[Elecraft] K144XV repeater setup problem

[Lew Phelps K6LMP]

I (finally) got my K144XV internal 2 meter transverter yesterday, and installed it last night. 

It appears to be functioning normally, but I am unable to ping any local repeaters. Here's what I have:

I am getting 10 watts out, per an external wattmeter, with low SWR.
I have the repeater shift appropriately set at -.600 or +.600, depending on which machine I am trying to hit.
I have the PL tone set to the correct frequency for the given repeater.  I have PL turned on (using VFO B knob after pressing Tone and entering the correct PL tone)
Using the ALT button, I have set to transmit at the designated offset of - or +, depending on repeater.

The screen display shows FM T and  -or + as appropriate.

I can hear output from the repeaters without difficulty. But I can't key any repeaters. I suspect that, for some reason, I am not sending the PL tone. 

What am I missing? Is there another piece of the repeater setup procedure that I have not found in the documentation?

Thanks in advance.

Lew K6LMP