1991 Lionel Warbonnet TMCC Problem

Is the run/program switch in the correct position?

Remove the shell and look closely.

Any loose wires? Connector screws all tight? Any smells of burnt electrics? Any burnt spots on the board?

Does the sound come on when track power is applied or only when the locomotive is addressed? 

RoyBoy - all seems tight; no smells, no burnt spots visible, except that I hesitated dismounting the mother and radio boards from the fuel tank cavity to examine their undersides. I'll have to do that, I guess. 

LOU1985 - Sounds come on when conventional track power (sans command box) is applied. With TMCC present, sounds come on only when engine is addressed. 

Thanks to both of you!

It's pretty easy to test the motors independently by just wiring the field coil to one brush, and the other brush to the center rail.  The other end of the field is frame ground, so that should spin the motors.  If that works, you need a little repair on the AC commander, likely the Q4008L4 triacs have been toasted.  They're cheap and readily available, not a difficult repair.

Thanks John. I haven't tested motors before. Can it be done safely without disconnecting the motor leads from the Commander board, or is that what "independently" means? 

No, you need to disconnect it from the AC Commander!  That's "independently".

Thanks again John (and RoyBoy), you put me on the right path. Looking where the brush and field wires connect, the field wire seemed a bit loose. Tightening of all screws with a Jeweler's driver, and now the engine moves! So both the motors and the triacs were good. 

Well, good wiring is certainly a first step!   A no-cost repair, my favorite kind.