RT-909 - pinch rollers engage when fast-forwarding/rewinding

[stragulus]

Hey folks,

As part of a restoration project I'm working on an RT-909. When I press fwd/rewind, the pinch rollers engage, and thus it pushes the tape up against the heads. Very undesirable obviously! Now I've already rebuilt the tension rollers using Rich's guide (thanks!!), and they perform like new. New switches included. Only other thing I've done so far to this machine is to replace the belt and the pinch rollers.

When the tape is threaded and no function is selected, I can disengage the pinch rollers by moving one of the tension rollers to the lock position. They'll immediately and consistently disengage. Move the tension roller back, the rollers stay disengaged. Pressing fwd OR rewind will first engage the rollers, then start moving the reels. What the..

This already was like this before I touched the tension rollers. What black magic is going on here?

 

[stragulus]

So I've been digging into this for a bit. Everything measures correctly, there's no voltage drop over the solenoid after pressing stop, the controlling IC also functions correctly. Yet, the pinch rollers stay up. When I turn the deck off, they drop though, hence me concluding that it must be logic. But, turns out it looks like the solenoid itself may be the culprit? If I turn on the machine and just press the pinch rollers up, they also will stick. With the machine turned off however, it doesn't stick and drops down pretty much instantly. How is this possible?

Edit: Seems to be related to the capstan spinning? Turning the deck off or moving the tension rollers to lock position both make the capstans stop spinning, then the pinch rollers drop

 

[stragulus]

I never updated this, did I? If someone happens to stumble upon this; the issue was the *pause* solenoid that was being kept engaged. The voltage was low enough for not to self-engage, but once activated it would not release anyymore. The fix was replacing an open germanium diode (D517), but there are many pathways to activate the pause mechanism so YMMV.