Much Magic Smoke - But Amp still playing - NAD 3030 - UK Vintage Radio Repair and Restoration Discussion Forum

SeanStevens · 12th Aug 2020, 3:52 pm

While listening to music this afternoon I heard a little crackling sound behind me (I love crackling, but not this kind).

A plume of smoke was curling from the NAD amp - music still merrily playing. I isolated the supply pronto.

I've ripped the cover off and was about to post photos of the fire damage - but there isn't any visible.

I've check the board, expecting a fried capacitor or resistor.... nothing.

The transformer seems to smell the worst, but I'm not sure it is the source of the smoke.... not a lot to go on ladies and gents.

SEAN

Welsh Anorak · 12th Aug 2020, 4:15 pm

The most common cause of this sort of thing - hopefully - is the snubber capacitor across the mains with the most common offender being the RIFA semi-transparent ones. However I don't think your NAD uses them, though I may be wrong. If it does, then there are many threads on the forum talking about them - with good reason!
I'm afraid the only way to determine what's going on is to power up with one hand on the switch. Leave the speakers disconnected for this just in case.
Did you notice any degradation in the music? Inspect the various resistors in the output stage feed - these can cook, but usually don't emit all that much smoke and the affected channel dies.

Humber888 · 12th Aug 2020, 4:21 pm

As Glyn states, always suspect any Rifa or Wima capacitor across the mains or a Schaffner mains filter, especially if the amp was still playing. Hopefully it's not the transformer.

Mike

DMcMahon · 12th Aug 2020, 4:43 pm

Looking at the schematic it shows 2 capacitors, one each across the switched live and neutral connections at the On/Off switch. Assume these are some sort of spark suppressor, they are identified as 4700P, which I assume is 4,700pF which seems quite a low value in this application.

Cannot see them listed in the parts list.

If one or both have burnt up and gone open circuit then the amp will still work as normal.

David

Stockden · 12th Aug 2020, 4:44 pm

This is the mains input circuitry as shown in my copy the service manual. If it's correct (and if I've understood it correctly) there should be no voltage across the capacitor when the amplifier is switched on.

Edit - Crossed with David. It seems there may be different versions of the circuit.

Hugh

DMcMahon · 12th Aug 2020, 4:57 pm

Yes agreed no voltage across the capacitors once switched fully on, so theoretically should not go up in smoke while running, the 3020 circuit is slightly different.

Looking elsewhere 4,700pF disc ceramics are sometimes used as suppressors.

David

Goldie99 · 12th Aug 2020, 5:21 pm

They're 4700pF, 400VAC ceramics in mine (NAD 3030), one across the on/off switch 'live', one across the switch 'neutral', and they're close to an inch across - so, although I doubt it, it should be pretty easy to see if they're burnt.

Alan

paulsherwin · 12th Aug 2020, 5:23 pm

Happened to mine years ago. Everything carried on working, I couldn't see any signs of distress, so I just ignored it. That amp is in line for a major overhaul so I'll investigate it further then.

SeanStevens · 12th Aug 2020, 5:44 pm

Quote:

Originally Posted by Welsh Anorak

The most common cause of this sort of thing - hopefully - is the snubber capacitor across the mains with the most common offender being the RIFA semi-transparent ones.

Dear Welsh Anorak, you win!

I have attached a photo the component which is EXACTLY what you said it was and even semi-transparent. Thank the lord it was not the transformer!

I'll replace that cap with another x-rated one - thanks again:

Now, onto a related issue - the on/off switch has never worked and now I have it 'prone' I should ideally replace it.

Any ideas where one would get a switch like that photographed please . . a big ask on a hot day - but this is why the Forum works!!!

SEAN
Thanks in advance - and to all that said Rifa!

Station X · 12th Aug 2020, 5:46 pm

Sounds like a problem I had with a Cambridge P50 which I repaired. I was listening to it when there was an almighty bang, loads of smoke and what smelled like a burning transformer. Turned out that a Rifa connected in series with a resistor across the mains had gone short-circuit vapourising the resistor.

