NAD3020 Series 20 (repair/update)

[Joe_music]

So here we are, I've been working on my NAD3020 (later 80' version with the 4 power caps in the center) for fews weeks now. Collecting info on AK thread and some people that I've been happy to received some help in inbox, thanks to them, and with my electric knowledge I did a full recap and I'm diagnostic the issues. I'll post the infos I've got to help other person who is looking to work on this amp. In the mean time I'll put some link of threads I have read and collected my infos from

NAD3020 rebuild and update
Another NAD3020 rebuild and update
NAD3020 rebuild

Rewind of how was the amp when I bough it (for 40$cad). Photos attached.

No matter the sounds level the speaker where clipping (popping sounds) really really loud and all the led power were all lit up. The amp was basically not working, there we also a big pop sounds when turned on and off.

 

[Joe_music]

First step was to find the right electrical schematic since the model have changed fews times.. HiFiEngine is a pretty good database for manual and schematic, I've found the manual that fits my amp there.

My version is " service manual - fmmech "

As you may see online and on AK, a recap is a commun change on old equipment. I've look at all the capacitors physically and see if they correspond to the one listed in the manuel.. they are!! My amp was basically factory since I've not seen any sign of mods to it.

After making the list with voltage, impendance and where they belong. I went to buy all Nichicon capacitors and took care to chose right one depending on where they were on the circuit. I bought from Mouser Electronics website. I did include the power switch and a new Quencharc.

The board was dirty so I did cleaned off as I was getting some space when removing old component.

 

[Joe_music]

Problem was unfortunately not solved with only a recap, I had to dig in a little bit more. After testing the phono preamp only I could isolated this part of the circuit as working good.

I stepped into setting the bias and offset with variable resistors (forgot to include that I ordered those with the caps since it is good to do it).

I was able to set the bias at 30mV on one channel but not on the other one, And i'va got crazy high DC offset at the outputs... so I stopped there and went to remove all 4 outputs transistors and drivers, with all other transistors that are the sames as the drivers.

If you are having trouble understanding how to set bias and offset leesonic explained it well on his thread (first one I've listed) on page 3.

Found out after testing all of these that I had Q611 and Q612 dead. So I went to Mouser to order new transistors, silicon pads for transistors on the heatsink since I removed the original mica washer.

Hopefully this could be getting this amp to work properly so I can listen to it for the first time. Still waiting for component to arrive.

 

[seedbread]

Thank you for this thread its been invaluable in starting the process of a recap for my 3020, I have the same later 80's model as you but I am struggling to find the schematics and hifi engine won't allow me to register to download the manual you have linked, is there anyway you could link the manual directly or send the manual to me?

I am also having a problem with clipping when the amp is powered on have you been able to fix this yet?

Hope by now you have got all the parts and been able to listen to the amp.

 

[Guido57]

It has been posited that HiFi Engine is not accepting new registrations. I haven't found anything definitive on their FAQ or request pages about this issue other than the precautions the site has taken to protect itself from bots.

 

[Joe_music]

Thank you for this thread its been invaluable in starting the process of a recap for my 3020, I have the same later 80's model as you but I am struggling to find the schematics and hifi engine won't allow me to register to download the manual you have linked, is there anyway you could link the manual directly or send the manual to me?

I am also having a problem with clipping when the amp is powered on have you been able to fix this yet?

Hope by now you have got all the parts and been able to listen to the amp.

Hi, yes I could send you the schematic that I have, hopefully you'll have the same exact version of amp!

i had replaced the two transistors, put back everything in place and first thing first bias ajustement was succesful! Did adjust it around 30.5 to 31mV.

I did power up the amp yesterday, without speakers pluged-in to the terminal at idle everything seems fine, I still have a DC offset not correct.. The weird part is that when speakers were pluged in, the loud clipping sounds was back but without speakers the led power indicator didn't lit up.

Still have some work to do.. might look for every piece in after the "normal in" to see if I found sonething.

 

[Joe_music]

After few times of looking in the amp and taking measurements, I was comparing the voltage all around the circuit written in the manual vs mine. Came across a few that were not matching.. especially the +- 30,5V on the outputs transistors.

