Hi all,
I'm new so please go easy on me. My NAD 3020e developed this fault a couple of years ago, that is, very low volume on both channels with distortion and smoke coming out of the unit.
It sounds like the same issue that appeared in a thread a few years ago (which reached no conclusion) although my model has different reference designators - but when you compare the schematics, I can see they are the same family of amplifier.
Here's the thread for your info:
http://www.diyaudio.com/forums/solid-state/97864-nad-3020-fried-resistors.html
My "hot" 68R resistors are R437 and R438. I've already used a multimeter to test Q405/6, Q407/8 and Q411/2. They all seem fine (some I tested in situ, others I removed to test them).
Oddly, the fuses F501/2 (F503/4 in the attached schematic) were blown. In this condition, there was no more smoke. But when I replaced them, R437/8 started smoking and glowing again.
The only other info I can offer is that one electrolytic looked melted (C517, a 330uF/63V) which I replaced with a 150uF/63V part.
Any help will be really appreciated - I loved this amp and the Cambridge Audio A1 that replaced it just doesn't cut the mustard for me (I can't afford more than that right now!)
Thanks,
Barry
I'm new so please go easy on me. My NAD 3020e developed this fault a couple of years ago, that is, very low volume on both channels with distortion and smoke coming out of the unit.
It sounds like the same issue that appeared in a thread a few years ago (which reached no conclusion) although my model has different reference designators - but when you compare the schematics, I can see they are the same family of amplifier.
Here's the thread for your info:
http://www.diyaudio.com/forums/solid-state/97864-nad-3020-fried-resistors.html
My "hot" 68R resistors are R437 and R438. I've already used a multimeter to test Q405/6, Q407/8 and Q411/2. They all seem fine (some I tested in situ, others I removed to test them).
Oddly, the fuses F501/2 (F503/4 in the attached schematic) were blown. In this condition, there was no more smoke. But when I replaced them, R437/8 started smoking and glowing again.
The only other info I can offer is that one electrolytic looked melted (C517, a 330uF/63V) which I replaced with a 150uF/63V part.
Any help will be really appreciated - I loved this amp and the Cambridge Audio A1 that replaced it just doesn't cut the mustard for me (I can't afford more than that right now!)
Thanks,
Barry
Attachments
Hi, well I ve had a 1020,(pre, now playing happily) and 3020 as well as the 2100 amp around at times, and i can tell you they are a bear to fix.
Here, i would draw your attention to the +43 v rail (sorry you know that) I would be suspicious of all the SD669's and 649's I see here.
Drivers: take 'em out, leave em out for a while. Check for heat stress, test 'em Diconnect +43V altogether. Mebbe you can repower the mains rails (32v) mebbe not
(that'll be your test for the outputs)
Now.... take a good look at the 669/649 pair that runs the +/- preamp rails, because 1-you may want to pre-amp only this unit and 2- ive found that NAD lets these run HOT, rather overheating the traces, and causing wipe-out of the filter caps (over the years) It is quite possible the 669, responsible for the +43 V rail, is fried, letting 50 V thru...
I do not, myself, feel the amp stage is worth saving-- I'm not quite sure about the 2955/3055 outputs, as I remember All-3055 in the early 3020, but I found the amp I had lacking in clarity, vis a vis the others I had around--A NAD 2100 (Lovely, but rather flakey), and the Rod elliot p3a.. (good)
Note: to use my pre (an Ebay item) I had to reflow the solder anywhere near the regulators, and replace all low-voltage Caps, and fix or abandon a panel switch, (tape/mon) and on. That and the rca's were trouble for hookups. Situation AFU, normal
Good luck-- Doug
Here, i would draw your attention to the +43 v rail (sorry you know that) I would be suspicious of all the SD669's and 649's I see here.
Drivers: take 'em out, leave em out for a while. Check for heat stress, test 'em Diconnect +43V altogether. Mebbe you can repower the mains rails (32v) mebbe not
(that'll be your test for the outputs)
Now.... take a good look at the 669/649 pair that runs the +/- preamp rails, because 1-you may want to pre-amp only this unit and 2- ive found that NAD lets these run HOT, rather overheating the traces, and causing wipe-out of the filter caps (over the years) It is quite possible the 669, responsible for the +43 V rail, is fried, letting 50 V thru...