The amp carried on working once the 3 fuse in the mains plug was replaced.

G6Tanuki · 12th Aug 2020, 6:16 pm

The switch is probably clagged-up with old dried-out contact-grease or similar: rather than replacing it you have nothing to lose by buying a can of 'brake cleaner' spray from the local car-parts place, putting the switch in a small jam-jar, squirting-in a load of the cleaner then screwing the lid on and leaving for a few days so the cleaner can do its thing on the cruddy grease.

Then take the switch out and use more cleaner squirted directly into any openings/apertures you can see on the switch, then 'work' it vigorously on-and-off, then more squirting!

it takes a lot to dislodge decades of dust that have settled into the grease.

DMcMahon · 12th Aug 2020, 6:58 pm

Quote:

Originally Posted by SeanStevens

Quote:

Originally Posted by Welsh Anorak

The most common cause of this sort of thing - hopefully - is the snubber capacitor across the mains with the most common offender being the RIFA semi-transparent ones.

Dear Welsh Anorak, you win!

I have attached a photo the component which is EXACTLY what you said it was and even semi-transparent. Thank the lord it was not the transformer!

I'll replace that cap with another x-rated one - thanks again:

Now, onto a related issue - the on/off switch has never worked and now I have it 'prone' I should ideally replace it.

Any ideas where one would get a switch like that photographed please . . a big ask on a hot day - but this is why the Forum works!!!

SEAN
Thanks in advance - and to all that said Rifa!

So where was the RIFA fitted ? on the underside of the board as photo 2, if so looks like it was was connected across Live and Neutral (which is not shown in the schematic), I guess the 2 green devices in photo 1 are the 4,700pF caps.

DAVID

AC/HL · 12th Aug 2020, 8:52 pm

Quote:

Originally Posted by Stockden

It seems there may be different versions of the circuit.

It would seem so, as with a recent Quad thread, same fault, same variance. EMC compliance?

Bazz4CQJ · 12th Aug 2020, 9:49 pm

Quote:

Originally Posted by paulsherwin

Happened to mine years ago. Everything carried on working, I couldn't see any signs of distress, so I just ignored it. That amp is in line for a major overhaul so I'll investigate it further then.

I have a NAD 3020 reciever, which I bought new in the 1980's and I'm hoping that it will "see me out"! It's working perfectly, and has never emitted any smoke, but I do sometimes wonder whether some "preventive maintenance" would be a good idea, or to stick to the path of "if it ain't broke..."?

My NAD cassette deck died some months ago (complex issues in the transport mechanism which hours of effort failed to resolve), but I managed to substitute that with a Harmon Kardon TD392, bought via ebay but from a local seller.

B

SeanStevens · 13th Aug 2020, 7:51 am

Quote:

Originally Posted by DMcMahon

So where was the RIFA fitted ? on the underside of the board as photo 2, if so looks like it was was connected across Live and Neutral (which is not shown in the schematic), I guess the 2 green devices in photo 1 are the 4,700pF caps.

It was across the first two holds as you say. The green gremlins are marked 250v, 1k. (resistors?)

I will treat the switch, but it is broken at the front (post itself is snapped) and it is currently broken in the 'on' position. I may get unlucky and get it to move from 'on' to permanently 'off'!

Does the switch look generic to you people?

SEAN

Welsh Anorak · 13th Aug 2020, 9:53 am

I'll have a look if I have something similar.
If you have repaired NADs you'll know the schematic serves as a general guide as the unit you're working on will be significantly different!
I'll claim my prize later...

peter_sol · 13th Aug 2020, 10:02 am

Hi Sean.

I have a switch which looks like that.
It looks used but you are welcome to it FOC.
I assume you have the knob.
If you PM me with your details I'll pop it in the post.
Regards

Peter.

