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Problem - I have replaced the rear coupler on this unit only to have the replacement fail.  I used a spare MTH coupler from a dead PS2 5volt locomotive.

When checked with a multimeter the out put of the board to the coupler is in the 2.1VDC range (fluxuates to a lower value if I repeated press the coupler release button).  I of course get the coupler release sound, and when tested with a grain of wheat buld the bulb lights up.

If I replace the coupler with another one source for the other end of the dead PS2 5 volt loco, it works - I jumperd this one in and fired it 3 times, then disconnected it.

Attached are pictures of the board:

 

Thanks

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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.

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