Lights not working on MTH Diesel

Yes, the coupler and lights are on the same circuit in that there is a common voltage (called "PV") that connects to 1 side of each light and each coupler.  This PV voltage comes out of the #2 contact of the 10-contact connector and is distributed throughout the chassis/harness; it is usually purple wires.  The MTH PS2 diesel upgrade kit instructions:

http://www.mthtrains.com/sites...ction/50as15442i.pdf

has the following hard-to-read diagram.

That PV voltage is also used to power the motors and the smoke unit.  Does smoke still work?

Since the motors still work, I'd guess the PV voltage itself is OK but is not making it to the purple wires out of contact #2.  And if I were to make a guess, that puff of smoke was something akin to a fuse going up in smoke from excessive current.  So even if you find the weak-link so to speak (such as some BBQ residue on the board or on the connector) you need to find the cause.  When you were messing with the ditch contacts perhaps you introduced a short to the chassis/frame?

While things are crammed in there, it should be relatively easy to pull the 10-pin connector straight up from the housing on the board.  This can give you better access for visual inspection and/or to make continuity measurements using a meter.  For example, you should see no continuity between the contact #2 purple wires and the frame/chassis.

Hi pigfoot,

I have wanted to give you call since you first posted. Sorry to hear you "let the smoke out".

Stan will certainly help you out this one.

From one III in Woodbury to another, good luck on this. email is in profile.

Auf Wiedersehen

Here's one that may be easier to read.

Thank-you gunrunnerjohn, moonman, and stan2004 for the schematic.  I can not see any visible damage to the board or any broken wires.  Still no lights or couplers, everything else seems ok.  Where does the main power go into the 12 pin connector and how do you test it?

Pin 2 is the PV, which is the unregulated DC voltage that is chopped by the various incandescent bulb and coupler control FET chips.  If smoke, audio, and motor control are working, I'd look for a connection issue on the PV line.

I just had this problem on a diesel. I tested the light with a battery and it worked. So I bent the spring out a bit with a screwdriver, as GGG posted. It made the difference and the light came on when the shell was screwed on tight.

 Make triple sure no wires get in between the shell and frame to cause a gap.

of course that doesn't fix the coupler.

No power goes IN to the 12-pin connector per se.  They are all outputs (to lights, couplers, speaker).  These output signals come from the board itself.

If everything else works (motors, smoke, sound) but couplers and lights don't, I don't think you are getting PV at pin 2.  If you have steady hands and your meter's probes aren't too "fat", probe the contacts on the 12-pin connector as shown.  Measure DC-voltage between pin-10 (circuit ground) and pin-2 (the elusive PV voltage).  With the engine powered, the measured DC voltage will be about the track voltage plus or minus.  Both of the contacts usually have more than 1 wire coming out so it can be tricky to access metal of the crimped contacts with the probe tips.

Hello  Stan

I got no dc voltage at pin 10 and 2

Can you pull the 12-pin harness/connector straight up out of the housing to expose the male pins?  I just grab the entire bundle of 15 or so wires and pull up maybe with a little wiggling.

Then, inspect the both sides of the pin 2 (what's on the board and what in the harness) for anything odd looking.  Then with power applied, carefully probe between the now exposed male pins 10 and 2 to see if you get a DC voltage.  In other words, we're working backwards toward the source of PV.

Obviously you'll have no sound since the 2 speaker wires came out.

Edit: picture added.  This is obviously an un-powered loose board on the bench but was what I needed to do to take photo with camera in one hand, etc. etc.

I removed the harness and saw nothing odd on either end.  I did not get any dc voltage between pin 10 and 2.   

Just to confirm, you are getting smoke?  Not just the smoke fan whirring, but actual smoke coming out?

The next step is to carefully inspect around pin 2 and the housing.  Here's an example of a blown PV printed-wire from a repair I did.  I'm not saying this is the only place to look but what it might look like.  In this case the failure was hidden in the gap between the 12-pin housing and the 4 and 8 housings next to it.  You'll know it when you see it!

If you are not getting PV at pin 2, then I'd say you're going to have to remove the board set from the engine.  I suppose you need to start thinking about sending it to one the MTH techs if this is getting too involved.

Separately, I still believe you need to track down what I believe must be a short in the harness that took out PV.   With the 12-pin harness pulled, did you 'ohm-out' the contact #2 at the connector to the engine frame/chassis?

I had one of these with the PV trace cooked, turned out a little jumper was all that was required.

Still no power at pin dc volts at pin 10 and 2.  What should the voltage be?  I got no continuity between the #2 and the chassis.  If I can't figure it out can anyone suggest a repair shop in the South Jersey area.

You should have NO continuity between any of the signals on the board and the chassis except the incoming power.  There is no common ground with the PS/2 boards.