Goldie99 · 13th Aug 2020, 10:03 am

Not sure on the exact details for the 3030 switch, but this may be close:

https://www.rapidonline.com/Power-PC...efe5667219c31a

cathoderay57 · 13th Aug 2020, 10:11 am

Hi Sean, I have the 2 push switches shown below. I guess size is important

so I included the ruler. End-on the max height of the blue-tipped switch is 24mm; the hole spacing on the front bracket is 18mm. The other one measures height of the black bracket 15mm, white part 8mm (including contacts 17mm). Mounting holes 23mm. Are either of these any use? Cheers, Jerry

G6ONEDave · 13th Aug 2020, 10:29 am

The 2 green gremlins are capacitors and the 1K suggests that they are 1000pf or 0.001uf if you prefer the uf value.

12th Aug 2020, 3:52 pm	#1
SeanStevens Octode Join Date: Sep 2009 Location: Bath, Somerset, UK. Posts: 1,033	Much Magic Smoke - But Amp still playing - NAD 3030 While listening to music this afternoon I heard a little crackling sound behind me (I love crackling, but not this kind). A plume of smoke was curling from the NAD amp - music still merrily playing. I isolated the supply pronto. I've ripped the cover off and was about to post photos of the fire damage - but there isn't any visible. I've check the board, expecting a fried capacitor or resistor.... nothing. The transformer seems to smell the worst, but I'm not sure it is the source of the smoke.... not a lot to go on ladies and gents. SEAN __________________ There are only 10 types of people, those who understand the binary system, and those who don't.

12th Aug 2020, 4:15 pm	#2
Welsh Anorak Dekatron Join Date: Apr 2005 Location: North Wales, UK. Posts: 6,918	Re: Much Magic Smoke - But Amp still playing - NAD 3030 The most common cause of this sort of thing - hopefully - is the snubber capacitor across the mains with the most common offender being the RIFA semi-transparent ones. However I don't think your NAD uses them, though I may be wrong. If it does, then there are many threads on the forum talking about them - with good reason! I'm afraid the only way to determine what's going on is to power up with one hand on the switch. Leave the speakers disconnected for this just in case. Did you notice any degradation in the music? Inspect the various resistors in the output stage feed - these can cook, but usually don't emit all that much smoke and the affected channel dies. __________________ Glyn www.gdelectronics.wales

12th Aug 2020, 4:21 pm	#3
Humber888 Heptode Join Date: Jul 2012 Location: Bromley, London, UK. Posts: 702	Re: Much Magic Smoke - But Amp still playing - NAD 3030 As Glyn states, always suspect any Rifa or Wima capacitor across the mains or a Schaffner mains filter, especially if the amp was still playing. Hopefully it's not the transformer. Mike

12th Aug 2020, 4:43 pm	#4
DMcMahon Dekatron Join Date: Apr 2019 Location: Worthing, West Sussex, UK. Posts: 6,600	Re: Much Magic Smoke - But Amp still playing - NAD 3030 Looking at the schematic it shows 2 capacitors, one each across the switched live and neutral connections at the On/Off switch. Assume these are some sort of spark suppressor, they are identified as 4700P, which I assume is 4,700pF which seems quite a low value in this application. Cannot see them listed in the parts list. If one or both have burnt up and gone open circuit then the amp will still work as normal. David

12th Aug 2020, 4:44 pm	#5
Stockden Heptode Join Date: Mar 2008 Location: Forest of Dean, Gloucestershire, UK. Posts: 648	Re: Much Magic Smoke - But Amp still playing - NAD 3030 This is the mains input circuitry as shown in my copy the service manual. If it's correct (and if I've understood it correctly) there should be no voltage across the capacitor when the amplifier is switched on. Edit - Crossed with David. It seems there may be different versions of the circuit. Hugh Attached Thumbnails Last edited by Stockden; 12th Aug 2020 at 4:48 pm. Reason: spelling!

