SOLVED: Lionel Railsounds 6 Motherboard Bad?

Not much on the MB to go bad, take it out and do a close physical inspection.

Thanks GRJ.  I removed the 4 mounting screws and flipped it up to inspect and didn’t see anything obvious.  I will go ahead and disconnect the board and do a closer inspection.   Next I will swap motherboards with another working unit to confirm that is the location of the trouble.

Maybe we have a bad/cold solder joint on one of the pins of the motherboard.  Reason is that when it was not working I barely touched/moved the RS6 sound board and it worked for 2 seconds.   I can’t get that to repeat though.

A potential piece of the puzzle was that I had adjusted the volume potentiometer 5-10 seconds before the sound went out.   Could a bad pot cause these symptoms?   What is the resistance range?

The pot is 10K linear taper.  The pot is a very common failure item.  Try some contact cleaner on it.

I checked the pot and it was 10K each way and smooth.   I swapped a working motherboard to this loco and no change.   I disconnected the SFC1 board just in case it was drawing things down and no luck.  I don’t believe the DCDS is causing it because it’s driving the wheels fine.   I don’t think it’s the radio board because the loco will respond forward and back.   I don’t think speakers because 2 of them and I can hear the tapping /pulse sounds.   Those pulses increase frequency when trying to honk horn or ring bell.  I’m really at a loss for what to check next.   Ideas anyone?

I'd be tempted to swap the R4LC and see if that changes things.

Ok GRJ, going after the R4LC next and will report back.  Thanks.  

I swapped in a known good RCDR and problem remains.  So far the boards are all working.  Inspecting the wires I see nothing that has been pinched or any corrosion.  

You need to start eliminating stuff one at a time.  I would stick a totally different speaker in first and work back from there.  On a plain transformer, the sound should come on even without any serial data.

OK GRJ, I'm on it.  BTW, I did ohm out the speaker pair (two in parallel) and found 7.8 ohms.  I measured a working unit and it checked the same. 

Please don't mock me for making such a basic suggestion, but have you verified the program/run switch is in run?  I know, I know...just don't ask me how I have experience tearing an engine apart to diagnose only to realize that switch was in the program mode...

A little more engine-specific: These have die cast shells and die-cast stanchions for the handrails, but to insulate the handrail grab iron for use as the signal antenna, there's a little plastic tip on each stanchion that can easily slip off.  It may be worth verifying the antenna is good and the hand rails are not grounded to the body anywhere.  This led to various issues on my ES44ACs.

Thanks Woody for the suggestions.  I'm very stumped on this one and looking for all the help I can get.

Right now with the shell removed the handrail antennas are not in play.

I did verify the Prog/Run switch position visually as well as with a meter.

BTW Woody, the reason the shell first came off was because only horn and bell was working, no crew talk or engine revs.  Somebody didn't check that the Railsounds Switch was off. 

So you have swapped the railsounds board, railsounds power board, R4LC, and motherboard into another engine, correct?  Have you tried swapping the known good boards from the other engine into the problem engine?

Actually been swapping known good boards into the bad loco.   I did also try the suspects RS and RS Power boards into the good loco and they worked.  

More things I tried:  I removed connector to DCDS and no change.  I removed connector to tach and no change.  Only connectors I have right now on MB are J1(Power and serial) J2 (speakers and pot) and J3 (battery and RS switch).  

Chalk up another one for @gunrunnerjohn.  His last parting recommendation was start at the speaker and work my way back.   Well, it was the speaker.   Actually one of the speakers was loose enough in the fuel tank that it rotated and allowed a terminal to touch the chassis (speaker hold down bracket).  Earlier when I checked speaker resistance it was wire to wire at J2 connector.  I did not check to ground.

Just needed to slightly rotate the speaker and tighten.   Now it’s time to get this beast and the test loco back together.

Thanks again Gunrunner!!

Well, it was in the area of the speaker.   Glad it was an easy one.

Lucky it didn't take out the amplifier on the unobtainium RS6 board, shorts to frame ground are frequently deadly to the audio board.