Author Topic: DIY for NAD 7020 Amplifier  (Read 527 times)

Offline phasor

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DIY for NAD 7020 Amplifier
« on: February 15, 2017, 09:32:50 PM »
I hope I'm posting this in the correct section. Mods, if I'm wrong please can you assist by moving this.

I have a NAD 7020 which I bought for my Dad a few months ago. It was working okay but with scratchy sounds when raising or lowering the volume. I used some contact cleaner on the pots and now it seems to make a popping noise from the amp even if the volume is completely off. It does this on any source even a source which is not connected.

The only way to stop it is to select another set of speakers, eg Speaker B or OFF.

Any thoughts on what could be wrong?

Offline peterc

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Re: DIY for NAD 7020 Amplifier
« Reply #1 on: February 20, 2017, 12:54:53 PM »
HI Phasor

How old is the amp?
Could be that it needs a recap job,electrolytic caps start drying out after 10-15 years.

Could also be a component slowly dying.

Could also be a ground connection that is loose, or a cold solder joint.

Good luck!
Peter

Offline Ampdog

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Re: DIY for NAD 7020 Amplifier
« Reply #2 on: February 20, 2017, 03:24:07 PM »
The post is puzzling.

Scratchy noise when a volume control is adjusted can come from the volume control only. But the influence of another loudspeaker of all things complicates matters - if I understand correctly. This leans me to believe that somehow there is a dc voltage over the volume control (most pots will cause a scratchy sound if rotated with dc across it). The presence or not of such dc needs to be investigated. Primary culprit a leaky coupling capacitor, after that - a whole lot of other probable causes. One cannot enter into those without examining the amplifier
Creativity requires the courage to let go of certainties.  (Erich Fromm)

Offline phasor

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Re: DIY for NAD 7020 Amplifier
« Reply #3 on: February 20, 2017, 04:15:49 PM »
Thank you both for the response. Really great that I'm using the forum for some good that might benefit others instead of spending money on it all the time 😁

I would have thought the caps also but I thought maybe the fact that I sprayed the pot just before this happened had something to do with it.

The other thing that I noticed upon inspection was a small straight pin (like tailors use) which I found lying on the board. Perhaps the previous owner or his kids had dropped one in by mistake. I'm wondering what damage this short might have done.

By the way the second set of speakers is a red herring in my opinion. Since there were no speakers connected to those terminals that switch was doing exactly what it's supposed to do and isolating the speakers when in the Off position.

Do we have a NAD guru who could look at this for me?


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Offline Qualityten

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Re: DIY for NAD 7020 Amplifier
« Reply #4 on: February 22, 2017, 12:28:36 AM »
I worked on a faulty NAD 7020 with the help of members of the UK vintage radio restoration forum in Dec-Jan.  The thread is here: http://www.vintage-radio.net/forum/showthread.php?t=132080

If you are handy with a soldering iron and can check your work with a circuit diagram, you should be able to replace all the capacitors for not too much money, though quite a bit of time.  I only found one faulty capacitor, but the results are still very worthwhile.   The suggestions made already are all valid, as the quality of assembly of these units was not very high and a dry solder joint is possible. I reflowed all the joints when I recapped mine.

If you want to pursue a remote fault check, you would need to describe the problem accurately as possible.  I admit that's not easy.  As to your question about the pin, it would depend where the pin was lying on the circuit board.

Offline peterc

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Re: DIY for NAD 7020 Amplifier
« Reply #5 on: February 24, 2017, 12:07:11 PM »
Phasor

Another thing to try is spraying out the switches as well, if they are not sealed. They can also be noisy.

Where are you situated?

Peter

Offline phasor

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Re: DIY for NAD 7020 Amplifier
« Reply #6 on: February 24, 2017, 12:09:59 PM »
Hi Peter
I have sprayed the selector switches and a great deal of the drop outs were caused by those. But this is most likely not caused by this because it doesn't get affected when rocking the switches.
I'm in Forest Town Jhb.


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Offline Ampdog

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Re: DIY for NAD 7020 Amplifier
« Reply #7 on: March 05, 2017, 06:02:05 AM »
I am not so sceptical regarding capacitors. Capacitors (including electrolytics) of the 90's were already pretty modern, and did not go faulty/dry-out nearly as often as from say the 50s. Still that does not exclude weak/faulty ones, but then from poor quality, not mere age.

But if one does not have a testing device - a multimeter can also serve - the low expense might be considered worthwhile. I am simply stating that this idea of "replacing caps" per se seems to have become a fixation rather than supported by facts. {How often have those servicing amplifiers come across a confirmed bad modern capacitor in their careers? Never, from this person. E.g. electrolytic caps in my s.s. amplifier built about 1997 are still on par despite the unit being on permanently excluding power cuts. (They are Hitanos)]

Caveat: Capacitors salvaged from PCs. They are some of the best examples of built-in obsolescence to be found these days.               
Creativity requires the courage to let go of certainties.  (Erich Fromm)

Offline Qualityten

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Re: DIY for NAD 7020 Amplifier
« Reply #8 on: March 13, 2017, 11:57:47 PM »
The NAD 7020 dates from the late 70s/early 80s, so is 30-40 years old now.

However, the problem does sound more switch cleaner related.  What did you use?  I prefer Servisol.

Offline kubusi

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Re: DIY for NAD 7020 Amplifier
« Reply #9 on: March 16, 2017, 06:53:04 PM »
Ampdog, noticed your comment about salvaged capacitors from PC's, I wonder if you could give a bit more information to enlighten us, I have used capacitors in a number of projects for years with no apparent problems so far, possibly I have been lucky. What I have aways done after removing items is check them on a bridge for value and then at operating voltage for leakage, I have found dicky ones and I had always put it down to too much heat involved when removing them. Possibly they were already faulty before removal, I had not thought of that before. Thanks for the warning I must keep it in mind.
I also salvage items from faulty energy saver lamps,  diodes, low value resistors and capacitors,  both the  low value 400 volt electrolytics and  others.
The need for excercise is a modern superstition, invented by people who ate too much, and had nothing to think about. Athletics don't make anybody either long-lived or useful.

George Santayana