The NAD 7020 I brought home to fix the other day was calling to me, so I started on it yesterday and finished it today. I almost finished it real good, but the smoke seems to have cleared.
I have always liked NAD equipment. The brand does have it's detractors with stories of cheap parts and poor quality control. I don't have much against them, as I have always liked the performance for the dollar being the cheapo that I am while still wanting good sound. I don't even mind the look which others put down. I have had more devices from NAD than just about all other brands, and kept them for longer on average. I do admit I've also had to fix more of them...
I used to have the NAD 3020 which was the integrated amplifier section of the 7020 receiver model. With that in mind I really wanted to play with this one from Clint.
Cosmetically this is in very good shape and has just a few minor scratches. It needed a good cleaning though. The usual dusting inside and cleaning of the switches and controls with contact cleaner I did yesterday. After plugging it it though I found another annoying issue.
When turned on, even after another spray of contact cleaner in the switch area, the lights and also the sound to a degree sputtered and flickered. I've seen this before and decided to see if I could deal with it. It usually comes from electrical arcing in the switch and I saw it most seriously in a Pioneer SA-450 receiver, and I still have not fully addressed it there. The culprit in the Pioneer and as it turned out in the NAD was an ALPS brand switch.
It's a different model this time and appeared to be easier to access so I decided to go for it.
Disassembly had to come after removing around 20 screws to get the cabinet and face plate out of the way, plus a number of wires to de-solder. The parts inside the switch of course decided to sproing out before I got a good look at how they went together. Figuring out how they went back together was trail and error...and trial and error...and so on, for about an hour until I had it right.
Anyway, age, dirt corrosion and so on lead to the arcing which blackens the switch contacts with soot or something similar. Taking things apart and scraping & sanding is just about the only way to address it. A simple spray cleaner does not do the job when it gets like this.
When I first saw it the round pad on the lower piece was as black or worse than the part above it that it had to make electrical contact with in order to turn on the receiver. There is another set inside the switch as well. Scraping with a screwdriver blade and sanding with emery paper cleaned things up quite well. This was the easy part. Now I had to put it back together.
Eventually I managed to figure it all out, had it reassembled and soldered together and had no flickering when I powered it on. So I reassembled the case, with the 20 screws of different lengths.
That's when the next problem arose. I had tested it before and the receiver had worked with headphones, tuning in AM & FM radio stations. Connecting a turntable and speakers came next... and so did the smoke!
It made sound, but a little curl came up from the cabinet in the tuner area. Powering it off and examining it, it looked like the smoke had come from a point on the main circuit board near one of the screws on the bottom panel. I am pretty sure I simply used a longer screw in that hole than it should have had and it must have contacted the foil side of the printed circuit board.
I moved some screws around, making sure the shortest ones were in those areas. I am only talking about a difference of 3 or 4 mm at most, but it was critical.
Anyway, no more smoke and it works great! No sparking, flickering, or scratchy sounds...just music!