NAD 3020A Amplifier Low Volume

[maikelson]

Hi, I've dug out a NAD 3020A Amp from my parents gathering dust corner and taken on the so far enjoyable learning process of attempting to diagnose and repair its issue(s).

It powers on, all inputs and outputs seem functional. But the volume - at maximum - is only a whisper. Left and Right sound balanced. And the 5 power lights (indicating 1-35W) don't illuminate - I presume this could simply be the globes or a deeper issue.

I replaced 4 main caps (2200uf 35v) because they had some visible corrosion/leaking on top. This resolved an idle hum which is reportedly common in this amp. The volume may now be marginally better but is still a whisper.

As a next step I removed and tested 4 main transistors (2N3055 and MJ2955). They seem to be open in the appropriate directions and showing ~300ohm resistance (30x10) as per pictured multimeter.


I see some brown glue around some caps which I've read may become corrosive. Otherwise all appear to be intact, albeit aged and potentially dried. I figured I'd seek advice and direction before tinkering with any of these.


To my eye the circuitry seems without abnormality. Except perhaps some orange/brown residue at some of the soldering points - see left hand side as pictured - these align with 4 fuses (intact).

Any assistance is much appreciated.

 

[davenn]

Hi there,
welcome to EP

I replaced 4 main caps (2200uf 35v) because they had some visible corrosion/leaking on top. This resolved an idle hum which is reportedly common in this amp. The volume may now be marginally better but is still a whisper.

That's not from the cap's but considering the apparent age of the unit, replacing them isnt a bad idea
In fact, I would be suspicious of all electrolytic cap's

I see some brown glue around some caps which I've read may become corrosive. Otherwise all appear to be intact, albeit aged and potentially dried. I figured I'd seek advice and direction before tinkering with any of these.

Taking out one of the glued caps and looking underneath it would con\firm if there has been any corrosion
probably not ( but maybe)
As said, replacing them all would be good, they have all probably dried out inside to some extent

Except perhaps some orange/brown residue at some of the soldering points - see left hand side as pictured -

That's just a bit of solder flux

cheers
Dave

 

[Bluejets]

That old meter may or may not be capable of providing enough bias to test transistors.
Usually when they have a x1 range but none on this antique.
Could verify by testing say an 1N4004 diode or similar.

What are you using as an input..?
What sort of voltage levels are you getting on the rectifier output and on the adjacent caps ..?
Rectifier is the rectangular part centre of where you removed the output transistors.photo #5
Caps for the dc output are the 4 adjacent I'd imagine.

 

[maikelson]

Thanks davenn, very helpful. I notice in the service manual parts list CER, MY, and ELEC Caps. Assuming these correlate to Ceramic, Mylar, and Electrolytic. Assuming age related deterioration would your recommendation be to replace only the Electrolytic Caps?

Bluejets, thanks for the illuminating comment regarding my old meter. I'm struggling to find good instructions on the tests you've mentioned. Could you please explain how I would do so?

 

[Bluejets]

Bluejets, thanks for the illuminating comment regarding my old meter. I'm struggling to find good instructions on the tests you've mentioned. Could you please explain how I would do so?

Not knocking your meter, I use a similar analogue meter myself sometimes.
The meter must be capable of providing enough bias to turn on the junction of a semiconductor.
It is why you will see modern digital meters with a "diode test" range as their ohm scale just will not work.
Normally, analogue meters such as you have there would have a 1 x range which would be ok for testing semi's.
When switched to the higher ranges they will not normally provide the bias drive.
It may well be your meter will do ok as there is no 1 x range which is why I suggested testing on a fairly standard diode such as an 1N4004.
This will also be a good test for future reference as well as sometimes, meters such as yours, have the positive and negative switched differently on ohm test.

 

[Martaine2005]

What’s that three legged component next to C637?. Just above the transformer in your last photo.
It looks rather malformed.
As previously said, ALL the electrolytics should be replaced as a matter of course.
During the 80s, many companies used glue for components which did indeed prove to turn conductive. This should also be carefully removed/scraped away. Then try the amp.
Use a good contact cleaner on all switches and pots too.

