NAD 302 Light on but no sound

[mark248]

Hello to All and thank you in advance for helping. I have a NAD 302 bought second hand in the early 2000's. I replaced it several years ago and it sat idle until a year ago when I tried to use it for a second system. When i turned it on there was an "electrical burning smell" I turned it off and thought I will repair it another time. Last week my Son was gifted a turntable so I thought I would see if I could get it going for him. I opened it up and the fuses are all burned out, the board seems to say 2x1a and 2x4a fuses. I have some 2a which i bought for my old Sugden A25 so I tried 4 of those. The amp now powers up with the green light on no electrical smell. I left it on for an hour to make sure there was no burning smell then wired up some old Castle Clyde speakers which i also want to give to my son. There is no sound, I have tried the CD, Tuner, tape and Video inputs, no sound. If there was sound I would have bought new fuses of 1a and 4a but now think a major component may be damaged. Any advise would be really appreciated.

[mark248]

Sorry, I forgot to mention that the switch that goes from 4 to 8 ohms has come out of its slot, it is set to the 8 ohm setting.

[Station X]

Hello and welcome to the forums.

What's your skill level and what test equipment do you possess? At the very least a Digital Multi Meter (DMM) will be required to check power supply voltages.

The circuit/schematic can be downloaded free of charge if you search online for it.

[barretter]

Are the two links from pre-out to main-in in place. Just a thought.

[mark248]

Thank you for the replies. I would say my skill level is about 1 out of ten, i have never soldered and have no testing equipment.....the two links are in place....

[FIXITNOW]

First port off call would be to check if the -/ +38v power rails are working you will need a test meter.

[mark248]

Thanks for the reply, before I buy a tester please can anyone give me an educated guess at what it might be and likelyhood, cost of getting it repaired?

[Station X]

Sorry, but I cannot answer your question. The fact all four fuses blew sounds serious and I'm surprised the replacements survived.

If I had the amp in front of me I'd reach for my DMM.

[paulsherwin]

Sadly, if you have no electronics skills at all the chances of you fixing this amp are very small. You would be better off finding a commercial repairer, though that may cost more than the amp is worth. You can buy decent amps from that era for £50 or less.

[mark248]

Hi Paul, thanks can you advise where i can find one for £50, on Ebay the NAD 302 goes for about £175...

[Mooly]

Given the burning smell I would initially suspect that the output stage of at least one channel has failed.

The output stages of these used no emitter resistors which meant they were extremely prone to thermal runaway. I believe there is a modification to add them in an attempt to improve reliability.

A satisfactory repair is a lot more involved than replacing just one part, you are probably looking at replacement output transistors, replacement driver transistors plus any collateral damage and also modifying the output stage to prevent such failure again.

[paulsherwin]

I didn't say you could buy a NAD302 for £50. They suffer from the 'NAD 3020' effect, so many people are convinced they're worth a fortune, and sometimes they do achieve surprising prices. You could certainly buy something with similar performance from Marantz or Cambridge Audio though.

[SeanStevens]

Hi,

NAD do make a nice amp and it might be a simple fix. But without any tools for the job . . . tricky

Is there anybody on this forum in the vicinity? They may be able to help.

Other than that it is time to buy a DMM for 7 euros and measure some voltages!

SEAN

[barretter]

Presumably you have another amplifier so you could try connecting the pre-amp out from the NAD into a line input (NOT phono) on the amplifer you use and carefully slightly turn the volume up to see if there is any output from the NAD. If there is you might just be able to change the power transistors on the NAD (if they are still available, that is a big IF). If there is no output the most cost effective solution, given the price of decent test and soldering equipment, would be, as people have suggested, just to buy another integrated amp.
From your description of the failure it sounds like there has been a massive short circuit so you would need to find that first.

[paulsherwin]

If several fuses have blown, that suggests output transistor failure in one of the channels - it takes a lot of fault current to blow 2A and 4A fuses. This is a classic DC coupled power amp failure mode and can be difficult to fix even for an experienced service engineer, as multiple components have probably failed.

[ajgriff]

I think I'm right in saying that the pre-amp and power amp in the 302 are supplied by two separate transformer secondary windings so it seems unlikely that a fault would have resulted in all four low tension fuses blowing. I'm wondering whether or not all the fuses did actually blow especially as the OP doesn't seem to have an obvious means of testing their continuity? Also it would be worth undertaking a careful inspection of the power supply components for signs of damage especially in the light of the burning smell when powering up after a long period of idleness. As an aside substituting 1A fuses with 2A alternatives is not a practice to be recommended in view of the risk of causing further damage.

Alan

[qualityten]

Originally Posted by mark248

Hi Paul, thanks can you advise where i can find one for £50, on Ebay the NAD 302 goes for about £175...

A quick look at completed listings on eBay, shows three NAD amps (two 3020es and one 320BEE) sold for under £60 on 3 August, with more sold for less than £100.

With no electronics skills, I would recommend looking at buying a replacement for your son. Although 3020 and 3120 are legendary budget amps, many NAD integrated amps, and those of other brands, are worth trying. I'd recommend looking out for a Rotel or Trio/Kenwood locally.

Failing that, if you put a wanted request on this forum, someone might have something suitable for sale.

[dave walsh]

This is very clear and helpful advice Mark but some of the more technical stuff you won't have a hope of grasping. Overall though, it boils down to an assessment that your amp has probably suffered a catastrophic event with a silent cascade/chain reaction that has taken out a great deal more-perhaps equivalent to a car losing all it's oil at high speed. You would need a garage, a new car or both. People often assume things are a simple fix and have done for decades. This may [sometimes] be the case but not in yours, unfortunately. It would take quite a long time to reach the knowledge base to fix this 302 [I haven't got it] but then it would probably not be worth it on every level. If you wanted to get into the restoration hobby, then you would be very welcome and there would be lots of support available but that doesn't seem to be your aim. Hope that helps.

Dave W

[mark248]

Thank you for all the replies and advice, much appriciated.