Electro Couplers failing in a K-Line K3380-3768IC Torpedo

Well, the problem is, the PS/2 coupler is NOT compatible with TMCC coupler outputs!  You can use a PS/1 coupler or the TMCC/Legacy coupler.  Measure the resistance of the coupler, if it's in the 2-3.5 ohm range, it's NOT compatible with TMCC.

Thank you sir, that was exactly what I was looking for.

Glad to assist.

So with my multimeter when measuring resistance;

When I measure the resistance of my leads by touching one to the other I get 0.3 -0.7.

When I measure resistance across my coupler I get 2.3 to 2.6.

So I would subtract my leads resistance range from the coupler resistance range and yeild a coupler resistenance of

1.9 to 2.0 to account for artifact error? 

Concluding that:

my tested coupler has a resistance of 1.9-2.0 ohms and is not compatible with the TMCC on my Torpedo.

Yes?

Yep, that's a PS2/3 coupler, and it'll either cook it or take out the R2LC coupler triac.  You need the coupler that measures at least 5 ohms.  The older Protosound 1 couplers (that look just like the PS2/3 couplers), are suitable for TMCC and I use them all the time.

As far as your ohmmeter readings, it could be just a lower cost unit that doesn't have really good low scale ohm accuracy.  Both of the Fluke meters I use will actually get to zero when the leads are in good contact.  However, the cheap Harbor Freight meters typically have a couple tenths of an ohm with the leads shorted, nature of the beast.

Its an older Craftsman Professions model # 73754 which has seen hard use on my boats and cars.  The leads have been cut and probes soldered on and off over the year so between the original quality and ware it is what is is and I live with artifact error.

Again thanks for sharing the information.

Yep, I have an ancient Fluke that I've retired to my car toolbox as well.  Still works (mostly), but the resistance measurements are starting to get a bit flaky.  It served me over 20 years, so it doesn't owe me anything.   However, I do have a need for fairly accurate measurements, so I count on the new Fluke that is spot-on.