MTH loco suddenly drops sound volume when reversing

Well, the top suspect might be the volume pot, next the speaker.

Thank you for taking the time to reply. I cannot make it drop volume by tapping it only restore original volume with a tap. I would think a mechanical problem like a volume poty would misbehave both ways and for the life of me I cannot think of a reason it would do this only when the locomotive goes into reverse. Speaker is fine.

Thank you again. Still looking for the definitive answer.

Not a tether issue for PS-1.  Everything is in tender for sounds.  What are you tapping to get volume to raise?  G

Discovered it tapping the tender shell top with the tender fully assembled. Pulled of the tender top and played for a while but of course now that i want it to happen to try some things, it has not dropped again yet.

Is the speaker over a truck attaching screw.  I really can see no reason why reverse only would do this.  But if the screw to hold truck down is under speaker and comes loose it can touch cone and restrict vibration. 

Check that, check solder joint to speaker and 2 pin fully connected to board.  Cycle volume pot and make sure three pin fully connected to board.  G

Thank you very much. I had checked the speaker, pulled and reseated the pin connector on the board. No change. I had set the volume pot at different levels in case it might be a "dead" spot on the winding. Right now, i cannot get it to misbehave but i have it ready to play with again as soon as I clear some time.

I wanted to thank everyone for their help. It seems to be the volume pot. It is not a dead spot at a particular volume, it was not a loose external wire. It seems to be something inside the volume pot. When it finally began to misbehave, tapping the volume pot itself restored the volume but not always. Volume pot to be replaced.  Sold it to someone who already had the smoke unit board and wants to do the repairs himself. Happy 2024 to all of you.