I do not, myself, feel the amp stage is worth saving-- I'm not quite sure about the 2955/3055 outputs, as I remember All-3055 in the early 3020, but I found the amp I had lacking in clarity, vis a vis the others I had around--A NAD 2100 (Lovely, but rather flakey), and the Rod elliot p3a.. (good)
Note: to use my pre (an Ebay item) I had to reflow the solder anywhere near the regulators, and replace all low-voltage Caps, and fix or abandon a panel switch, (tape/mon) and on. That and the rca's were trouble for hookups. Situation AFU, normal
Good luck-- Doug
You have a fried driver or output transistor somewhere you must have missed it/them. I would also change that cap to the correct value or at least put another 150uF in parallel with the existing one. I have attached a schematic for the 3020e for you.
Attachments
thanks for the schematic eggontoast, I've been working from the 3020i one which appears pretty close.
i've found a couple of other threads that appear to have a similar issue as me, which point towards the output transistors and drivers/biasing as you suggest;
here:
http://www.diyaudio.com/forums/solid-state/89988-nad-amp-sound-distorted-fuses-blown.html
and here:
http://www.diyaudio.com/forums/soli...son-give-me-tip-gets-my-nad-3020-working.html
I think in my case the outputs are definintely gone (Q415 and Q417 are s/c across collector/emitter) but the drivers (Q411/Q413) and biasing transistor (Q409) appear fine. I'll go and replace these devices and see what that does
col waiting, wow, so much info in there, thank you. I got a bit lost in the middle, but it felt like generic advice to the 3020 rather than specific to my issue: I will try to internalise it!
i've found a couple of other threads that appear to have a similar issue as me, which point towards the output transistors and drivers/biasing as you suggest;
here:
http://www.diyaudio.com/forums/solid-state/89988-nad-amp-sound-distorted-fuses-blown.html
and here:
http://www.diyaudio.com/forums/soli...son-give-me-tip-gets-my-nad-3020-working.html
I think in my case the outputs are definintely gone (Q415 and Q417 are s/c across collector/emitter) but the drivers (Q411/Q413) and biasing transistor (Q409) appear fine. I'll go and replace these devices and see what that does
col waiting, wow, so much info in there, thank you. I got a bit lost in the middle, but it felt like generic advice to the 3020 rather than specific to my issue: I will try to internalise it!
Success!
A little more than £5's worth of components (including base and emitter resistors as suggested in the other threads) from Farnell and it's working again
It looks like I damaged one of the drivers (Q413) during debug, so I replaced it (a 2SB669A) with a BD139 which could handle the same Ic and power; it appears fine. On setting up the idling current I found the left channel (the one I'd been working on) would jump randomly. I traced this to dry joints on Q409 (which also sits on the large heatsink), probably caused by me when I was replacing the output transistors. I replaced the 68Rs with 1/4 parts, like the originals.
The only other thing is I noticed that Q508 gets hotter than Q507 (they both have small heatsinks bolted onto them). I wonder if this is related to C517 which I replaced with a 150uF/63V part (it was 330uF but I didn't have any of those). I shall replace that asap.
Many thanks for your help, this has been an enjoyable learning process!
A little more than £5's worth of components (including base and emitter resistors as suggested in the other threads) from Farnell and it's working again
It looks like I damaged one of the drivers (Q413) during debug, so I replaced it (a 2SB669A) with a BD139 which could handle the same Ic and power; it appears fine. On setting up the idling current I found the left channel (the one I'd been working on) would jump randomly. I traced this to dry joints on Q409 (which also sits on the large heatsink), probably caused by me when I was replacing the output transistors. I replaced the 68Rs with 1/4 parts, like the originals.
The only other thing is I noticed that Q508 gets hotter than Q507 (they both have small heatsinks bolted onto them). I wonder if this is related to C517 which I replaced with a 150uF/63V part (it was 330uF but I didn't have any of those). I shall replace that asap.
Many thanks for your help, this has been an enjoyable learning process!
The schematic (3020e) is a good bit different around q 505/506, so we had a case of the blind leading the blind. I still recommend making sure the preamp supply is happy, with reflowed solder and replacement electrolytics ( not the whole amp, just the major ones pertaining to the preamp +/-, (possibly also that +/- 40v supply, which is designed in an identical manner)
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