AC6000 Couplers Won't Open

The couplers are fired directly from the R4LC on that model.  First thing, check the wiring to the couplers and verify all is well.  Next, I'd check and see if there's an issue with the pickup wiring to the motherboard.  Although most of the locomotive functions will operate at around 11-12 VAC, the couplers require at least 15-16 VAC.  If the MB is getting full voltage, I'd try swapping the R4LC.  If it works in another locomotive, or a replacement works in this one, you'll need to replace it.

That’s great advice.   I will check and report back the results.   Thanks.  

Does the coupler fire from a triac? So trying to read the voltage with a meter is not going to show the correct value?

Yes, the R4LC uses a triac, the same as the R2LC.  However, the coupler triacs pass full wave AC for the couplers, so you should get a decent reading.

Per GRJ's direction I inspected the wiring and found no issues.  I then swapped the R4LC from this loco to a functioning one and the problem moved with the board.  Looks like I need to purchase a replacement board unless there is any known magic out there.  I'm not afraid to solder in a new triac or cap but I would need to know which one(s). 

Thanks GRJ for the pinpoint advice!

The R4LC triacs are in the same position as this R2LC picture.  The coupler triacs are sprinkled between the others.

My technique for removing these is to first bend the triac back and forth right at the body and break it off, leaving the leads.  Then I heat the rear of one of the pins until the solder melts, sometimes a bit of extra solder helps.  Once it's really melted, I quickly RAP it on the bench component side down.  Normally the lead and the solder leaves the hole, ready for a new lead.  Repeat for all the leads and then solder the new triacs in.  If a lead is balky, you can just grab if from the component side and heat it up and pull it out. 

The MAC97A8 is the current part number for the proper part, the MAC97A6 is a slightly older version.

I got home tonight and looked a bit closer at the board.  I said I wasn’t afraid but now I am.  It’s just a little past my skills to solder in replacement triacs in  this much congestion.  I plan on ordering a new replacement.   Thanks GRJ for pointing out the culprits.  

Send your board to John. He can replace the triac at a fraction of the cost of a new board.

I need to check my voltage, I have the same issue with a new Lionel Bi-Polar.  Makes the sound and all but no opening.

update: where I was trying it, 14.35v so too low.  At the feed it is 15v, I am using DCS Legacy for supply so I will need to upgrade I think unless I can find a way to bump the voltage up.  I will try the couplers right at the terminal later today too.  

How did people even “do” hobbies before the internet??  My front coupler works fine now and the rear does also just not every single time.  I send it around the track and when it comes by the coupler is open so maybe the moving around is enough to jostle it open.  I am guessing it will get more reliable with time but since it is a bi-polar, the front one will do just fine for now. (I love bi-directional units!). I am reading 18.4v which should be OK I am guessing for DCS and Legacy?

So very happy I did not have to send it anywhere.