After repairing a DDIII with the magic gear another issue emerged. The transport now seems to be flawless but the sound has a "fall" every half a second or so. Don't know if the issue was present before: because of the cracked gear it sounded errant so maybe the issue was there among the others. I don't know how to describe it better, so I'll post a recording made with the 3000 Hz cassette so that is distinguishable. Any idea on what could it be? The mechanical speed seems to be constant, maybe it's a capacitor's issue?
Sounds like a Gear is cracked, check all gears, sometimes the cracks are very small and the Gear is not tight with the shaft. On the DD it’s often the Gear for the Reel. http://walkman-archive.com/articles/sony-dd-repair-guide_06.html and have a look on the Capstan Rubber and Rubber Ring
Thank you Harry. I'm very aware of that tutorial, I never could open a DD without it In fact I did replace the rubber capstan tire, so that shouldn't be the issue. Regarding the cracked gear i don't know... I'll have to open it again. I am doubtful about the gear because shouldn't the speed be dictated by the capstan and not the reel?
A cracked Gear can give „feedback“ to the Capstan. Have you checked the Capstan Roller itself? Or the rubber where the Motor is pressed on? Is the Motor running silent? Even the bearing of the Motor can need some Oil...
To me it sounds like its coming from the capstan roller (rubber ring). The diameter of this ring ist approx, 8mm. Periphery of the roller is d x pi = 8 x 3.14 = 25.12 mm. The tape speed is 47.62 mm/s. If you divide the tape speed with the periphery of the capstan roller you get roughly the "rhythm" of the sound sample.
In fact analyzing the roller it has a flat spot, well spotted guys! I'll have a replacement roller and I'll try to mount it. It scares me a bit to dismantle the head support, it's the first time I attempt to do it...
