Odyssey Run Away...Again

Look closely at the magnet ring, I had one with a hairline crack and it took off.  Of course, it could also be the sensor, wiring, or the DCDR-S board.

I am no TMCC expert, but during diagnosis of a recent problem with a Mountain, I was advised that you can check the speed sensor for correct operation as follows.

With track power on, use a DVM to check for +5 VDC between the two outside pins of the 3 pin speed sensor plug at the DCDR-S board, as you rotate the flywheel by hand. The voltage should cycle from zero to +5 VDC and back again as the flywheel rotates. If so the magnet and switch are working correctly.

Rod

Rod, That would make sense. It would indicate that the hall effect device is turning on and off. 

Pete

Just a followup on the above engine. I tried the test Rod suggested and got ones but no zeros (5v high). I ordered and received some fix it magnets and a sensor board. The owner is on a budget and was reluctant to go for a Cruise M. After fabricating a flywheel puller I removed it and installed the fix it magnet. No joy. Then I swapped out the sensor board and it worked......sort of. It looks like someone tried to repair this engine in the past. The magnet ring had a lot of excess glue around the edges as if someone replaced the magnet ring, not using a fix it magnet. With the shell off I noticed with engine moving forward it worked as expected but when reversed the worm gear would move the motor shaft away from the sensor. Clearly too much thrust. When the magnet moved away from the sensor the engine would lurch. I am wondering if this might be part of the reason for Odyssey lurch? Too much play in the motor. I also noticed I could see the drive worm through a hole in the truck underside as if some one had tried to pound the old magnet back on the shaft and that is what caused the excessive play.

Pete

FWIW, I've seen a couple of magnet rings that were loose but not broken.  I used CA adhesive to stick them back to the flywheel and all was well.  My guess is that the glue you saw was an attempt at doing the same thing.

The motor shaft moving that much sounds more like a bad motor than too much thrust.  I checked three Lionel motors in my parts box, two with Odyssey sensors (broken ring however), and none had more than .01 end play in the shaft.  If you're able to move the shaft enough to disable the sensor, the motor sounds bad.

Had I realized there was that much play I would have just replaced the whole assembly. Replacing the magnet and sensor and you are 2/3rds of the way to a whole motor. Live and learn. I doubt the motor came from the factory that way.

Pete

I think you're right.  You can also damage the motor trying to pull the flywheel, sometimes those suckers are on there pretty tight.

Bob, are you refering to the ring that mounts on the original brass flywheel or the fix it magnet which is a one piece substitute? 

Pete