NAD3020, no c422&c423?!

[xergo]

Hello all, just joined.
I have bought one NAD 3020 amp recently, and figured out that the phono preamp doesn't work. So I opened it up and noticed that the preamp has been short circuited (from c401/c402 to r427/r428). There are also some components missing in this circuit.

I decide to fill it with some components in the 3020 parts list. However, I have noticed, that there is no position on the pcb for c422/c423 (according to the 3020 pcb parts location/wiring diagram, the cap. should be directly near the r427/r428. S. attached image).

My question would be,
1.is this normal?
2.what kind of 3020 is without these two caps. originally?
3.are these two caps are absolutely necessary?

Appreciate any tips. Thanks!

An externally hosted image should be here but it was not working when we last tested it.

 

[Mooly]

Welcome to the forums xergo

I have no real answers on your NAD other than to suggest that you may be seeing different versions that appeared during its lifetime. It all looks very "original" from your picture.

If the phono stage isn't working then you need to do basic DC voltage checks around the transistors. Its highly unlikely both channels would be faulty. Check for common things like supplies and continuity of signal from input sockets to the board and continuity of switches etc. Some amps have links on the rear panel to link pre out to pre in ?

 

[xergo]

If the phono stage isn't working then you need to do basic DC voltage checks around the transistors. Its highly unlikely both channels would be faulty. Check for common things like supplies and continuity of signal from input sockets to the board and continuity of switches etc. Some amps have links on the rear panel to link pre out to pre in ?

Thanks Mooly. The whole phono stage is actually shorted through the two white wires in the attached picture. That is also why both channel don't work. I don't know why the former owner did that, maybe he or she had not found the suitable components.
http://s7.directupload.net/images/140128/97h3cpt9.jpg
Anyway, I am going to solder those missing parts in circuit. Just wondering if the missing C422/C423 on end of this stage will bring some negative effects...

 

[Mooly]

Any caps on the "end" of the stage will be for AC coupling (I think its a single rail stage... yes ?) So yes, you must include them.

(Without either having the unit in front of me or having an exact circuit its impossible to give specific advice).

 

[xergo]

Any caps on the "end" of the stage will be for AC coupling (I think its a single rail stage... yes ?) So yes, you must include them.

Thanks Mooly, that is also what I think.

I have attached the circuit of the whole pre stage from service manual.

An externally hosted image should be here but it was not working when we last tested it.

I am just wondering, if the caps are absolutely necessary, how could their positions be missing on the PCB (s. the first image I have attached in this thread). According to the 3020 PCB parts location/wiring diagram, the caps should be directly near the r427/r428.

An externally hosted image should be here but it was not working when we last tested it.

I think it is odd, because every component and their location on the PCB are identical to the service manual, besides these two caps.

 

[Mooly]

Pictures are to small to see

If you mean the cap locations are missing (no marking and no holes for them on the PCB) then you must be working to an incorrect circuit, perhaps one applicable to a different version of the 3020.

 

[xergo]

Pictures are to small to see

If you mean the cap locations are missing (no marking and no holes for them on the PCB) then you must be working to an incorrect circuit, perhaps one applicable to a different version of the 3020.

Oh, pardon! Here the bigger pix.
http://s14.directupload.net/images/140128/rblessqz.jpg
http://s14.directupload.net/images/140128/h8lhykq3.jpg

I have mentioned that besides these two caps, the other components and there locations (also marking and holes) on the PCB are just identical to the service manual. So I can not figure out, which version of NAD3020 do I have here. That drives me crazy... Any idea?

 

[Mooly]

C422 and C423 form an RF filter of around 330khz (470 ohm + 1nf). It will work without the caps but might be more susceptible to RF interference.

Maybe the previous owner linked the phono stage out to gain another line input.

All you can do is build it up to what you have and what you can see.

 

[TonyCH]

Xergo,

How to tell various 3020's apart, I think:
1. the data plate on back of 3020 and 3020A do not say which model it is.
2. the face of 3020 says NAD series 20 and Stereo Amplifier 3020
3. the face of 3020A says Stereo Amplifier 3020A
4. the data plate and the front face of 3020B, 3020e and 3020i do say which model it is.
5. RCA-connectors of 3020, 3020A, 3020B are pointing up.
6. RCA-connectors of 3020e and 3020i are pointing back.
7. 3020e has spring clips and 3020i has binding posts
8. 3020, 3020A and 3020B have the same button configuration on front, 3020e and 3020i have different front face

Hope this helps.