Martin

 

[maikelson]

What’s that three legged component next to C637?. Just above the transformer in your last photo.
It looks rather malformed.
As previously said, ALL the electrolytics should be replaced as a matter of course.
During the 80s, many companies used glue for components which did indeed prove to turn conductive. This should also be carefully removed/scraped away. Then try the amp.
Use a good contact cleaner on all switches and pots too.

Martin

It's a 2SD669. I think the light casting a shadow gives the illusion of it being malformed. Unless you mean the degree to which it leans?

Thanks for clarifying replacing the electrolytics. I'll do that and a clean as directed.

 

[Martaine2005]

Unless you mean the degree to which it leans?

No, not the leaning, it looks burnt/melted in the photo.
But obviously light plays tricks in photos.

Martin

 

[davenn]

Assuming age related deterioration would your recommendation be to replace only the Electrolytic Caps?

Yes
Ceramic and mylar will last a lifetime and more
Electro's are the most unreliable component on the planet

 

[Bluejets]

No voltage readings yet..??

 

[maikelson]

Just finished replacing all bar 4 elec caps, awaiting delivery of the these final few. Warmed it up to test and it's working and sounding glorious. I found some oxidation on the legs of some of the caps I removed so perhaps that and/or their age was the issue.

Thank you all for your help.

 

[Martaine2005]

found some oxidation on the legs of some of the caps I removed so perhaps that and/or their age was the issue.

The oxidation was probably due to age but electrolytic caps dry out over time and can become ‘resistors’ or ‘short circuits’ causing all sorts of problems.
Glad it’s working now. Don’t forget to clean all switches and potentiometers too.

Martin

 

[Technomaniac]

A lot of amps of this vintage have two pairs of RCA sockets with wire links joining them. The links can be removed if you want to insert an external graphic equaliser in the middle of the amp circuit. Sometimes when you acquire an amp the links are missing, which can confuse, as the amp doesn't work or has low gain. But also, if the links are present, they can be a source of poor performance, and should be polished up. They are sometimes chrome-plated and can oxidise.
The old 200H multimeter you have is same as the first I bought myself when I was still at primary school. Nothing wrong with them, but lacking a low ohms scale. When I started my apprenticeship, I bought an AVO 8 Mk.III to use at work. I still have both of them, 50 years later. Just check that your amp has an earth in the mains cord.

 

[Duni]

Just finished replacing all bar 4 elec caps, awaiting delivery of the these final few. Warmed it up to test and it's working and sounding glorious. I found some oxidation on the legs of some of the caps I removed so perhaps that and/or their age was the issue.

Thank you all for your help.

Hello,
I have the same model (nad 3020A) with exactly the same symptoms. I tried replacing all electrolitycs caps, but it did not solve the problem (it did made the volume a little better and removed the hum)
So I would like to know what exactly you changed that solved the problem please. I did not understand what were "bar 4 elec caps" but since I changed all elec caps... I suspect I should change C601, C602, C603 and C604 but I am not sure.
Visualy there is no problem on the board (there was the same brown glue). Everything else works, so it is a bit frustrating to see it work better and better but not as intended :/

 

[maikelson]

Hello,
I have the same model (nad 3020A) with exactly the same symptoms. I tried replacing all electrolitycs caps, but it did not solve the problem (it did made the volume a little better and removed the hum)
So I would like to know what exactly you changed that solved the problem please. I did not understand what were "bar 4 elec caps" but since I changed all elec caps... I suspect I should change C601, C602, C603 and C604 but I am not sure.
Visualy there is no problem on the board (there was the same brown glue). Everything else works, so it is a bit frustrating to see it work better and better but not as intended :/

Hi Duni, I'm a novice so can only provide suggestions based on my limited experience.

By "bar 4 elec caps" I meant I replaced all the caps except for those 4 listed. I would start by replacing those and see if it fixes your issues. I didn't have to replace every cap to solve my issues but decided to do so given the age - I figured a full refresher wouldn't hurt. Perhaps one or many of those final 4 are the cause of your issue. Failing that the fault could be in a or some resistors.

