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NAD 712 repair

NAD 712 repair and restoration

This is a NAD 712 receiver that came in for repair and restoration. Our customer stated that it simply wasn’t working; it would power on, but there was no audio output.

Additionally, this was going to be a gift, so our customer wanted it cleaned up as much as possible since it had some dust and debris inside. The 712 was released in 1995, so it’s been around for nearly three decades.

The first step was to figure out why we had no audio output. After some investigation, it appeared like the amplifier section was intact, so that was a relief. It wasn’t being powered on, though, and we determined that was because of a missing +5V signal that was required for the relay to energize.

The +5V supply was present, but was being pulled low to just over +2V. The layout of the NAD made this easy to troubleshoot. We simply isolated sections that ran on the +5V supply until we zeroed in on the culprit.

The LM7000 IC above is a PLL (phase lock loop) frequency synthesizer, and it’s part of the AM/FM tuner section. There was an internal fault causing the issue on the +5V supply. This is a long out-of-production IC, but thankfully we were able to locate a replacement.

After removal and replacement, we saw that the fault was gone and we had a good +5V supply! Once we determined it was safe to do so, we powered on the entire unit, and the relay clicked on as expected. It’s always exciting to bring something back to life, and it was great to hear that the audio output now worked beautifully. The tuner, however, still wasn’t operational. Our customer declined for us to investigate further, as it simply wasn’t worth it to pursue.

With the audio issue fixed, we cleaned the board using isopropyl alcohol and some elbow grease. Move the slider to see the difference:

It now looks as good as it sounds, and we hope it has at least another three decades of use going forward. Big thanks to our customer for providing this little gem for us to work on!

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