Rear coupler swap

Here’s the plug provided by MTH.

Well, unless you want to start chopping the harness, you would want that connector, it's a Molex mini-SPOX connector.

The plug contains a resistor to act as a load for the coupler circuit in the PS3 diesel board.  Without a coupler or that resistor, the coupler FET will fail on the board.

Ok thanks. The mth instructions make no mention of installing the plug when swapping the coupler.

Forgot all about that issue, I've never had a PS/3 board that didn't have a coupler.  Must have been a stellar design team that made that circuit with a failure mode like that!

These are F3’s and mth provides a coupler that shortens the distance between another A or B unit. There’s a big gap with the rear proto coupler in place. Here’s the diagram in the directions.

@gunrunnerjohn posted:

Forgot all about that issue, I've never had a PS/3 board that didn't have a coupler.  Must have been a stellar design team that made that circuit with a failure mode like that!

This was an issue with the PS3 Railing AA sets that only have one protocoupler on the powered and dummy unit.  If run without the dummy, the same failure occurs, but not immediately.  Takes be quite a few hits.

I know nothing about the design!

This is applicable to any engine including PS-3 upgrades where the engine only has a front coupler.  Without the rear coupler in the loop, or the resistor, the front coupler operation is unreliable, and you may damage the coupler fet.  G

Thanks for all the info guys. I added the resistor.