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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment.

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Old 30th Jun 2020, 6:56 am   #1
Big jim
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Default NAD 302 Repair

The problem with this amplifier was no sound. Both channels had -3.4V DC on the o/p I found that the +38V was missing, I then found that R513 1k5 o/c and C518 s/c. This model is easy to work on and gives excellent result.s I hope this of help to all.

Jim.
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Old 3rd Jul 2020, 4:14 pm   #2
John_BS
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Default Re: NAD 302 Repair

Thanks for posting: it's always useful to have the results of fault-finding recorded. Many people forget to return to say what worked/didn't. The forum is keyword searchable which makes these posts invaluable.

John
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Old 4th Jul 2020, 1:20 am   #3
trobbins
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Default Re: NAD 302 Repair

I've recently repaired a 3020, 3240PE and its optioned up 7240PE, and a Proton A300. Many of the electrolytics in the earlier NADs were either high on ESR or low on capacitance, so that can often lead to a blanket replacement although replacing the 'big' caps can depend on whether the amp has had a lot of use and how those expensive caps measure for value, ESR and leakage.

The other concern with that era of NAD was the lack of any output stage emitter resistors, and in the earlier amps a lack of base resistors, which can lead to output stage faults that take out a few parts, and a susceptibility of bias to thermal changes. Luckily the pcbs typically allow emitter resistors to be added.

And have a contact cleaner/lubricant spray can ready for noisy pos and switches.

And the earlier models used a low-grade rear panel slide switch for 4 to 8 ohm speaker impedance selection, which switched between power transformer secondary high current taps. Best to disable that switch and solder the selection of impedance, before someone slides the switch during operation and takes out the power supply from poor contacts.
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