Nad 3020A developed problems

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Your not missing anything :) I spotted that as well but I'm just looking at the fact it works with it disconnected and that the control comes up to the expected 13 volt or so.

So the switch has to be conductive.

Erm... I know some of the resistance checks have been a bit open to interpretation shall we say ;) and so I'll put the readings down to that. Sometimes it can be difficult to get a probe to connect through flux and grime... it all comes with experience.

Peter... just swap the wires over from one side to the other and see if it works.

I was actually going to say Deoxit might be worth a try to free things up but again experience comes into play and you don't really want to be filling the mains part of the switch with anything that could cause arcing. You would have to direct it into the top part of the switch where that little spring is (not the coil spring, the other little actuator thingy in that groove... assuming it looks exactly like the picture.

Feeding time :)
 
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Okay. I won't then. If that switch is defective I don't know if it's possible to get hold of a replacement one. Should I resolder the white wire to the switch as it was or just let it be right now?

Swap them over, see if it works.

If it doesn't then leave the wire disconnected for now. Make 100% sure it can not touch any live parts accidently.

If you can't get a switch then get a 4.7meg (4.7 million ohm) resistor and solder it across C531 and leave the switch disconnected.

Definitely feeding time now ;)
 
Peter - in the last photo I posted, with the 2 yellow lines & 2 orange lines, you can relocate the wires to the 2 orange terminals, again the order doesn't matter - they're just a second set of terminals which are identical to the first set, but have never been used, so may be cleaner.

If the top (outside) of the switch is dirty, it would be worth taking a pipe cleaner and cleaning it with something like IPA, it's just possible there might be something conductive on the outside of the switch.
 
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I've swapped those wires but no change.Still no sound. I'll disconnect the white wire again. Could you give me the color code for that 4.6 meg resistor? I don't think I have any but it may be easier to look for one. Thanks

Firstly Peter... how do you feel the amp behaves with the wire left disconnected? I was just thinking a bit more on this.

Are there any problems with excess noises (bangs, thumps etc) as you turn the amp on and off with the mains switch and I'm actually thinking more of noises at switch off now.

The resistor I suggested would not actually help much with noise at switch off. When you turn the amp off the switch connects the mute circuit to the negative supply and it relies on that negative supply lasting long enough (as the caps discharge) to hold the amp in mute while the main amplifier power supply caps also discharge and the whole amp then stops functioning.

I have some other ideas on the switch itself. You say it is very dirty. How confident are you of putting some paper towel under and around that first part of the switch, then hold the amp vertically on its front and give that switch area a good clean with your spray. Work the switch on/off many many times and use the paper to absorb the gunge. Flood that part of the switch with cleaner but keep the amp vertical to stop it running into the mains area of the switch.

(By disconnecting the switch and also you confirming the voltage is correct on D507 we have proved beyond doubt that leakage is the problem)
 
I'd have hoped for a better result using the other pair of terminals, but it is what it is.

The original Alps switch is long obsolete, but does occassionally turn up on the usual auction site, normally well over-priced. The following is an example of a slightly older version of the same switch - which I think may have a lower mains current rating than yours, but I'm not sure (?): Alpes SDU3P Power Switch TV-3 - NAD realiste Marantz Concept 16.5 Recepteur Sanyo | eBay
The only suitable 'new' replacement switch that I'm aware of would be the following: Commutateur: ES0210 INTERRUPTEUR DE RESEAU / 6A / 250V = KONIG 6571 / 16571 / CRP2147 / CBP3011... (full specs are available at Mouser - https://www.mouser.co.uk/ProductDetail/CK/NE1839EE?qs=U2%2BV/zDE79GIQgtl4FQ0uQ==). This switch is certainly suitable, and is almost a drop-in replacement - you would need to transfer the original NAD switch mounting 'plate', which is fiddly but straightforward to do, and reposition the wiring a little (it's physically smaller than the original NAD switch).
 
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i take these apart and clean them, and quite successfully.Ive managed to take apart every switch in those amps and clean the contacts, they are on little 'u' shaped sliders.They are very fiddly, but it is possible.
Ive tried getting alternatives but the probelm i found is the distance from the switch flange to the tip of the knob stem, they tend to be close, but not exact, and this ends up making the switch protrude from the front casing.
quite often, because the plastic is quite brittle, the stems snap off, so i remove them, dril out the stem and switch with a 1mm drill and glue the 2 parts back together with a cut to size panel pin glued in-works a treat.

give it a go though you might just get lucky.
 
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Thank you again for helping me on this.


Now with the white wire disconnected the amp sounds like before. No thumps or bangs on start up. There is a very short growl for a couple of seconds, that's it. When I turn it off it goes silent immediately. As for cleaning the switch the best would be to take it out as there isn't much room there to get to it. But that's a lot of work having to desolder then re solder all those wires etc. I've already tried to clean it a little but over the decades it has accumulated a lot of dust inside the amp which turns into grime. Perhaps I should just buy a cleaner that penetrates and evaporates immediately. I think 3 in 1 does something like that but not sure. Deoxit tends to lubricate more which produces grime too. It doesn't evaporate.
As for that resistor, seems pretty difficult to get such a high value that's small as well
 
Firstly Peter... how do you feel the amp behaves with the wire left disconnected? I was just thinking a bit more on this.

Are there any problems with excess noises (bangs, thumps etc) as you turn the amp on and off with the mains switch and I'm actually thinking more of noises at switch off now.

The resistor I suggested would not actually help much with noise at switch off. When you turn the amp off the switch connects the mute circuit to the negative supply and it relies on that negative supply lasting long enough (as the caps discharge) to hold the amp in mute while the main amplifier power supply caps also discharge and the whole amp then stops functioning.

I have some other ideas on the switch itself. You say it is very dirty. How confident are you of putting some paper towel under and around that first part of the switch, then hold the amp vertically on its front and give that switch area a good clean with your spray. Work the switch on/off many many times and use the paper to absorb the gunge. Flood that part of the switch with cleaner but keep the amp vertical to stop it running into the mains area of the switch.

(By disconnecting the switch and also you confirming the voltage is correct on D507 we have proved beyond doubt that leakage is the problem)




Just read your post, thanks. So the resistor helps only on start? At this point it doesn't make any noise on switch off. I'll try your cleaning suggestion but I'll get a different cleaner. As I've said I think the Deoxit produces even more gunk mixing with the dust.
 
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If you are happy with the overall result of leaving it off then that is a valid fix for you :)

The resistor would have ensured the cap discharged when the amp was off and so it would get the full mute effect at power on... but you say it growls :D

It is possible that the mechanics of the switch are such that the contacts of the mains section and the mute section are not exactly timed together... by design. So as you press it on the mains voltage might be applied before the mute contacts open.

If you can remove the switch, even if you don't unsolder it, then it would be worth saturating that front part with cleaner.

Don't use anything other than a recognised switch cleaner, some products can actually attack and soften plastics over months and years, a problem I know only to well from working in the repair trade.
 
Thank you very much, I'll sure consider it. I'll try cleaning it first as Mooly suggested it then if no good I'll take it out and re clean it. There is the replacement option too but I am not too sure about that especially if you have to drill and glue but I'll check the Ebay or the other source as Goldie suggested it. If the amp functions as is I'll probably just let it be after some cleaning efforts.