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-   -   NAD 1020 Preamp Problems (http://www.diyaudio.com/forums/solid-state/62671-nad-1020-preamp-problems.html)

gmilitano 17th August 2005 05:41 AM

NAD 1020 Preamp Problems
 
I am having problems with a NAD 1020 Preamp. The unit powers up fine and the 120V plugs in the back of the preamp also work as I can power a phono or CD.

The problem is that I get no output signal. If I turn up the volume all the way, you get some very distorted and scratchy thumps and pops that is generally coincident with the bass of the music being played.

I popped the unit open and there is nothing that looked obviously cooked.

Does anyone have any suggestions as to where the problem may be?

It does not seem to be a power supply problem. I fear that one of the transistors may be cooked in which case I doubt I would be able to track the bad one.

Any help would be appreciated.

maf_au 17th August 2005 05:58 AM

I'm only a newbie, but the first thing I'd do would be to check for dry solder joints.

Michael

gmilitano 17th August 2005 02:36 PM

I looked at the board and did not see any obvious signs of bad connections.

The tape monitor is working, so the problem is in the preamplifier section. The headphone also does not work.

Could this sort of problem be the result of a dried out electrolytic?

gmilitano 17th August 2005 10:59 PM

I was wondering if anyone has a schematic for the NAD 1020?

It just struck me as strange that both channels are out on what is a discrete stage transistor preamp. I am now thinking that the power supply may be the problem.

anatech 18th August 2005 02:21 AM

Hi GG,
Yup, power supply or muting circuit. Power supply could cause that as well.
Follow the signal with a 'scope (got to love those things).

-Chris

gmilitano 18th August 2005 04:50 AM

Quote:

Originally posted by anatech
Yup, power supply or muting circuit. Power supply could cause that as well.
Follow the signal with a 'scope (got to love those things).

-Chris


I measured 50VAC from the transformer and 63.5VDC after rectification. So there are no obvious problems with the power supply. I will have to look at it in more detail. Could bad powersupply caps be the problem?

I listened very carefully with headphones and there is a very very
weak (almost inaudible), but clean signal. However, when you turn the volume way up, the signal remains very weak, but you get the ocasional loud distorted thump and pop that is coincident with the loud parts of the music.

I have a two channel scope, but only one probe. I have some basic electronic skills, but I am still learning how to use the scope. Do you have any tips or suggestions on how I should go about tracking down this problem?

I am also starting to think it may be a muting circuit problem, but that does not explain the loud pops? Could a faulty ground or a short going to the ground also cause this problem.

planet10 18th August 2005 08:11 AM

Not the 1020 manual, but the 1020 is the preamp out of a 3020 so this may help

http://p10hifi.net/planet10/NAD_3020_ServiceManual.pdf

dave

Cobra2 18th August 2005 08:47 AM

mute?
 
I think it has a mute-relay, that keep outputs muted for some seconds after power-up.
Listen for a small click within 10 sec.
I have had other NAD preamps with faulty delay/ relay-driver-circuit.


Arne K

gmilitano 18th August 2005 01:37 PM

Re: mute?
 
Quote:

Originally posted by planet10
Not the 1020 manual, but the 1020 is the preamp out of a 3020 so this may help

http://homepage.mac.com/planet10/NAD...viceManual.pdf

dave


Quote:

Originally posted by Cobra2
I think it has a mute-relay, that keep outputs muted for some seconds after power-up.
Listen for a small click within 10 sec.
I have had other NAD preamps with faulty delay/ relay-driver-circuit.


Arne K


Dave, thanks for the manual.

Cobra2, there are no relays. You get sound as soon as you power up. The tone, bass and balance controls work on the very weak signal I am getting. If you turn up the bass, the distorted thumps and pops occur more frequently.

I'm not really sure where to look from here.

Leolabs 18th August 2005 03:48 PM

try to measure voltages around certain critical points:)


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