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Nad 3020A developed problems
Nad 3020A developed problems
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Old 8th June 2021, 06:58 PM   #1
Peterbt is offline Peterbt  France
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Default Nad 3020A developed problems

Hi

Newbie here so go please go slow
My NAD 3020A has developed a fault. When I turn it on it's okay for about two minutes. Then the sound begins to fade, turns gritty and cuts out almost totally. When I turn it off then back on again it will do the same. I have a couple of Nakamichi decks, a CD player and a turntable hooked up to it. It's the same on all. Nu hum or any other unwanted noises. I am not a pro but have some limited electronic knowledge, a DMM and some soldering capabilities. I wonder if it's something I can fix or considering its age it's bust or it needs a pro. It has been working perfectly over ten years. I appreciate any help. thanks.
peterbt
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Old 8th June 2021, 07:04 PM   #2
Mooly is offline Mooly  United Kingdom
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Nad 3020A developed problems
Welcome to diyAudio Peter

If both channels are doing the same then this could be something really simple like a loose fuseholder or an intermittent mains switch.

For both channels to fade it would suggest a possible supply problem.

Also it might be the 3020 that uses a FET muting arrangement between pre and power amp sections and that could give these symptoms. You would need to do some very basic voltage measurements.

From memory if it does have that arrangement then it could also again be mains switch related (auxiliary contact on switch).

There is another thread on that somewhere and I remember simulating the mute circuit for someone.
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Old 8th June 2021, 07:07 PM   #3
Mooly is offline Mooly  United Kingdom
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Nad 3020A developed problems
It was this thread I think (NAD 3020 may be very similar).

DC offset on NAD 3120 preamp output
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Old 8th June 2021, 07:13 PM   #4
Peterbt is offline Peterbt  France
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Default NAD 3020

Thanks for that.
I'll take it down, disconnect everything and check out the fuses and the mains switch but I don't understand why the sound gets so gritty before it cuts out and also why it functions just like normal for about two minutes
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Old 8th June 2021, 07:23 PM   #5
Mooly is offline Mooly  United Kingdom
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Nad 3020A developed problems
The gritty sound could well be a symptom of the FET muting (we are assuming at this point it does have that) and occurs as the FET slowly becomes non linear as the gate voltage drifts ever lower (more negative). It would be a classic symptom.

You will need the correct circuit diagram to refer to but that other thread should give you a good start. If it is around that area then small caps related to the generation of the FET gate voltage could be at fault

I'll look in again tomorrow (out of time today)
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Old 8th June 2021, 07:27 PM   #6
Mooly is offline Mooly  United Kingdom
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Nad 3020A developed problems
Here is a NAD circuit. The switch (I think is a 3rd contact on the mains switch) could be the culprit.

You need to check the voltage at the point arrowed when the fault occurs, If this is negative then the FET's are cut off and the unit is in mute. If the voltage drifts across that threshold the sound will become very distorted as the FET is neither on nor fully off.
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Old 8th June 2021, 08:14 PM   #7
Goldie99 is offline Goldie99  United Kingdom
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If it's both channels, try checking C531 in the muting circuit - that's a good candidate that often fails.



Alan
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Old 8th June 2021, 08:46 PM   #8
Peterbt is offline Peterbt  France
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Thanks, is that a large or a smaller cap? And what value? I have a number of them in stock. Most of them for the power supply of my Nak tape decks.
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Old 8th June 2021, 10:43 PM   #9
indianajo is offline indianajo  United States
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The schematic posted says C531 is a 47 uf 63 v cap. Confirm your unit follows that pattern.
Small electrolytics are often the first to fail. Small ratio of volume to rubber seal length. To prevent units from being broken all the time as caps fail one by one, once there is a e-cap problem I change them all. A manufacturer tends to use all the same service life rated e-caps in a product. However, I do two at a time then sound check to make sure I didn't inject a problem with a bad solder joint or incorrect part. If sound gets worse, I pretty much know where the problem would be after changing only two caps.
I buy the longest service life caps I can find so I don't have to do this job over again every 8 years, as I did when I was only allowed to buy unrated life e-caps from local TV parts stores. For example, sprague atomlytic had no service life rating. I can buy 47 uf caps rated 10000 hours service life these days. Farnell & digikey show the service life in the selector table. Many other vendors make you download the datasheet on each product and read it. Others don't tell purchasers what brand & line the cap is. I never buy e-caps from ebay amazon or alibaba. Only authorized distributors. Too much geriatric junk out there. Rubber ages sitting on the shelf or powered up in the unit.
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Last edited by indianajo; 8th June 2021 at 10:48 PM.
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Old 9th June 2021, 06:50 AM   #10
poundy is offline poundy  United Kingdom
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Nad 3020A developed problems
i had this problem with one of the 3020's i was working on and the issue went after i had replaced the caps
some of the voltage ratings in that amp are very close to the limit so i always uprate them now to a higher voltage
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