Please post general photos of this machine and the pcb from further out.

 

[xergo]

Xergo,

How to tell various 3020's apart, I think:
1. the data plate on back of 3020 and 3020A do not say which model it is.
2. the face of 3020 says NAD series 20 and Stereo Amplifier 3020
3. the face of 3020A says Stereo Amplifier 3020A
4. the data plate and the front face of 3020B, 3020e and 3020i do say which model it is.
5. RCA-connectors of 3020, 3020A, 3020B are pointing up.
6. RCA-connectors of 3020e and 3020i are pointing back.
7. 3020e has spring clips and 3020i has binding posts
8. 3020, 3020A and 3020B have the same button configuration on front, 3020e and 3020i have different front face

Hope this helps.

Please post general photos of this machine and the pcb from further out.

Thanks TonyCH, I think my amp meets point 1,2,5. So it should be the 3020.

 

[TonyCH]

Thanks TonyCH, I think my amp meets point 1,2,5. So it should be the 3020.

Well, then you have the original version.

Find the correct service manual which matches you machine and if you can't find one then you need good photos of other original 3020 PCB's.

I don't know about NAD service manuals or schematics but its not that rare that the manuals are wrong compared to actual production unit. Also its quite common that there is empty places for parts on working amp PCB's. And finally there might be some variation during productions runs which is not at all visible on all service manuals. Or several service manuals per model, usually the serials are mentioned. So, its best if you can compare with actual working unit of same model or at least to good pictures of it.

I do recaps etc. by looking at actual parts rather than the manuals or parts lists. This is obviously impossible if parts are completely missing.

 

[xergo]

The photos:
http://s14.directupload.net/images/140128/erroz3ps.jpg
http://s1.directupload.net/images/140128/a28wlra7.jpg
I think, this amp should be the original 3020 and that is why I use the service manual of 3020 in the first place. Only those two caps...

 

[xergo]

I use the service manual provided by planet10 in this thread:http://www.diyaudio.com/forums/solid-state/141705-nad3020-mystery-me.html
I have also browsed some good photos of original 3020 PCB and there are really those two caps on it. This makes me really confused.

 

[TonyCH]

It seems that there is more than one service manual for the first series of 3020. So, there was some changes during production.

I have 2 different ones and one has the same general component configuration that your unit seems to have. Don't know if these 2 manuals cover the whole series or just part of it. You might have them already.

 

[TonyCH]

Look at these, yours is the top one:

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

They look very much alike. Where are the caps you wonder about?

EDIT: ok, sorry. Didn't see your last post until now. My early model manual is the same as you have in your link.

 

[xergo]

Actually, I only have one service manual which planet10 has in other thread provided. (s. http://www.diyaudio.com/forums/solid-state/141705-nad3020-mystery-me.html)
Could you please advise a url where I can download the other version of service manual you have? Thanks!

 

[TonyCH]

I just looked at your first post image and read your problem with a thought.

Look at the two images above. You have no missing caps in that area. Your caps are excatly like the service manual photo.

You have 2 extra wires at that area though.

 

[xergo]

Hi TonyCH, please see the attached pix.
http://s14.directupload.net/images/140128/8uycmii8.jpg
http://s7.directupload.net/images/140128/kz9xa4bh.jpg
The location is marked with yellow circle.

 

[xergo]

I just looked at your first post image and read your problem with a thought.

Look at the two images above. You have no missing caps in that area. Your caps are excatly like the service manual photo.

You have 2 extra wires at that area though.

Yes, those 2 extra wires linked the input and output of phono stage, which is done by the previous owner of this amp.

I am just not sure if there are those two caps in the photo in the service manual. However there are clearly the C422 and C423 in the location diagram and schematic.

 

[TonyCH]

Yeah, the service manual photo shows 3 resistors (R425, R427, R428) where you have none but instead those you have some extra wires (did you mention a short between them?). I cannot see extra caps in that area in the manual photo.

On the manual photo there is a weird shadow near the c423 (does not look like any cap on the board) but there is absolutely nothing where c422 is marked.

Take the bottom off your amp and see if there has ever been anything soldered to those unmarked places on your amp. Note that those 2 are marked different on the manual to all other caps on the amp - that might mean something (?).