NAD 3020A No sound after changing capacitors.

[Station X]

Originally Posted by Nickaliath

When he hadn't used it for a while, It would take a while till the red light turned on. Which I presume is a cap issue powering up?

The red light, or LED to be more specific, is part of the -25.6V power supply circuit. A few simple checks with a voltmeter would soon have shown where the fault was.

[trobbins]

Originally Posted by Richardgr

A lot of headshaking over replacing 20 year old electrolytics. Possibly they were 5000 hour rated parts, well beyond their allotted lifespans.

A 5000 hr rating is typically a specification rating at max temp, max voltage, and max ripple, and compliance is typically for no more than a nominal reduction in capacitance value and dissipation factor (ie. conditions that still likely don't affect equipment operation). So 'well beyond allotted lifespan' is misnomer imho.

Nickaliath, I also couldn't find a directly associated schematic for my 3020 series 20. I did note at the time of servicing that C601, C603 schematic polarity was wrong.

As an aside, I also inserted 4R7 1W in base of each output semi 2N3055/2955 to minimise damage if output stage goes – somewhat common problem. And inserted 0.33Ω 3W in each emitter for thermal stability with any sort of 2N3055/2N2955. And inserted 1Ω 1% sense resistor in each 2N3055 collector path (bypassed with link). And inserted D605/606 in place of J35/36 links (older revision ?) and positioned diodes on heatsink to give 2 thermal junction biases. And changed trimpots for 10T (including RX1, RX2) as existing trimpots were poor. But these are more onerous mods, and imho amp is best cautiously checked using a variac, and with separate stage enegisation.

[electrogram]

I once bought a NAD amplifier at a car boot sale very cheaply. When I got it home I found it didn't work. On looking round the back I discovered the linking loops between pre- and power amps were fitted incorrectly, one joining L+R pre- amps together, the other joining L+R power amps together. Just a thought.

[Nickaliath]

Thanks for all the replies.

Luckily I have now found the correct capacitor list online, So have this if needed by anyone else in the future.
So first thing I will do is go through all that I fitted, To make sure I didn't make an error somewhere along the line. The few I checked last night, Were all ok.


I totally get what people are saying about changing capacitors for no reason. The person I know was asking if I could do it for him, So this is why it was done. I think he was mainly worried about potential leaking in the future, From what I gather.


I have checked the bridge for the pre-amp and they are fitted correctly.


The sound is very quiet on both left and right side.

[Sideband]

Don't know the amp at all but if there is a muting circuit possibly operated by relays, then it's worth a check. Seems unlikely for both channels to fail so look for something common to both.

I had a call once from someone who had 'changed all the caps'. It had very low output on both channels. There was a solder splash (difficult to see) across a BC848 surface mounted transistor controlling the mute circuit (common to both channels). A quick clean up of the solder and away it went.

Worth checking

[sortedradio]

Originally Posted by Sideband

Don't know the amp at all but if there is a muting circuit

I know that at least some, if not all, 3020 amps mute the speakers at power on for a short time. There is a capacitor that sets the time constant which I have had fail, causing the amp to remain in mute mode.

[Patrick Dixon]

Originally Posted by ben

Why stop there? Don't forget those 20 year old diodes, resistors, transistors, pots, wire, transformer...

However, those components generally don't have a history of ageing badly - unlike electrolytic caps!

[Silicon]

Don't forget that modern capacitors sometimes leave the factory in a faulty condition.

You can't test a capacitor thoroughly with a multimeter.

[Goldie99]

@Nickaliath - if the 3020 you're working on is the early version (with separate PS pcb), I still have the e-cap (+/-) orientation details here if you need them.

[Nickaliath]

So I have been through all the capacitors fitted and they are all the correct types / orientation.

They appear to all face negative the same way.

I will give it a check over for any solder bits left over, Hopefully I cleaned it enough as I went along.

Will also check the muting side, To see if I can find anything there.
That does sort of make sense, As there is low sound. Which does increase with volume control. But still very quiet.

I was worried about a potentially faulty new capacitor. I have a DE-5000 which tests capacitance.

It doesn't have separate board for the power.


The main thing I was starting to wonder, Is if I have dislodged something in the process of swapping capacitors.
So there's a dodgy joint somewhere.

[Station X]

Time to get your meter out!

[Edward Huggins]

Although I commented earlier a tad harshly, I'm sorry you've gotten yourself into this. Suggest you look under a 12x glass for dry-joints, solder blobs and possible cracks in the PCB where you might have encountered some resistance during the earlier change out. Hopefully you will relay your predicament to your Customer! Assume you have measured the main DC voltage rail.

[paulsherwin]

The first thing to do is check all the power rails and other voltage test points. A power fault is by far the commonest cause of symptoms across both channels.

You should be able to connect the preamp outputs to another amp to establish that it's producing the correct levels.

[Radio Wrangler]

With transistors, it's usual to have feedback around stages. Kill thecpower to a stage and with the active bits of the stage not working at all, you'll usually get a little bit of signal bypassing the stage via the feedback components. So big differences like the complete loss of power to some stage can leave you with very low output.

For this sort of testing a scope can be a lot faster and easier to understand than multimeter readings. Just probe along the signal paths and see where it vanishes. You also get to see DC conditions at the same time.

David

[Jez1234]

As both channels are off it would be worthwhile to check voltage rails to things like the pre amp and tone controls section (assuming it's not a vol control feeding into power amp type integrated.

[Nickaliath]

Thanks again for all the continued support.

So just in case there was dry joints or breaks, I went over the whole board to reflow. I just thought is was an easy place to start.

No difference unfortunately.

The annoying thing is, That I am just doing it as a favour for the person.

I did notice on the capacitor list that it shows C531 as a 47uf 63v, Whereas the one I replaced like for like is 1000uf 6.3v. I think this is the main capacitor for the muting circuit.

But then it was working before, So must be fine.

I will get the meter out tomorrow and start going through voltages.

[Goldie99]

Can you post a clear top view photo of the amp - there seems to be a lot of confusion as to exactly which variant you actually have ?

[andrewn]

Many years ago I bought a faulty NAD 3020 (I think a series 20) at a radio rally for less than £5. It had a very weak distorted sound. The fault was two caused by a pair of JFETs. I can't remember the part number, I think it might have been J111. I remember the replacements were inexpensive and the amp has been working fine ever since. My brother uses it as part of his hi-fi setup.

[Jez1234]

Hmm J111 is a switching FET and could well be used in the mute section...

[Goldie99]

Originally Posted by Nickaliath

I did notice on the capacitor list that it shows C531 as a 47uf 63v, Whereas the one I replaced like for like is 1000uf 6.3v. I think this is the main capacitor for the muting circuit.

C531 is indeed part of the muting circuit, in at least some 3020 variants, and is usually a 47uf / 63V cap, although in use it actually has 70 - 80V across it (I use a 47uf / 100V). If you've put a 6.3V rated cap in, I'd start checking there.

Alternatively, if there was already a 1000uf cap there, it's either been changed already by someone else, or I'm using a different 3020 circuit diagram.