Take-up reel motor: poor fast forward

10-1/2" reels / ¼" machine.

My unit started to suffer from poor FF function – and in an odd way. Works excellent when all the tape is on the supply side, fast forward is selected, and you allow all the tape to run to the end. Still works excellent when about one-half the tape is allowed to FF, stopped, restarted in FF, and run to the end. But if you run around three-quarters or more of the tape, stop and restart FF, the reels just sit there; stalled. BTW; rewind function still perfect no matter how much tape is on either reel.

Brief Functional Description: The motor is simply an AC motor with a run capacitor. The three reel torques needed in operation (Play-Small Reel Size = low-low torque / Play-Large Reel Size = medium low torque / FF = high torque) are controlled using wire-wound resistors to vary the voltages to the motor. All this switching is provided by both the transport logic (via a relay) and the front panel reel-size switch.

Actions: Went ahead and put in a nice new motor run cap which I bumped up to 6 µF as the 5.5 µF OEM value was too hard to source. No change. Started a big, fancy chart and started to record motor voltages in various conditions. Was wondering if the supply motor was somehow "fighting" the take-up motor when lightly loaded with tape as that motor's torque is also controlled and varied by the transport logic.

Solution: During all this testing I started to notice the guide roller (the one left of the heads) was squeaking now and then. This roller is supported by two very nice quality NSK ball bearings and turns absolutely freely and without issues of any sort when spun by hand. So, what the heck is squeaking?

It was the tape itself!

Now is it possible that this roller / tape interaction could cause my FF issues? Believe it or not – YES. All this time I was having trouble and testing I was using my "beater" tape. I did not want to mess up my good ones. As soon as I changed tapes not only did the FF issue go away, the guide roller squeaking also stopped. I have no idea the physics involved in the interaction of the amount of tape "wrap", the approach angle of the tape, or the back / front loading pull on this guide roller, but there must be something magic going on to create the perfect storm to create so much drag the take-up motor gives up only when most of the tape is on its side.

Motor cap PCB, pre-retrofit (1)

Motor cap PCB, pre-retrofit (2)

Old 5.5 µF motor capacitor (1)

Old 5.5 µF motor capacitor (2)

Motor cap PCB, post-retrofit (1)

Motor cap PCB, post-retrofit (2)

Reel motor (IB-963RA5) beside the voltage-tap board

Sony Devil Tape