Rear coupler not firing on F3 Railking PS2 3 volt engine

 Until the techs post.....

I would first look at the wiring very closely. Some times they break off right at the coupler. I imagine you've looked, so next I'd swap out a loose electro coupler to see if that one fires.

Sounds stupid but isn't the rear one a dummy for the hook-up to the other A or B unit??

Since he opens it, I have to assume it's not a dummy coupler.

I'd trace the wires back to the board, it's not uncommon for those to get pinched.  If so, they may be broken, or you may have cooked the FET that fires the coupler, those are pretty easily replaceable.

Did you do a feature and/or factory reset to see if that gets it's mind right?

Yes, I did both just to be sure and nothing changed. The wires appear okay and I did not see any breaks. Where would the FET be and what am I looking for?

Well, it's likely you won't be able to tell if it's cooked, although sometimes they do show visible evidence of dying.

I don't have a location for those, they're not mentioned in the ASC manual, all the lighting ones are located.  I'll get GGG knows where they are, I've never had to replace one as of yet, and since they're not documented...

Steam or diesel?  Some steamers have a switch in the tender to select either the rear coupler on the tender or the coupler on an auxiliary tender.

F3 Diesel and I checked the switch several times and no broken wires there either...

What is loco model number?  Is this a one or two-unit loco?  If the rear coupler in on the rear unit, there may be a tether issue.

This is the model number:           30-4187-1

It is from this set: F-3 R-T-R Freight Train Set

This is a single engine EMD style F3 Diesel engine. The instructions state nothing about the tether plug for running multiple units.

That is a PS-2 3V version.  I have seen MTH use a wire nut with the purple wire and the black wire for the coupler.  Purple is the voltage for the lights, coupler and one goes to the exterior harness connector for a dummy you can attach.

So check the wire nuts.  Check continuity on the switch, and makes sure the 12 pin is fully installed.  After that, it is the fet or a trace on the board that should be tested.  G

 Yeah sorry. It's nice to know the model number when discussing problems.

 Do a continuity test from the two wires that connect to your rear coupler to pins 2 and 8 on the 12 pin connector on the end of your PS2 processor board.

The purple wire George talked about is pin 2 on the 12 pin connector.   I run into these often with a broken wire at the coupler.  Unlike Lionel, the MTH is fixable at that point.

Jeff, instructions wouldn't say anything, since that's a single unit diesel.  If the loco were 2 units, they'd have to be an electrical connection for coupler & headlight on the rear unit.

Since the ASC manual doesn't point out the coupler FETs, where are they located on the 3V boards?

John, I have all that and will get it to you if needed.

Thanks Marty, I'd appreciate that.  I was surprised when I went to look for them and they weren't noted on the location diagram for the other lighting transistors and FETs.

Jeff, it appears you've only made visual inspections.  Do you have an electrical meter to make the continuity tests suggested?

If so, I'd first measure the electrical integrity of the coupler itself.  The MTH couplers I've seen have easily accessible solder blobs on the coupler assembly.  The resistance measurement reading should be a low number - around 2-3 ohms as shown.

If you get this reading at the coupler itself, you should get the similar reading where the 2 wires to the coupler attach to the PS2 board on the 12-pin connector (at contacts #8 and #2).  You need to insure making contact with the actual metal crimp inserts in the housing with the meter's probe tips.

If you do not have a meter, I purposely used a "free" Harbor Freight meter to show you don't need anything fancy.  I looked at your zip and it appears there are several near you.  You've probably seen these coupons in the Sunday paper. 

John, Look again.  The 3V fets are listed.  It is on the inside near the relay.  5V are not listed since it is a single dual FET and not really reachable. G

I did look again.  Here's all that are listed on page 14 of chapter 4 of the ASC manual.  Is there somewhere else I should be looking?

Thank you to all! I really appreciate the pictures and I had a least of the HF Voltmeters so used that. It looks like I found an iffy connector and once reseated after taking some time to measure all is well!

Merry Christmas to all!

On mine it is listed as a separate header just below Light FETs.  Header is "Coupler FETs" and List Q1 and Q2.  G

That's pretty odd, the next thing on that page in my copy is the locations on the power board.  Nowhere in the chapter does it show coupler FET locations.  I did a search in the electronic copy and nothing in Chapter 4 about those locations.

1 step fwd and 2 steps backwards.  Your right the electronic version posted on the MTH tech site is missing it.  The book I have from the course a few years ago clearly list it.

So much for the digital age and lack of version control, when the tools clearly make it so easy to do.

Back in my day, there would have been a clear side bar indicating any revision, a page revision date code and a Revision page documenting the changes. All done by hand.  So much for toy train documentation  G

I guess version control hasn't made it to our hobby yet.