NAD 3020 Rebuild and Upgrade

[Earcraft]

Hi,

Did you use the dim bulb tester or variac when starting her up for the first time?

Did you change any transistors or resistors or was this only a recap?

I see you took the main and bias transistors out and reapplied heat paste or maybe silicone pads? Did you check that the transistors are ok while they were out?

Did you check the new caps before installing them?

Did you make sure there is no shorts between solder pads after you soldered them? Some are so very close to each other.

Did you make sure bias and dc offset are ok before connecting speakers?

I don't know how 3020As fuses work so (2 blown but you still get audio on both channels) and have no time to search for the manual but here is what I think: If you checked that the caps are installed correctly and you are positive there are no solder shorts then I would probably start by taking out the driver, bias and output caps and test them.

Ps. very small pics.

> I thought about building a DBT a while back but now I'm not sure where to get bulbs... I'm a little limited on equipment.
> I did replace resistors in the "soft-clipping" circuit with 1% films and a couple that had be corroded by the brown glue. In all cases I confirmed values of the old and new. I replaced a few diodes too because of the glue and check them out of circuit. I have also confirmed they are installed correctly.
> I did not replace any transistors. I only removed the main transistors 2N3055/MJ2955 but did not check them (stupid I know). I will start here however I can only check for Short/Open with the equipment I have. I will also remove and check the bias transistors. I had to re-flow one of them because the joints were cold. Yes I used silicon pads.
> I checked as many of the caps as I could. My multimeter only tests to 100uF.
> I checked a few times but will continue to look.
> I set the Bias to 32mV (manual stated 30mV to 60mV) and got the offset to 0.1ish on both channels (Lee, Thanks for the tip on the Bourns trimmers). I was surprised the adjustment went so well once I found the blown fuses.
> I can check for shorts i guess, but I'll need to find a way to check values for the big caps. Maybe it's time for a new meter...

Attached are the full size pics. Unfortunately, the lighting sucks. I'll try again in better lighting to post later. Thanks for the help and direction.

 

[Earcraft]

Lee,
Sorry this is turning into more of a hijack than a piggy-back. Thanks for the tips, I'll start pulling the transistors now. I'll start a new thread if don't find the problem.

Ps. You refer to "driver" transistors, I assume you mean the two small ones attached to the sink (Q609,Q610)?

 

[ToniCH]

Ps. You refer to "driver" transistors, I assume you mean the two small ones attached to the sink (Q609,Q610)?

Make your own thread and we shall continue there. Meanwhile check these:

 

[Earcraft]

Lee,

Did you replace your pots on any of your 3020 rebuilds? I have mine working after the recap (Finally!) but the Bass, Treble, & Balance pots are too far gone... The Volume pot is the only noiseless one after cleaning...

We use conductive plastic pots at work (I don't work the bench but I hear they are great). If you did replace, I would love to know the models you used.

Cheers,

 

[AnteEB]

I'm about to do a recap of a NAD 3120 and there is a lot of great info in this thread.
I'm curious about the brown silicone pads under the transistors, do they replace the thermal paste completely? No need for anything but the silicone pads?

 

[ToniCH]

I'm about to do a recap of a NAD 3120 and there is a lot of great info in this thread.
I'm curious about the brown silicone pads under the transistors, do they replace the thermal paste completely? No need for anything but the silicone pads?

Jep.

 

[leesonic]

I'm about to do a recap of a NAD 3120 and there is a lot of great info in this thread.
I'm curious about the brown silicone pads under the transistors, do they replace the thermal paste completely? No need for anything but the silicone pads?

The 3120 is a rare beast, the 3020 without the tone or balance controls.

That's right, just the pads. They are strictly one use only, if you have to pull the transistors off again, you should use new ones.

Lee.

 

[AnteEB]

Thanks, best to order some spare ones. What about longevity and performance for these pads? Better than thermal paste?

 

[leesonic]

What about longevity and performance for these pads? Better than thermal paste?

Some people on here don't like them. Maybe they're the wrong shade of pink, or maybe it's somehow considered lazy to NOT want to get covered in heatsink grease that makes your eyes sting when you forget and rub your eye.

