Revox PR 99 tape snapped when press play

[almandog]

PR 99 MKII:
Background on the deck:
The deck has been totally recapped. The heads are brand new and they were sent to JRF magnetics to be mounted on the headblock. So no issues expected with the heads. The metal Brake bands were also changed with new ones. New motor bearings and pinch roller also. The electronics is working, and the deck play and records.

But before I go any further with any adjustments, I need to sort out the tape transport:

When I press play the tape "Snapped" at the pinch roller with a "wobbly" sound.
I matted the capstan shaft with sandpaper on the old pinch roller, cleaned the tension arm, observed the tape path while the tape was running to see if the tape touches the tape guide on the left side and the right side. Tape not touching. See the link below for further details on this issue.

https://drive.google.com/file/d/19lV...w?usp=drivesdk

I also tried to adjust the brake torque per the manual. The measurements from the String test around the reel don't measure up at all with the numbers on the diagram in the manual. See picture below: my measurements are circled. I have tried all the settings on the brake bands but don't see much difference.

 

[Dave3009]

I don't have a PR99, but that seems to be a lot of tape bounce compared to my A77. It looks like the tape is very loose after it stops and then the slack is bouncing around when it goes into play. Those very low brake forces look suspicious. I assume the PR99 has a cue mode that puts the tape in contact with the heads and guides but does not quite engage the capstan. Try going into cue, tension the tape by hand with the reels, then hit play. Does it still bounce? Could be the supply reel brake is not braking enough to keep tension as the tape stops, or the time of the transport is off.

Dave

 

[almandog]

Dave:
The PR99 does not have a cue button. It only have a tape dump button for editing the tapes.

Mando..

 

[Dave3009]

Well anyway, after a stop from play is the tape loose or is there slight tension. From your video it looks like after a stop the tape is not in tension. That would indicate to me that your supply reel hub is not braking properly.

Dave

 

[almandog]

I did adjust the brakes again and now when the tape stops the tape is straight without any sagging like before. But on play the snapp is still there. I guess I might have to leave well enough alone because everything else with the transport is all good.

 

[Dave3009]

One more question. Did the startup snap behavior exist before you sanded the capstan? My understanding is that Revox specifies a polished capstan. I know my A77 and every other Revox I have seen have polished SS capstans, while my Otari's use a matte capstan. It's reasonable to believe that the capstan surface could affect the initial startup of the tape. The rough capstan would have higher initial static friction at the moment the pinch roller engaged, accelerating the tape slightly faster than a polished capstan. That might upset the brake release and take up reel startup timing. As you say, not much you can do about that now. As long as the snap is not breaking or stretch tape and you compensate for initial speed instability and lack of head contact, its probably not worth worrying about. BTW that's what cue mode is for - I surprised the PR99 left that out.

Dave

 

[almandog]

Dave:
I dont recall what happened before I matted the capstan shaft. On another forum people were recommending the matting and since I was rebuilding the deck I went ahead with the matting. But your explanation sounds reasonable about the smooth capstan shaft.

Thanks a lot for your comments.

Mando..