nad 3020e - distortion both channels

J

johnlon

New Member
nad 3020e has started distortion on both channels
was fine before
given both channels affected is this likely a PSU issue?
psu caps?

any advice on fault finding thanks

video of problem
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(I'm fine with a meter or a scope or soldering iron)
 
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For starters, I would give the underside a really good looking at with a magnifying glass. I've repaired quite a few NADs and they are riddled with bad solder joints. Pay close attention to the joints around power regulator transistors. (The ones with screwed on heatsinks). Check for discoloured or burnt out components too.
 
I totally agree with the above. I would suspect an issue in the regulated portion of the power supply. Voltages are in the service manual.

Screen Shot 2026-02-08 at 9.22.01 PM.png
 
if it's a PSU issues (which I do suspect) would the distortion disappear somewhat at low volumes?
just curious as a problem identification check.

can ask my son to try that test, but just curious.

in any case he's coming back from uni this weekend and is swapping his crackly 3020e with my repaired 3020 series 20 which gives me a bit of fun fixing his amp.
 
also if I'm pulling this thing about then are there some obvious precautionary replacements.or upgrades. Ie usual suspects like specific caps or underrated components or need for a heatsink etc etc.

I don't like doing pointless work but sensible precautions make sense to me.

his is the 3020e

oh and maybe some diagnostics worth doing while case is off?

and is there anything in there that doesn't like a dose of IPA (not the beer) during cleaning?
 
If you have a voltage that's low or missing, it may be causing distortion in the power amp. That would not change with lower volume. First step would be to check the supply voltages. Second step is build a dim bulb tester if you don't already have one.

There likely are some caps that need replacing and maybe some other parts too. NAD didn't use the best parts back then. They were hitting a price-point that college kids could afford. That's when I bought my first 3020. As far as checking caps and transistors, one of the $20 component testers can get you started, but with these you may have to pull the caps to test them. Spend another $10-$15 and you can get an LCR tweezer tester that I hear can measure caps in circuit, but they don't test transistors. Neither of these are top quality, but fine for occasional use.

Screen Shot 2026-02-09 at 5.45.28 PM.pngScreen Shot 2026-02-09 at 6.21.54 PM.png
 
johnlon said:
if it's a PSU issues (which I do suspect) would the distortion disappear somewhat at low volumes?
just curious as a problem identification check.

can ask my son to try that test, but just curious.

in any case he's coming back from uni this weekend and is swapping his crackly 3020e with my repaired 3020 series 20 which gives me a bit of fun fixing his amp.
Click to expand...
We can break it down a bit to isolate whereabouts the fault is. For starters we know that the distortion is on both channels: this implies something that is common to both channels. - that pushes my thoughts to power supply and power regulation.
Next we need to isolate if it's in the pre amplifier section or the power. You say that your son is bringing his around. This makes it very easy to test:
You'll need two pair of RCA interconnects. And the ability to have both his known good one and yours powered up together.
Remove the U-links from the back of both amps and (using the interconnects) cross patch the preamp of yours to the power amp of his. Have speakers or headphones plugged in to his. While playing music, is the distortion present? If not, you have proved that the pre section of your is ok. Next swap the interconnects arround so that you are using the pre amp of his and the power amp of yours. (Speakers or headphones plugged in to yours) Is there distortion while playing now? if so that means you've proved the distortion is in the power amp section of yours. If you get distortion on both tests, that pushes the fault definitely in to the pwoer regulation section to my mind. Check your voltages as per the schematic. (noting whether you are on 4Ω or 8Ω selection)
Place very close attention to the regulator transistor soldering. All I have worked on had heat stressed solder.
 
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@DatunWalnut mine is the series 20 original with the u link. his is the 3020e with an integrated preamp without the link if I recall correctly. not sure if there's an injection point after the pre amp?

but your suggestion is interesting. on a 3020e there is I phono input and of course line level inputs for cd,aux etc

do the line level inputs go via the preamp or after it? dunno if that helps all for fault finding?

I believe the recording made was with an input to the line level not to phono from his deck.
 
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It's a shame they decided to omit the Pre Out / Power Amp In connectors on this version. There is gain & tone control circuitry before the power amp stage that all inputs pass through.
Screen Shot 2026-02-12 at 6.17.23 AM.png
 
A bit late to the party on this one. As others have suggested, test the power supply and verify you are getting the correct voltages. As well as the power supply shown earlier in this thread, there is another less-regulated supply that powers the output transistors that needs to be checked as well.

With regards to the pre/power amp split. Points X and Y, or A and B in the diagram above would be where a pre/power amp split would have been. Those FETs (can't read the number, but 2SJ111) are the muting FETs for the preamp. If you can physically split X & Y (or A & B) by removing a wire, you can split the preamp and power amp, and test them individually.

Lastly, there is a procedue on here showing how to test transistors using just a multimeter set to the diode range. I can't seem to find it now, but from what I remember, you put one meter lead onto the Base of the transistor, and you should get a reading measuring to the Emitter and Collector. Like the transistor is acting like two diodes. Swap the red and black leads, and the transistor won't conduct. Or shouldn't, unless it's shorted.
 
johnlon said:
@DatunWalnut mine is the series 20 original with the u link. his is the 3020e with an integrated preamp without the link if I recall correctly. not sure if there's an injection point after the pre amp?

but your suggestion is interesting. on a 3020e there is I phono input and of course line level inputs for cd,aux etc

do the line level inputs go via the preamp or after it? dunno if that helps all for fault finding?

I believe the recording made was with an input to the line level not to phono from his deck.
Click to expand...
leesonic said:
A bit late to the party on this one. As others have suggested, test the power supply and verify you are getting the correct voltages. As well as the power supply shown earlier in this thread, there is another less-regulated supply that powers the output transistors that needs to be checked as well.

