This was another one of my recent summer acquisitions. Weighing in at just over 45 lbs and almost two feet wide, the JR-S501 was the top of the line receiver that JVC had to offer in the late 1970s and early 1980s. It is the big brother to the JR-S401 and JR-S301 models released at the same time. Rated at an incredible 120 watts per channel RMS, this thing is a monster. With an extremely low THD rating of 0.008% and a 95dB SN ratio, it is also one of the cleanest sounding receivers you'll hear from that era.
Another standout feature is the five band SEA (Sound Effect Amplifier) graphic equalizer, which not only provides more control of the sound, but also introduces far less distortion than standard tone knobs found on most other receivers. JVC actually licensed this technology out to various other high end manufacturers, one of which being McIntosh who apparently still uses it today for their modern equipment.
Unlike some of my other recent restoration projects, this unit needed a bit more work. The main issue was that the power switch only worked half of the time, and when it did, the lights cut in and out repeatedly. After removing the top cover, I immediately saw the problem. With the power turned on, I could see electricity arcing within the power switch assembly—a healthy wisp of smoke followed as well.
My first attempt to fix it involved desoldering the switch from the circuit board (got some good practice doing this) and taking the switch apart. Inside I found that the metal contacts had been almost fully corroded from constant arcing. I tried to clean them up with some contact cleaner, but it was futile. The switch needed to be replaced.
Finding a replacement switch for a vintage receiver that perfectly matches the circuit board is just about impossible. I tracked down the part number from the service manual, and a few online parts stores claimed to sell it, but they all listed it as "out of stock". I contacted a few of them to get specific information regarding it's availability, but nobody responded.
Out of options, I contacted my cousin who helped me with the Sansui AU-5900 a few months back to see if he had any suggestions. He suggested we buy a modern switch that closely matched the dimensions of the original and build our own damn circuit board for it. It sounded crazy, but he was confident. The power switch had its own little circuit board that was separate from the rest of the receiver, so I knew it wouldn't be too difficult. We took measurements, ordered the parts, and waited.
A few days later, I took the receiver to my cousin's place where he showed me his work. He actually integrated a TRIAC into the circuit which greatly reduced the voltage on the switch, essentially guaranteeing that the arcing problem will never happen again in the future. This was a suggestion I had previously read about on Audiokarma.org, but I dismissed it as an option because I had literally no idea how to do it myself.
With the switch replaced and the new circuit board wired and mounted into the receiver, it was time to reassemble everything. Accessing the power switch was pretty tricky, and I had to remove the tuning string for the radio to get to it. Even with the re-stringing diagram in the service manual, it was a huge pain in the ass to get right. I think it took us more time to re-string the tuner dial than it did to replace the power switch. Finally though, we got it, and the receiver was back in one piece.
I've been using this receiver as my primary unit for the past few weeks, and the new power switch works gloriously. It's just a shame I can't utilize all 240 watts while living in a condo.