Oh man did I fry another PS2 board?

Here's the relay I'm using. It's the 12VDC relay.

Also, I let everything sit for a couple hours, and was able to re-add the engine again and without the coupler all seems well.

An going to raid some of my shells for a PS2 coupler and give it another try.

UPDATE: I've put in a PS2 coupler without the relay and everything seems to be functioning properly.  However, I tried to wire up a rear backup light (white LED with a resistor in line) but when hooking up to the rear backup light pin and connecting to the PV circuit, it wouldn't light.  Checked polarity and it was good. So I checked my voltage feeding the LED leads in the tender, and it read 24.2V (!)

I knew that wasn't right so I thought maybe I screwed up soldering to the tether PCB or something, or maybe I blew some regulator on the board...  I used a pointy probe and checked the voltage right on the PCB harness at the PS2 connector between the rear backup and PV pins, and it too reads 24V still.  Just to make sure, I checked each of the leads for continuity to body or track and nothing is grounding or shorting to the track or shell.

I thought then maybe there was some problem with the PV entirely, so I checked the headlight pinout and PV, and read 1.7 volts (What?). The front headlight is the OEM headlamp (incandescent) which I understood to be 6V form the loco-sound engines.  So I don't even know how it lights up with 1.7 volts.

So I'm convinced I'm doing something very wrong. Maybe my meter isn't reading the PWM correctly and is just tagging the peak voltage of the PWM? But how does that explain the 1.7 volts for the headlamp?  I've verified it's set to DC (sometimes I screw up and have it set to AC).  Except for the rear headlight, the loco seems to function just fine though.  Any thoughts?

Jeff, I followed your process hoping someone else would chime in.  I haven’t had issues like yours.  Your thinking seems logical to me, and I agree; “24.2V (!)”. What??  The only time I had trouble with the lights, I substituted the light harness from a similar engine, and all was A-Okay!!

I hope someone who has dug into these boards will see your post and reply..

The voltages you are reading are PWM (Pulse Width Modulated) voltage and won't read on most multimeters.

@gunrunnerjohn that's good to hear.  I figured it might be the case. I had to return my Fluke to work and I bought a $100 Klein multimeter, but I guess it doesn't have the same sensitivity as the Fluke does.

In any case, something's still not right.  I'm pretty sure I pinched a wire or something when closing up the loco shell (the PS2 is in the loco, not the tender).  Started up and ran OK for a bit, but then I couldn't turn off the smoke fan. I turned smoke off in the DCS and the resistors stopped heating, but the fan kept running.  So I switched off the manual switch to the smoke circuit but the fan kept running. Then the headlight started flickering and went out as well.  So I'll have to pull it apart and check for a pinched wire now somewhere between the fan and headlights.  Or worse, there's some problem with the grounding in the card itself?

I thought I could do this one pretty quick given the same harness setup between the loco-sound and the PS2 3V card, but alas the tight squeeze in the shell is making it a tougher job than I hoped.

I think it's time to test the PS/2 board independently from the wiring.  The PS/2 boards primary Achilles heel is shorts to ground or between leads.  With the board in the locomotive, it does take a bit of care, I put one into the Q2 recently to replace a dead 5V board.  Even though it's a big locomotive, it was an interesting fit to get it in there.

@gunrunnerjohn : Would I just unplug everything and check for continuity between each of the pins on the 12-position harness and smoke harness to the PCB ground on the board?  If there is continuity between any of those, then = bad?

Also, I'm not using any of the ancillary lighting harness (8-pin).  It's not even in the loco, and nothing is plugged in there at all.  That wouldn't cause any issues, would it?

Missing plugs aren't an issue, you can fire up the P/2 board with nothing but the 7-pin connector attached.  It won't do much, but you won't hurt it.

Top suspect is either a short to ground or a short between leads like motor, smoke motor, smoke resistor, or a lighting output.  An open isn't going to do what you see.

Finally dug back into the loco.  PS2 board is fine, The headlight wire got pinched under the headlight bracket and pulled one of the fan motor wires free and it was grounding against the headlight bracket.

All cleaned up now and runs like a champ!  Honestly, except for this stupid pinched wire, this Loco-Sound conversion was the easiest PS2 upgrade I've done (I always use harvested harnesses and PS2 cards, I haven't used an actual PS2 upgrade kit).  It's crazy to me that the Loco-Sound configuration with the tach, the wire harnesses already being mostly correct for a direct plugin to the PS2 card, and size of the locosound card being pretty close to the PS2 card...it's almost like MTH developed locosound knowing that it would be a prime candidate for a card swap later in life.  Way easier than the PS1 upgrades I've done.

I'm glad it was only a pinched wire.  It's so easy to let that happen.

@Jeff_the_Coaster_Guy posted:

it's almost like MTH developed locosound knowing that it would be a prime candidate for a card swap later in life.  Way easier than the PS1 upgrades I've done.

I believe it was developed with or after the 5V PS/2, so they just tried to use common parts wherever they could.  Truthfully, I wondered why it was ever done, I can't imagine it saved much in manufacturing costs over the PS/2 board.