Loss of Serial Signal?

The problem is the RailSounds audio board in the tender.

While it is indeed a complete RailSounds system, that particular version is Conventional RailSounds, and will not function properly in TMCC command mode.

The problem isn't technically the board but rather the chipset installed in it. To allow for things like CrewTalk and TowerCom to be usable in conventional mode, all the TMCC-related coding was removed as memory space was at a premium in those days.

The solution is to replace the RS4 audio board with something that's TMCC compatible - the good news is those are 98% of the RS4 audio boards out there.

As for the back-up light and rear coupler not functioning, I believe there are some jumpers that need to be changed on both the locomotive and tender motherboards when going from conventional to TMCC control. Also, be sure to restore/reset your R2LC with the proper code... 34 in the case of that locomotive and tender.

TRW

Thanks TRW!

Good news so far. Replaced the audio board as per paperTRW suggestion and got the railsounds that I expected. I now have a functioning rear coupler and a functioning head light that responds to AUX2. Still no rear light. I've been all over the engine but the problem is that I really don't understand how the backup light circuit works.  I've learner by searching prior threads that the R2LC controls rear light on/off via pin 7&8 but how is that signal processed. Does the 6108689131 DCDR process the signal and energizes a circuit via the tether harness to the mother board in the tender or is the signal sent directly to the tender where it is processed?  Once again, any help will be greatly appreciated!

Early TMCC RS4 it is sent via tether.  Is the bulb good?  Check tether continuity.  Basically, R2LC to engine mother board to tether to tender mother board to feature....coupler or RL.  G

I suspect these are close to the wiring of your unit, there's a wire that brings the backup light to the tender.  Should be pretty easy to trace out.

With the help of the diagrams I was able to trace the backup light to the engine's motherboard harness at which point I applied power to the yellow wire and the backup light illuminated so  I appears that the circuit from the mother board to the lamp is fine. I swapped out the R2LC radio board with a known good spare and the problem persisted. So since I have power to the motherboard, the R2LC is good and the harness wiring is fine that seems to only leaves the motherboard as the culprit.  I ordered a replacement from Lionel and when it gets here I'll post my progress.

I want to thank you fellows for your support.  I took on this project and a William's Train Master Command upgrade as a means to learn more about Command Control.  It's been frustrating at times but I've learned a lot!

If an ohmmeter and a visual inspection turn up nothing on the motherboard, I'd personally doubt it's actually the issue.  I wouldn't count on it solving the problem unless there's something I don't know here.

Well I finally got this all sorted out.  The motherboard had an open circuit from PIN 10 to the Tender harness connector.  I soldered in a jumper, reassembled and reprogrammed the (newly purchased from Lionel) R2LC radio board and nothing! I swapped out the R2LC for a ERR R4LC code C08 and all the features came up.  I had smoke, head light, backup light, coupler and RailSounds.  Question; are these boards returnable to Lionel and if not, are they repairable?

Something is odd about that.  The R2LC-C08 and the ERR R4LC-C08 should act identically in a TMCC or ERR environment.  I use them interchangeably without any issues.

If the R2LC you just bought is bad from Lionel, return it and get a good one.

Once again, thanks for the help!