Find out that I have like +60V on Q615-616.. and went to find the source. From F3, F4 to the bridge rectifier (BO901) to main cap (C901..4) with two other caps (C921-22)...


So, my reading was around 60V like I said and -3.2V on the other hand... Took out the bridge rectifier to test it.. Seems fine, that is my issue now because I would assumed it was my issue..

When I pulled out the bridge, all diode inside tested good and even voltage looks good :
+ and gnd (frame) : +23.3 Vdc
- and gnd : -23 Vdc
+ and - : 45 Vdc

I'll continue my search.. If anybody could have an idea feel free to share!

Side note : The weird sounds when turning on the amp was not there when the bridge removed, might be the issues or only the power for the chip is coming from the bridge

 

[Joe_music]

So I had a audio signal generator and a oscilloscope from my collegue and I was trying to find the problem after taking all the mesurement point on the schematic.. with a 30Hz signal the output transistors was switching like crazy and eventually broke the bridge rectifier.. will by another one from mouser soon enought.

I don’tknow if my output transistors could be the cause of my problem but I was trying to have some info about genuine part and I'm sure 100% that I have so considering mine have a Q before the s/n.. but maybe I would give it a try to change them since I had 60Vdc and -3Vdc from the power supply..

I saw @leesonic used ST 2N3055 and MJ2955, I'm trying to find replacement option here. I think I have found some ON semi, or I have some MJ21195/6G from ON Semi in my mouser basket. Maybe Lee have some tips on these.

 

[leesonic]

If you can't find 2N3055/MJ2955 at Mouser or Digikey, you can use MJ15015 / MJ15016. But Mouser seems to have both flavors in stock as of today.

 

[Joe_music]

Thanks Lee, I'll take a look at those.

Did you ever see the 2N3055G & MJ2955 by ON?
Seems the same specs as the ST one as my first look. And cheaper that MJ15015/16G, for a reason that I don’t know.

 

[Joe_music]

So it was a ground problem.. had to verify every ground point on the power amp section and correct fews and was good after all.

BIAS/OFFSET adjusted at between 30.5 to 31.5mV and less than 1mV but plus that -1mv offset.

Only issue now is that im getta sounds at idle that come from the preamp section.

It follow the volume knob, balanace and the audio muting make it reasonably less audible and for now only way I could liste to music without have the "cchhh" sounds in background

 

[jock48]

So it was a ground problem.. had to verify every ground point on the power amp section and correct fews and was good after all.

Hi

So it was a ground problem.. had to verify every ground point on the power amp section and correct fews and was good after all.

BIAS/OFFSET adjusted at between 30.5 to 31.5mV and less than 1mV but plus that -1mv offset.

Only issue now is that im getta sounds at idle that come from the preamp section.

It follow the volume knob, balanace and the audio muting make it reasonably less audible and for now only way I could liste to music without have the "cchhh" sounds in background

Hi Jo_music,
I have the same version of this amp and have recently replaced a couple of transistors and most caps. Like a previous contributor I was trying to obtain the specific user manual for this version but still unable to access HiFi Engine. Just wondering if you still have it and if you would be kind enough to send a copy.
Many thanks, Andrew

 

[Joe_music]

Hi

Hi Jo_music,
I have the same version of this amp and have recently replaced a couple of transistors and most caps. Like a previous contributor I was trying to obtain the specific user manual for this version but still unable to access HiFi Engine. Just wondering if you still have it and if you would be kind enough to send a copy.
Many thanks, Andrew

Hi Jock48, my apologise for the really long response as I lost this account and moved from this NAD3020 until now to found my next project, a Sansui

Do you still need this manual? I currently still have my HiFi Engine account and can you out

 

[jock48]

Hi Joe, thanks for the reply. I finished that project but still have another of these amps to work on, so the manual would be really helpful if not too much hassle.
A Sansui sounds nice, I’m keeping my eyes peeled for one myself at the right price but so many models to choose from!
Thanks for your help.