12th Aug 2020, 4:57 pm	#6
DMcMahon Dekatron Join Date: Apr 2019 Location: Worthing, West Sussex, UK. Posts: 6,600	Re: Much Magic Smoke - But Amp still playing - NAD 3030 Yes agreed no voltage across the capacitors once switched fully on, so theoretically should not go up in smoke while running, the 3020 circuit is slightly different. Looking elsewhere 4,700pF disc ceramics are sometimes used as suppressors. David

12th Aug 2020, 5:21 pm	#7
Goldie99 Heptode Join Date: Jul 2014 Location: Boston, Lincolnshire, UK. Posts: 995	Re: Much Magic Smoke - But Amp still playing - NAD 3030 They're 4700pF, 400VAC ceramics in mine (NAD 3030), one across the on/off switch 'live', one across the switch 'neutral', and they're close to an inch across - so, although I doubt it, it should be pretty easy to see if they're burnt. Alan

12th Aug 2020, 5:23 pm	#8
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,943	Re: Much Magic Smoke - But Amp still playing - NAD 3030 Happened to mine years ago. Everything carried on working, I couldn't see any signs of distress, so I just ignored it. That amp is in line for a major overhaul so I'll investigate it further then.

12th Aug 2020, 5:46 pm	#10
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: Much Magic Smoke - But Amp still playing - NAD 3030 Sounds like a problem I had with a Cambridge P50 which I repaired. I was listening to it when there was an almighty bang, loads of smoke and what smelled like a burning transformer. Turned out that a Rifa connected in series with a resistor across the mains had gone short-circuit vapourising the resistor. The amp carried on working once the 3 fuse in the mains plug was replaced. Attached Thumbnails __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

12th Aug 2020, 6:16 pm	#11
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 13,998	Re: Much Magic Smoke - But Amp still playing - NAD 3030 The switch is probably clagged-up with old dried-out contact-grease or similar: rather than replacing it you have nothing to lose by buying a can of 'brake cleaner' spray from the local car-parts place, putting the switch in a small jam-jar, squirting-in a load of the cleaner then screwing the lid on and leaving for a few days so the cleaner can do its thing on the cruddy grease. Then take the switch out and use more cleaner squirted directly into any openings/apertures you can see on the switch, then 'work' it vigorously on-and-off, then more squirting! it takes a lot to dislodge decades of dust that have settled into the grease.

13th Aug 2020, 9:53 am	#16
Welsh Anorak Dekatron Join Date: Apr 2005 Location: North Wales, UK. Posts: 6,918	Re: Much Magic Smoke - But Amp still playing - NAD 3030 I'll have a look if I have something similar. If you have repaired NADs you'll know the schematic serves as a general guide as the unit you're working on will be significantly different! I'll claim my prize later... __________________ Glyn www.gdelectronics.wales

13th Aug 2020, 10:02 am	#17
peter_sol Octode Join Date: Aug 2003 Location: Welwyn Garden City, Herts. UK. Posts: 1,906	Re: Much Magic Smoke - But Amp still playing - NAD 3030 Hi Sean. I have a switch which looks like that. It looks used but you are welcome to it FOC. I assume you have the knob. If you PM me with your details I'll pop it in the post. Regards Peter.

13th Aug 2020, 10:03 am	#18
Goldie99 Heptode Join Date: Jul 2014 Location: Boston, Lincolnshire, UK. Posts: 995	Re: Much Magic Smoke - But Amp still playing - NAD 3030 Not sure on the exact details for the 3030 switch, but this may be close: https://www.rapidonline.com/Power-PC...efe5667219c31a

13th Aug 2020, 10:11 am	#19
cathoderay57 Nonode Join Date: Oct 2017 Location: Bristol, UK. Posts: 2,384	Re: Much Magic Smoke - But Amp still playing - NAD 3030 Hi Sean, I have the 2 push switches shown below. I guess size is important so I included the ruler. End-on the max height of the blue-tipped switch is 24mm; the hole spacing on the front bracket is 18mm. The other one measures height of the black bracket 15mm, white part 8mm (including contacts 17mm). Mounting holes 23mm. Are either of these any use? Cheers, Jerry Attached Thumbnails

13th Aug 2020, 10:29 am	#20
G6ONEDave Octode Join Date: Dec 2019 Location: Owston Ferry, North Lincolnshire, UK. Posts: 1,701	Re: Much Magic Smoke - But Amp still playing - NAD 3030 The 2 green gremlins are capacitors and the 1K suggests that they are 1000pf or 0.001uf if you prefer the uf value.