RIO GRANDE UP HERITAGE LEGACY SD70ACE 6-28377 Uncoupler Pocessed

If it is the modular one, the R4LC radio board. G

If you press down on the resistor it lights slightly. Shooting from the hip, maybe you have some designed for 120Vac, so the resistors would be much higher, and then the resistance (or resistance and capacitance) of your hand is allowing enough milliamps to pass thru to see a bit of light???

If you press down with something insulated like the handle of a plastic spoon, and the same thing happens, there goes my theory.

Randy, I suggest you remove the cab from the Rio Grande and look around specifically for any pinched wires.  This happens frequently during reassembly.  The coupler wires are typically both black.  Try and follow the wires to the board they are connected to (R4LC according to G) and remove and reconnect there.  See if that corrects.  If not, then I would swap R4LC boards between your 2 different SD70s and see if the repeated uncoupling problem migrates with the board.   If so, then replace that board. 

Here is a link the Lionel site to order parts.  They seem very light on the parts for your Rio Grande but all the parts are listed under the #1870 Katy:

 Lionel Parts - #1870

That was my thought as well: swap board and see if the problem follows the board.  GGG was kind enough to get me to the proper board, but the link from you for the replacement is really awesome.  I hope to get to this over the long weekend.  I have this pesky Arduino controlled turntable that I am wrapping up that is sucking up all my time (a little more hardware there, update the software, and repeat).  I keep coming up with too many great ideas...

Thanks, guys, for the advice!

-Randy

Reprogram the engine with aux code 2.

Marty Fitzhenry posted:

Reprogram the engine with aux code 2.

I tried that already.  Interestingly enough, that worked for a short while (like an hour or two, if I remember)....  I think the next time I went to run the engine it started acting up again.  Very strange....

-Randy

If reprogramming worked for a short time and then reverted to no coupler again, replace the R4LC.  It must be forgetting it's programming.

John is right.  If what you did worked for a time, your R4LC is defective.   What are you using for a transformer?

gunrunnerjohn posted:

If reprogramming worked for a short time and then reverted to no coupler again, replace the R4LC.  It must be forgetting it's programming.

It's not that it doesn't have a coupler (or forgets about the coupler).  The coupler randomly opens and closes -- jitters.  You can directly address the coupler with the remote and it will respond (open).  Close it and it will open on it's own.  It's being pulsed randomly by the controller board it seems.

I still haven't have a chance to tear into it, so it's still guessing at this point.

I appreciate all the advice!

-Randy

Well, clarity is key when you're describing issues!  This is what you said...

Randy Owens posted:

Marty Fitzhenry posted:

Reprogram the engine with aux code 2.

I tried that already.  Interestingly enough, that worked for a short while (like an hour or two, if I remember)....  I think the next time I went to run the engine it started acting up again.  Very strange....

-Randy

I'd have to be a mind reader to know that your latest description is what is really happening.

Now that we have a clearer description of the issue, I'd do this.  First, look for ANY shorts in the wires coming from the coupler to the motherboard.  Next, install a 1uf 50V non-polarized capacitor directly across the coupler inputs on the motherboard.

gunrunnerjohn posted:

Well, clarity is key when you're describing issues!  This is what you said...

Randy Owens posted:

Marty Fitzhenry posted:

Reprogram the engine with aux code 2.

I tried that already.  Interestingly enough, that worked for a short while (like an hour or two, if I remember)....  I think the next time I went to run the engine it started acting up again.  Very strange....

-Randy

I'd have to be a mind reader to know that your latest description is what is really happening.

Now that we have a clearer description of the issue, I'd do this.  First, look for ANY shorts in the wires coming from the coupler to the motherboard.  Next, install a 1uf 50V non-polarized capacitor directly across the coupler inputs on the motherboard.

Thanks, John.  My First post said this:

Make sure the brake switch on legacy remote on the left side is not all the way down