might be the pot.

Do you have a battery installed? Although some will certainly disagree, I have found that fitting a battery helps to prevent odd behavior that can be caused by intermittent power fluctuations from the track.

I believe the sound chip may need to be pulled and reinstalled to get it to seat properly. This has been a "somewhat common" problem posted here on the forum.

You'll need a "chip puller" to do it correctly.

Wheres gunrunner John?, I imagine this is his area of expertise. 

He'll probably chime in shortly.

Thank you guys for your hints, will check them out.  I do know not the handle boards while powered.  I appreciate your warning.

Will report back on results.

I missed this post, but Rick is onto it.  This is a pretty common issue, especially with older RailSounds boards.  The pins on the two PLCC chips develop some oxidation and then they have a poor connection with the socket.  Usually, simply removing them and replacing them in the sockets will solve the issue.

Do NOT try to take these out without a PLCC chip puller, you will almost surely break the socket, then you have a bigger issue!  you can usually get these at Radio Shack or many on-line places.

  Check your speaker and wires, pot assembly.

If there's no socket, I guess we can't blame the sockets!   I just had a recent Legacy locomotive apart, and it still had sockets.

SD70 M-2

It should be your Railsounds power board.  If you have another Legacy or TMCC locomotive, pull the known good board and put it in your engine.  Legacy and TMCC power board will be the same item.  I own several of those engines and have replaced several power boards.

It is always a good idea to pull the modular boards and reinstall them.

One more thing when putting the body back on.  When you lower the body over the chassis, try to spread the body with your fingers where it is going over the boards.  Those boards are shoe horned and can be moved very easy unless you do everything to prevent the body from moving them and causing no operation or the problem you have reported.

What wonderful advice, haven't had time to poke around and try any of the suggestions, plan to get to it Sunday.  Will update results.  Work with IC chips and have chip puller, thanks, John, for the heads up on that.  Will possibly post some photos to get definitive on what boards are which.  Thanks again for all the insight, much appreciated.

Again,  Railsounds Power board???????  The Audio boards on those engines are usually not a problem now that the sound chips no longer are removeable. 

My Northern did that going over certain parts of the layout. I put a battery in the tender and it never loses sound now. I think some of the engines have iffy roller pickup issues and the battery supplies the power if this the issue.

Update...  We believe that the mother board was putting pressure on the wire bundle underneath it and this was causing the problem.  Not sure what or why, but loosening the board and redistributing the wires seemingly has soved the problem.  Thanks for all the input.  Keeping fingers crossed.  lol.

I had a FA with RS that as the truck turned the motor mount spring plate which had an edge under the mother board shorted the volume pot pin on the bottom of the mother board and cut sounds off. I raised the motherboard to solve the issue.  G