9090DB, only tape 2 works

[Swan1493]

Avionic was right! My Dolby switch shaft had become disconnected. I must have dislodged it when reassembling after the initial pinning of the Dolby board because it rotated when I cleaned it first time through. The plastic ring that secures the shaft had cracked so it easily slid in and out.

I then traced an intermittent channel drop to a solder joint connecting the Dolby board to the Dolby volume switches. Just got a restored osciliscope off eBay and this was great project to start the learning process.