latter.

Prime suspect is the bridge rectifier with one diode short-circuit.

Easy to meter it.

es44 · 2nd December 2006, 10:52 AM

Will a schematic of the 2140 be of any use ?
The 2140 and 3140 shares the power section, but of course there's no preamp in 2140.

Best regards
Ebbe

JPhilips · 2nd December 2006, 06:00 PM

Yes Ebbe I would appreciate a schematic of the 2140 as the small bridge rectifier is Ok and I notice some work has been done on the main rectifier/reservoir block which I assume is the same in both models.
I think the secondary power supply in the vicinity of the hot capacitors maybe a red herring as NAD made extensive use of jumper leads and the problem capacitors may receive voltage from the main power supply.
Just as you say Cliff, the DC voltage is either too high (which it isn't, as the measured DC is below the working voltage of the caps ) or there is too much AC which I think can only mean a bad P/S.
Thanks for your replies.

John

es44 · 2nd December 2006, 08:16 PM

Ok, let me have your email address, and i will send it. It's only a schematic though, but hopefully you can have some use of it.
It's 200Mb, so not that big either.

Best regards
Ebbe

poynton · 2nd December 2006, 09:02 PM

Quote:

Originally posted by es44
It's only a schematic though, but hopefully you can have some use of it.

Please post it using a hosting service.

eg.

http://www2.bigupload.com/upload2.php?r=1

I and others would like the schematic.

Thanks

Andy

es44 · 2nd December 2006, 10:26 PM

Done.
You should all be able to get it here: Nad_2140.Pdf.Zip by Bigupload.Com]Nad 2140 Schem
I never tried Bigupload before, so i hope it's a success.

Good luck
Ebbe

poynton · 3rd December 2006, 09:39 AM

Quote:

Originally posted by es44
...... i hope it's a success.

Excellent. Many thanks.

Andy

JPhilips · 3rd December 2006, 01:30 PM

Yes, many thanks Ebbe.
The problem area would appear to be in the top right hand corner of the schematic where almost all the electolytics have been replaced.

John

2nd December 2006, 04:12 AM	#1
JPhilips diyAudio Member Join Date: Jun 2006	NAD3140 problem Does anyone have a schematic for the NAD3140. After replacing many overheated electrolytics just behind the volume control the amp works but the new capacitors still get hot! Not too sure what this part of the circuit does but it appears to be a secondary power supply fed from one of the transformers through a small bridge rectifier. The only clue soundwise is that line-level inputs (Aux, tuner etc.) produce quite a loud (50Hz) hum when connected to an external source but I notice that fed straight into the 'Lab-in' power amp input produces no hum. Surprisingly the phono input also produces no hum. I'd really like to get it sorted as CD fed straight to the power amp section sounds - magic! so any help would be greatly appreciated.

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2nd December 2006, 09:24 AM	#2
cliffforrest diyAudio Member Join Date: Sep 2004 Location: UK	Hot caps means they are either overvoltaged or passing too much AC. The 50Hz hum suggests the latter. Prime suspect is the bridge rectifier with one diode short-circuit. Easy to meter it.

2nd December 2006, 10:52 AM	#3
es44 diyAudio Member Join Date: Apr 2005 Location: Fredericia, DK	Will a schematic of the 2140 be of any use ? The 2140 and 3140 shares the power section, but of course there's no preamp in 2140. Best regards Ebbe

2nd December 2006, 06:00 PM	#4
JPhilips diyAudio Member Join Date: Jun 2006	Yes Ebbe I would appreciate a schematic of the 2140 as the small bridge rectifier is Ok and I notice some work has been done on the main rectifier/reservoir block which I assume is the same in both models. I think the secondary power supply in the vicinity of the hot capacitors maybe a red herring as NAD made extensive use of jumper leads and the problem capacitors may receive voltage from the main power supply. Just as you say Cliff, the DC voltage is either too high (which it isn't, as the measured DC is below the working voltage of the caps ) or there is too much AC which I think can only mean a bad P/S. Thanks for your replies. John

2nd December 2006, 08:16 PM	#5
es44 diyAudio Member Join Date: Apr 2005 Location: Fredericia, DK	Ok, let me have your email address, and i will send it. It's only a schematic though, but hopefully you can have some use of it. It's 200Mb, so not that big either. Best regards Ebbe

2nd December 2006, 10:26 PM	#7
es44 diyAudio Member Join Date: Apr 2005 Location: Fredericia, DK	Done. You should all be able to get it here: Nad_2140.Pdf.Zip by Bigupload.Com]Nad 2140 Schem I never tried Bigupload before, so i hope it's a success. Good luck Ebbe

3rd December 2006, 01:30 PM	#9
JPhilips diyAudio Member Join Date: Jun 2006	Yes, many thanks Ebbe. The problem area would appear to be in the top right hand corner of the schematic where almost all the electolytics have been replaced. John

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