NAD 3020A Preamp Woes

[paickda]

Hi forumers,

I hate to start another NAD thread but most contain dead-ends or are not tailored to my needs - trust me, I've been through about 15+.

I just obtained a second-hand NAD 3020A from eBay off a man who had the amp in storage for many a year. I got it in a nice state, clearly dusty but I took care of that promptly and also applied some contact spray, all over.

However, with the NORMAL IN and PREAMP bits bridged and with something in AUX/TUNER/etc, there is only a very, very faint sound being outputted. Changing the volume knob does not alter the volume of the faint sound. Plugging in headphones doesn't make a difference - in the cans there is still that faint sound output.

However, plugging the source straight into NORMAL IN (thus, bypassing the preamp section) yields a beautiful result - clean and pure sound. So I'm guessing there is nothing wrong with the power amp side of things but more so to do with the preamp.

Now, I'm no wizard with electronics but if anyone is able to kindly push me in the right direction of what I should do next, that would be greatly appreciated. I still haven't been able to find a service manual that is of the NAD 3020A variety (that pdf that is hosted on the mac host is dead and others that I have come across have dead links).

I've also attached some images to try and assist the process:
NAD 3020A - Imgur


Any help appreciated!

[Mooly]

Check for physical damage such as cracked print around any of the rotary controls before delving too deep. Running short of time... manual available here ?

NAD 3020 | Owners Manual, Service Manual, Schematics, Free Download | HiFi Engine

[powerflux]

did you try vigorously pressing/depressing the 'tape' button? :P

[planet10]

Originally Posted by Mooly

HiFi Engine

Neither of the service manuals they link are for 3020A. Here it is:

http://p10hifi.net/planet10/manuals/...viceManual.pdf [11MB]

dave

[jaycee]

see where the signal goes bad. a scope is best for this but you can get by using a pair of 32 ohm headphones to pick up the signal. I'd test on the end of R501/502, the wiper of VR1 (the volume control), and the negative end of C517/518.

possible candidates for problems are the small signal coupling electrolytic capacitors, bad switches, or the transistors in the preamp stage Q501-Q506. The 2SC1400 might be difficult to replace - recommended replacement is 2sc2632 however this is end of life also. Fairchild's KSC2316 seems ideal.

[paickda]

Originally Posted by planet10

Neither of the service manuals they link are for 3020A. Here it is:

http://p10hifi.net/planet10/manuals/...viceManual.pdf [11MB]

dave

Thanks for this service manual. There is still a slight difference compared to my board though (for example, the 4 caps are in a different position).

It will hopefully suffice, so thanks again.

Originally Posted by jaycee

see where the signal goes bad. a scope is best for this but you can get by using a pair of 32 ohm headphones to pick up the signal. I'd test on the end of R501/502, the wiper of VR1 (the volume control), and the negative end of C517/518.

possible candidates for problems are the small signal coupling electrolytic capacitors, bad switches, or the transistors in the preamp stage Q501-Q506. The 2SC1400 might be difficult to replace - recommended replacement is 2sc2632 however this is end of life also. Fairchild's KSC2316 seems ideal.

Thanks for starting me off. Will attempt this weekend!

[availlyrics]

I have NAD C352 amp & had somewhat similar problem- Left ch. very faint sound- & Right ch. proper sound, when I directly connect CD player to power amp sec. proper sound but no control over vol./balance/tone.
Soln. bal. pot (20K lin) gone bad in pre-amp sec. , I replaced it with 10K+10K resistors for both L & R CH. (didn't needed those bal. controls anyways) & also dry soldered all transistors points.

[paickda]

UPDATE: NAD repaired successfully. In the end, it all just came down to a faulty electrolytic capacity C513 (47u10V) in one side of the preamp stage. Originally I thought it was transistor Q501 (BC559B). Phew! Now I may as well re-cap the others! Cheers forumers.

[Mooly]

Thanks for the update. Pleased to hear you have fixed it.