NAD 3020A died last night...

[D3vil99]

Hey guys, I can't believe I remembered my username and password.

So my trusty 3020A died last night while listening. Right channel went low to silent, followed by the left. No audio. Turned it off and back on and now it only hums on power on. I don't know what it could possibly be, I don't suspect the pre-amp died or the output stage cause when I press my fingers on the preamp/amp terminal lugs on the back it hums a bit more. Opened it up, I don't see any blown resistors, capacitors or fuses.

Any advice or assistance would be grateful.

 

[leesonic]

If it's never been restored, it's still running on 40 year old caps. Unless there is a catastrophic failure, you won't see a blown cap.

You can always pull the pre/power amp jumpers, and see where the problem is, with the preamp or the power amp. You can feed a signal from the preamp into something else, and feed a signal from something else into the power amp.

The best place to start looking is measuring the power supply voltages, and see if they match what is on the schematic. The four big caps in the middle should have approx +-30V across them. The last caps in the power supply C913 and C914 should have approx +30V and -25V on them.

 

[tadawson]

Both channels at about the same time tends to rule out issues in the power amp and premp proper, as does it's ability to output hum. This sounds like a low voltage supply feeding the pre has folded, and is consistent with old caps as stated above. One may have shorted and pulled a supply down.

 

[Gigantic]

I had one back in 1988 that died. My memory is not really great, but I recall they had some sort of transformer/relay problems on the input stage; I'm surprised yours lasted this long. As @leesonic mentioned, it's likely overdue for a capacitor refresh as well. I was an 18 year old college freshmen when mine went down and I couldn't afford to repair it, something I regret to this day. It's worth repairing, as it's a legendary integrated amp.

 

[WSideWitness]

Find a local tech to take a look. The 3020's are pretty easy to work on so hopefully it will be affordable for you. A properly rebuilt 3020(a) sounds incredible. Easily my favorite low power integrated amp from a strictly SQ standpoint.

 

[Don927]

Hey, just wanted to say the 3020 is legendary as you know. I bought mine new way back in the day (yes I'm old) and replaced it with a NAD 3155 which is an absolute beauty, new also back in the mid 80's. I've purchased and auditioned numerous amps over the years and have never found anything that outperforms my 3155. Anyway, the 3020 is terrific and worth repairing which I hope you've been able to do.

 

[D3vil99]

Thanks for the replies everyone. I disassembled it a bit more today and noticed where @leesonic said C913 & C914 sits on the back of the board is a little bit of dis-colorization from excessive heat. Behind those caps is another pair of caps sitting right next to a pair of resistors and transistors, those definitely have to be dried out. I don't have parts and would have to order so I'll probably update this later on.

 

[leesonic]

Post some pictures of the inside so we can see what version you have.

Your profile says you're in South Africa. What is it like sourcing capacitors there? Parts are getting scarce everywhere, I ran a BOM through Mouser electronics, and only two of the caps were actually in stock, all the rest were NLA. Granted, this was a BOM from a few years ago.

 

[D3vil99]

Here we go.

Tested all the electrolytics on the main and the section mentioned, all seem to hold charge with exception of one measuring 38uF instead of the spec 47uF. Tested transistors today in-circuit on the first half of the pre-amp stage. Also checked two JFETs on the balance section. All seems ok. Will check them out of circuit later and compare HFE.

Another person off forum suggested I take a look at the 3020B's Service Manual since the A share the same design with minor changes, already got that downloaded.

Getting parts might be a problem but we do have suppliers like Mantech, RS Components, Yebo Electronics and Communica.

 

[leesonic]

Still no mention of the power supply voltages that I suggested testing back in post #2. Did you measure these and see what the values were?