[Elecraft] K3 - RTTY Mark frequency not at 2125, as set (FSK)

[conwell at aracnet.com]

I tried setting up FSK rtty today for first time in a long while, and 
found I had a problem.

I have a pair of K3 rigs on the desk.  No trouble with one.  On the 
other, Mark tone is sent higher than 2125.  (It's high enough up that my 
2d rig can't decode the TX signal.  Maybe around 2600 Hz)

The Space tone may be high too - my ear can't discriminate.  (But in the 
X-Y scope pattern of the TX signal, as received on the 2d rig, the tones 
are at right angles - if that means anything...)

Thinking it might be a TX AFC problem, I disconnected the computer.  
Same result.

When I long-push PITCH, the rig speaker gives the 2125 HZ tone.  But 
when I touch XMIT, the rig gives a different - higher - tone.  (In 
contrast, with the other K3, both buttons yield the same tone - a tone 
which matches the 2125 Hz output by the problem rig when I press its 
PITCH button).

I tried updating all firmware (e.g., from 5.10 to 5.35).  But issue 
persists.

Ideas?

Thanks,

/Bill, K2PO