There are some tests out there, but to me they seem confusing. What I would like to see is a test that uses, say, a regulated power supply to light a 21w car bulb. The regulator IC or transistor would be bolted to a heatsink using different combinations of heat transfer compound such as :

1) bolting it directly to the heatsink (no grease)
2) bolting it directly to the heatsink (with grease)
3) bolting it to the heatsink with a mica washer (no grease)
4) bolting it to the heatsink with a mica washer (with grease)
5) bolting it to the heatsink with a silicone washer (no grease)
6) bolting it to the heatsink with a silicone washer (with grease)

The heatsink temperature before the test would be measured and stabilized, perhaps by putting it in the fridge before each test. The lamp would be powered by the supply for a set amount of time, and at the end of it the heatsink temperature measured. The hotter the heatsink gets, the more heat is being transferred.

If I didn't have a million other things to be doing, I would be interested in doing this test.

Lee.

 

[elicanis]

Lee,

I am curious, what was the final tab on your rebuild (minus the loving hours of labour of course)?

 

[leesonic]

I am curious, what was the final tab on your rebuild (minus the loving hours of labour of course)?

Probably less than $100. If you want to know the exact figure, I'll have to look back through my Mouser receipts.

Lee.

 

[elicanis]

Thanks Lee, I really appreciate the reply. I was just curious as to the ballpark figure, no need for the exact economics.

 

[Dandy]

The 3120 is a rare beast, the 3020 without the tone or balance controls.

That's right, just the pads. They are strictly one use only, if you have to pull the transistors off again, you should use new ones.

Lee.

I'm going through this very informative thread as I've just bought a 7020i.

I have a 3120 and just wanted to add that it does have a balance control. It's via a dual concentric pot.

 

[nemo188]

replacing 2sd669a to tip31c and 2sb649 to tip32? driver power ampli nad 3020e

bonjour
et t'il possible de remplacer
2sd669a to tip31c and 2sb649 to tip32? drivers power ampli nad 3020e??
merci!

 

[leesonic]

bonjour
et t'il possible de remplacer
2sd669a to tip31c and 2sb649 to tip32? drivers power ampli nad 3020e??
merci!

2SD669 replace with BD139
2SB649 replace with BD140

But for the drivers, you might want to use :

2SD669 replace with BD237
2SB649 replace with BD238

Lee.

 

[Binkman]

LOL Lee! parle francais en pu?

don't worry about morphing.. a lot of nad projects get no finishing replies so any posted info is always valuable regardless of model number. Glad you're around to post. good man:thmbsp:

 

[nemo188]

nad 3020e repair

bonjour
merci de votre réponse .
j'ai remplacer tout les condensateurs,avec des nichicon et panasonic
j'ai remplacer les transistors de puissance.
et probleme court-circuit sur un des mj2955 canal droit
maintenant un canal avec deux neuf et l'autre j'ai remis deux ancien le R.
j'ai remplacer les deux drivers : 2sd669a par un tip31c et 2sb649 par tip32a.
vu q'il on grillié .
bon ca fonctionne mais je trouve que le canal avec les deux tip ,les 2 puissance chauffe
trop par apport a l'autre?.
que faire pour regler ça?

ou comme vous dite c'est mieux bd140 et bd139?ca chauffera pas?

merci de votre réponse!

 

[leesonic]

bonjour
merci de votre réponse .
j'ai remplacer tout les condensateurs,avec des nichicon et panasonic
j'ai remplacer les transistors de puissance.
et probleme court-circuit sur un des mj2955 canal droit
maintenant un canal avec deux neuf et l'autre j'ai remis deux ancien le R.
j'ai remplacer les deux drivers : 2sd669a par un tip31c et 2sb649 par tip32a.
vu q'il on grillié .
bon ca fonctionne mais je trouve que le canal avec les deux tip ,les 2 puissance chauffe
trop par apport a l'autre?.
que faire pour regler ça?

ou comme vous dite c'est mieux bd140 et bd139?ca chauffera pas?

merci de votre réponse!

I'm sorry, but I do not speak (or read) French.

Lee.

 

[nemo188]

nad 3020e repair

http://www.reverso.net/translation



Hello thank you for your answer.
I have to replace quite condensers, with nichicon and panasonic I have to replace the transistors of power.
And problem short circuit on one of mj2955 right(straight) channel(canal) maintaining a channel(canal) with two nine and the other one I put back(handed) two former(old) R.
I have to replace both drivers: 2sd669a by one tip31c and 2sb649 by tip32a.
Seen q' he(it) one grillié.
Well ca work but I find that the channel(canal) with both tip, 2 power warms too much by contribution has the other one?.
That to make for regler that?

Or as you said it is better bd140 and bd139? That will warm not?

Thank you for your answer!

 

[SoundOfSound]