With regards to the pre/power amp split. Points X and Y, or A and B in the diagram above would be where a pre/power amp split would have been. Those FETs (can't read the number, but 2SJ111) are the muting FETs for the preamp. If you can physically split X & Y (or A & B) by removing a wire, you can split the preamp and power amp, and test them individually.

Lastly, there is a procedue on here showing how to test transistors using just a multimeter set to the diode range. I can't seem to find it now, but from what I remember, you put one meter lead onto the Base of the transistor, and you should get a reading measuring to the Emitter and Collector. Like the transistor is acting like two diodes. Swap the red and black leads, and the transistor won't conduct. Or shouldn't, unless it's shorted.
Click to expand...
 

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thanks yes the other way round of course. the emitter current on an npn is the sum of the base and collector.

was standing in a petrol station on the M4 when I wrote that.
 
ok just starting to look at it.

other symptom is that the sound volume is capped at a low level .

one volume knob.is eg 90 degrees it gets no louder at all. no effect at all.

like there's no juice to squeeze on the power
 
PCB is marked

NAD3020E
NAD3020PE
5553125800 "w-08"
TATUNG TT-294-v0

Looking at this doco it seems to be labelled W-00 and there are some labelling differences on the fuse section.

I now realise that they are a little sloppy in the manufacture - see attached.
The fuses are on a little board and there are two pairs of fuses and each has an associated cap.
The diagram shows f503/504 and C503 wheream I got confused for a couple of hours cos I couldn't locate the fuses and cap
my amp uses which are f501/502 and C502. I then noticed them on the NAD3020PE circuite diagram which uses all 4 fuses and caps.
But the 3020E only uses half the fuse board and the assemblers obiously used the other half that isn't on the E schematic at all.
Hey ho.

! The two fuses F503/504 (or alt f501/502) are blown.

I didn't notice if these were blown before I started work as I didn't even pay attention to that little board until I'd inspected the back of the main one (which looks ok).
But then I noticed that a cap C502 (see below) was lifted, and so forgot to check the fuses before investigating c502.
So I don't know it those fuses were blown by me or the underlying fault.

Also C502 which bridges the output of those two fuses (coincidentally ?) wasn't soldered properly.
One leg was basically floating, possibly in contact intermittently, so I attached that properly.

However, I need to get two fuses to test more.

Additionally C502 measures as 10nF out of circuit which seems tiny but it has a high resistance so isn't a short. The schematic indicated 0.1 but no units.
UPDATE: Found Schematic for 3020i and it shows this as 10nf https://akdatabase.org/AKview/albums/userpics/10007/NAD 3020i 3225PE Service Manual.pdf

Also - the discrete bridge rectifier diodes are intact.

--

The voltage across the dead fuses is 44v AC.
Neither of the rail coming out of the discrete rectifier are shorted to ground.

Both big caps read about 4800uf

--

All 4 power transistors still look like transistors, diodes drops where there should be diode drops.

? However, correct me if I'm wrong but I can't test these in circuit using the opposite multimeter probes - where out of circuit these should read open.
If I try this on my multimeter then on the npn the voltage creeps up to 2v then my meter reads OL.
Maybe its pointless?? let me know.

--

npn Q411 ok
www.alldatasheet.com

2SD669 datasheet(1/7 Pages) HITACHI

2SD669, 2SD669ASilicon NPN EpitaxialApplicationLow frequency power amplifier complementary pair with 2SB649/AOutline1. Emitter2. Collector3. BaseTO-126 MOD1 Datasheet search, datasheets, Datasheet search site for Electronic Components and Semiconductors, integrated circuits, diodes, triacs and...
www.alldatasheet.com

pnp Q413 ok
www.alldatasheet.com

2SB649 datasheet(1/8 Pages) HITACHI

2SB649, 2SB649ASilicon PNP EpitaxialApplicationLow frequency power amplifier complementary pair with 2SD669/AOutline1. Emitter2. Collector3. BaseTO-126 MOD1 Datasheet search, datasheets, Datasheet search site for Electronic Components and Semiconductors, integrated circuits, diodes, triacs and...
www.alldatasheet.com

npn q412 ok

pnp q414 ok

---
bd139 pnp ...

pnp q410 B/C is a 0.6v but B/E is 0.18v (116ohm) DEAD MAYBE NOT?
pnp q409 B/C is 0.6v but B/E is 0.18v (116ohm) DEAD MAYBE NOT?

BUT there are 2 resistors from B to E, a 100 (r441) and a 39 (r445) so OK ????
At least there is no short ?!

---

D406/406 ok

---

bd139 pnp ...

Q407 ok
q408 ok

---

pnp bc556B BC556 PNP Transistor

q405 0.7v ok
q406 0.7v ok

====

npn bc550c base in middle

q401 0.7v ok
q402 0.7v ok

pnp bc556b

q403 0.7v ok
q404 0.7v ok

----

d401/401 ok

d403/404 ok

----

d801 ok
d803 ok

d802 ok
d804 ok
d805 ok
d806 ok

----

q5XX transistors all ok

----

q301 ok
q302 ok
q303 ??? is this labelled wrong in the schematic?? B and E seem transposed on the little image on schematic vs my measurements and datasheets
q304 ok ?
 

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Just a thought: Another point of commonality is the mute fets on the output of the preamp (Q309 & 310). Try scoping the Source of both of them to a 1Khz square wave and compare it with the Drain. if the signal diode or the 22uF/100v cap were going faulty, it might cause noise to be injected at that point.
 
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