Saturday, 31 October 2020

NAD L70 receiver refresh

On the bench today is a NAD L70 receiver. It's a bit newer than the stuff I generally like to work on with NAD, but it was going really cheap, and is cosmetically pristine, so I thought I'd have a play.

There were two symptoms of bad behaviour. Firstly, a truly dreadful hum present in both channels, and secondly the CD/DVD player was really flaky, reporting "no disc" as often as not, and pausing and stuttering quite a lot while playing when I could get it to recognise a disc.

On opening it up it was really obvious what was causing the hum. There are 4 large capacitors on the top (CPU) board, that provide smoothing for all the lower voltage DC supplies. A couple of these were obviously bulging. So I whipped all four out and replaced them with 2200µf 25V 105˚ Panasonic electrolytics. While I was there I replaced a bunch of the smaller caps nearby.

That sorted the hum. Next up was the misbehaving CD/DVD player.

This is a real bear to get to, being underneath the CPU board. In order to get the transport out you have to first open the tray and unclip the oval NAD bit on the front. Then retract the tray again, open the cover, remove the CPU board, and it's pretty obvious.

The transport is an ATAPI/IDE one, made by Raymedia (RMC) part number RL-A700. This is common to a lot of CD, DVD, and SACD players of the period.

Once the transport was out, I started by popping the top cover off and giving the lens a wipe with a kimwipe and a little isopropyl. I cleaned the dried grease off the sled slides and gears, and relubed with Electrolube Special Plastics Grease (SPG), which is just for this.

Cleaning didn't help. The supplies were tested good, and this transport really has nothing to adjust, so I next ordered a replacement pickup. Part number for the pickup is SF-HD60.

It arrived after a couple of months, and I fitted it today, removing the anti-static solder blob after fitting.

This made a really big improvement, but it still stalls very occasionally and 2 or 3% of the discs I've tried today don't read. After repeating the clean, relube, reassemble, test cycle a couple of times, including pulling the spindle motor and giving that a bit of a spray of iso (did I mention that it's a pain to get to the transport under the CPU board), I've decided to bite the bullet and just order a whole new transport for it.

So that's where this one is at. It actually sounds really good, and with the exception of three useless channels will make a lovely all-in-one stereo. I think I'll set it up in my office at work once it's finished.

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