TMCC Cab1 red knob spins freely - won't hold its speed setting

Here's what I do periodically to renew the Cab-1 red knob.

1) Remove the 6 screws from the back of the Cab-1.  Note that the two screws at the bottom (by the red knob) are shorter than the other 4.

2) Separate the halves of the Cab-1 by gently pulling them apart.  There are some wires near the top that will keep the halves from completely separating, but that is okay.

3) The metal knob shaft fits into a hole in the rear half of the Cab-1 housing.  Stick a small (1/4 x 1/4 inch or a little larger) piece of masking tape over the hole.

4) Put the Cab-1 halves back together.  Be sure that the optical sensor board next to the red knob shaft fits into the plastic slots that hold it.  You'll need to squeeze the Cab-1 slightly so the knob shaft can pierce the tape.  A flap of tape will get pushed into the side of the hole effectively making it smaller and creating some friction for the shaft.

5) Replace the 6 screws, making sure that the short ones go in the bottom of the case.

6) If the knob still rotates too freely, open up the unit and add a second piece of tape on top of the first.

This fix has worked for me many times.

Thanks Bob for the tip.  I was hoping there might be an adjustment to make, but I guess otherwise the masking tape technique at least makes up for some wear and tear which I suppose is the root cause of the free spinning.  A friend of mine's Cab-1 knob turns with at least some resistance and holds its position.  I bought the TMCC set in 2005 when the first AF TMCC engines were releases and used it until Legacy as announced.  Then for years the TMCC was put away.  Guess I may have used it more than I remember of realized.  

I've had TMCC knobs that had alot of resistance, others were very loose out of the package. No rhyme or reason, but its a good thing Lionel added detents to the knob rotation of the Legacy handheld.

 When it gets really interesting is when the rheostat of the knob fails completely and trains take off at full speed. If your lucky..... after a few rotations of the knob, "zero" will reappear. I've had bad ones out of the package as well.

Thanks Ricko.  I haven't had a rheo blow, but can imagine how much of a surprise that would be.  I recall now also some inexplainable differences between Cab-1's knob resistances when that was what we were predominantly using (pre Cab-2) and that was prior to much use on many of them.  I'll open mine up and see what I can do.  

I opened my Cab-1 last night.  I inserted a short segment of Q-tip shaft in the hollow post molded into the back half of the Cab-1 shell that sits atop the end of the shaft of the red knob when reassembled.  I then clipped the Q-tip shaft just a hair longer than flush with the end of that hollow post using end-nippers and reassembled the Cab-1halves.  The clipped end of the Q-tip contacts and applies gentle pressure to the end of the red knob metal shaft.  My red knob now turns with a comfortable degree of resistance and the remote actually works more responsively than before - only a partial turn generates a change in engine throttle and speed.  No more untimely or unwanted free spinning or lots of movement of the knob to change speed.  Bob, thanks again for the masking tape tip.  I see how that would achieve the same result (create drag on the end of the red knob's shaft), but thought I'd try this Q-tip stub approach and see how it works.  I'll let you know how it holds up.   

Dave

UPDATE:  The Q-tip extending just beyond the end of the hollow post created a nice degree of knob-spin resistance, but apparently created some stress on or distortion of the knob's shaft and or optic throttle sensors that flank it causing the Cab-1 to not always work as it should.  For example, turning the red knob counter-clockwise could occasionally result in the engine speeding up instead of slowing down.  However, cutting the Q-tip shaft flush with the end of the hollow post restored proper red-knob throttle response and leaves the knob with a reasonable amount of spin resistance or sense of control - much better at least than the free-wheeling/free-spinning that it had before.   

Dave