My recommendation is the same as HandyAndy's. Spritz it down with electronic contact cleaner. In most cases that will solve the problem, IMHO.
I recently had a sticky e-unit in a 1947 turbine that I was able to correct by slightly bending the portion of the pawl that is above the armature (moving piece). It had a very slight bend, allowing the pawl to wedge against the e-unit drum. The drum was an NOS original.
A big-enough filter capacitor will eliminate all buzz; it just has to be twice as big for half-wave as for full-wave. How much is enough depends on the load and on how much rms voltage you need. Most of my locomotives do fine with about 5 millifarads; the 773 has 20 millifarads, because that model needs more voltage in any circumstances.
I can actually run full wave, to be compatible with AC operation, because I use a bridge rectifier. I just open one of two SPST switches to disable one or another leg of the bridge, blocking whichever polarity of half-wave I don't want; or I disable two legs to shut the locomotive off completely.
Bob Nelson
Bob,
Doesn't half wave cause more buzzing? I've used that trick to kick start some sluggish vibrotor accessories (and so has Lionel)
The reader who asked for advice in the Questions-Answers column for a sticking e-unit in a steam turbine may have one of the early models with a 671-50 horizontal e-unit, which has an internal spring to return the armature. If so, a faulty or weakened spring is one possible cause of his problem. (However, the 671-50 that I have in my Rail King Big Boy has never given me any trouble.)
Almost all my locomotives with traditional electromechanical e-units (including modern locomotives retrofitted with them) are modified to use DC for the e-unit coil and motors. I have had no more problems with sticking e-units after those conversions than before. And those I have cured mechanically, in several cases by shaving the notches flat as I described.
(I don't use DC for its own sake, but because I use half-wave rectification to be able to control two locomotives on the same track--sort of a low-tech TMCC. But never hearing e-unit buzz is a bonus!)
No experience with a magnetized E-unit, but I've read several places that DC current can magnetize one. The old O-Gauge locos use a universal motor design that will run on AC or DC. Running on a constant diet of DC for a length of time supposedly will cause the E-unit plunger to become magnetized.
Andy
What leads you to think that the pawl is magnetized? The usual assumption is that the armature is magnetized; but it is unlikely that either one is magnetized or would cause trouble if it were. Consider that the usual demagnetizing technique is to place the object in a strong alternating magnetic field, then to reduce the field strength gradually to zero. This is just what happens in an e-unit every time the track voltage is turned down to stop the train. So the e-unit's magnetic circuit is being demagnetized repeatedly in normal use.
An e-unit usually sticks for mechanical reasons. One common culprit is notches dug into the crotches of the drum teeth by the pawl. These catch the pawl after the upward stroke and prevent it from dropping back in the following downward stroke. The cure is either a new drum or shaving the notched teeth back to their original flatness. With care and a lot of patience, you can do this without removing the drum.
Never had to demagnetize a E-unit, but I have had a few that just didn't want to shift like they should. I picked up some electronic tuner contact cleaner spray at Radio Shack. Take the mechanism outside, and hose out the E-unit with the contact cleaner. Let it dry awhile and try running the mechanism without the shell. After a few stop/start cycles the E-unit should start cycling like it should. Unless there's some kind of mechanical problem with it.
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