NAD3140 problem

[JPhilips]

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]

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]

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]

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]

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]

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]

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]

...... i hope it's a success.

Excellent. Many thanks.

Andy

 

[JPhilips]

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