Coincidentally as of recently I've decided to open the amp again and do a maintenance check. I think Martaine2005's suggestion of cleaning switches and potentiometers is worth doing while you're in the process of repair. I'm noticing - after a year or so of use - some scratchiness and inconsistency with the volume knob. If your amp is like mine it needed a thorough clean of dust and there was some oxidation on some metal components. For reference I live in Qld, Australia - a hot and humid climate - which is not friendly to electronics.

Hopefully this helps. And given I'll open mine again soon perhaps I can be of more assistance once I'm familiar with it again.

 

[Technomaniac]

Hi, All. The said multimeter WILL check transistors OK. But one thing that has not really been brought up here, is the brown glue. It was used to secure some components to the PC board. Unfortunately it becomes conductive with age, You can measure its resistance with an ohmmeter on the high range. Originally it was yellow contact cement and a reasonable insulator. But when it turns brown it becomes a conductor. You have to use one of those blue-handled tools that has an end like a wood chisel, about 5mm wide. It will be a painful job. After it has been chiseled away, the board will need to be flushed with methylated spirits and allowed to dry thoroughly. If the metho makes the board look cloudy, a thin film of RP7 or Inox or any light oil can be brushed on with an artists brush. Not too much, as dust will stick to it and cause trouble later when it rains.
IF this amplifier has any rotary switches, have a good look at the shaft where it goes through the wafer(s). Some wafer switches had shafts with cadmium plating. Over time, the cadmium grows "whiskers" which are conductive, and can short circuit between the shaft (which is ground) and the moving contacts on the little fibre disc. These cadmium whiskers have a very low resistance. I can't remember whether the Japanese wafer switches used cadmium, but it was certainly a regular problem on waveband switches in AM radio chasses. Another thing you can check, cobwebs sometimes become conductive. I don't know why, but I had a secretary once who had her TV into the firm for whom she had previously worked, they were unsuccessful in the repair. She brought it to work one day and because I am in the habit of using binocular magnifiers, I saw the cobweb within minutes. Another thing, if a resistor close to the PC board has incinerated at any time, there could be burned PC board, which is also conductive.

 

[Technomaniac]

Maikelson, I too am in Queensland. Regarding scratchy potts, If cleaning is not enough to remove the scratchiness, I was told this by a technician working for an associated firm which had a large inventory of Jukeboxes. His remedy was removing the back of the potentiometer and physically relocating the wiper by careful bending, so that it traversed a brand new path along the carbon. I have since used this method successfully, many times.

 

[Martaine2005]

During the 80s, many companies used glue for components which did indeed prove to turn conductive. This should also be carefully removed/scraped away. Then try the amp.
Use a good contact cleaner on all switches and pots too.

But one thing that has not really been brought up here, is the brown glue. It was used to secure some components to the PC board. Unfortunately it becomes conductive with age,

Martin

 

[Duni]

Thank you all for your answers!

I also am a total novice, that's why I hoped for a simple fix
I am not sure about the 4 1uF 25V caps because the low volume is the same on both channels, and they seem good... I'll try to replace them as soon as I get my hands on replacement parts.

I've cleaned a lot of dust out of it, every resitor /fuse I tested was good, I'll check again to be sure.
I've also cleaned switches and potentiometers, I've not taken them apart, because at max volume I can hear music, so I know that every one of them works (bass control, treble, volume and balance works).

I've not found any oxydation while removing all the caps, but the amp stopped working after being stored for a long time so I figured the caps did not like that.

Regarding the brown glue, most of it was ON the caps, so I removed it by removing the caps. the rest of it was not located on any traces or components. I removed everything I could and tested again but it did not fix the issue.

I did not find any cobwebs, I've checked again for blown components, I'll upload some photos later if you see something I don't...

 

[Martaine2005]

Problem is… most people don’t know about dried capacitors and turn the item on. Those dried capacitors can simply cause noise or more dramatically blow the unit up.
you said remove. Did you replace?

Martin