I have a Lionel 6-28298 CSX AC6000 that the couplers do not open up.   When I fire the couplers with my Cab-2 remote I can hear the clank/chuff noise so I know the R4LC board is getting the signal.  I can sometimes hear a very faint buzz from the electrocoupler.  I measured the voltage at the coupler connection on the motherboard and I'm only seeing a brief 2.5 VAC.  I compared that to another one of my slightly newer AC6000s and it fires a hefty 5 VAC at the coupler.   What component would cause the voltage to be that low?  The loco has a separate AC Regulator but I assumed that was to power the smoke unit only. 

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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.

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.

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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.  

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