Alright, I've done some more diagnosing. How can I be sure whether the problem is the 990 or the PF60? Here are the clues so far:

990: I've tried two different cables with the same results. My voltmeter tells me there is a 1.2 mV (yes mV!) differential when the 990 is on, and 0.0 when it is off, between the + and - of the cable plug. I did try resetting the 990 to factory defaults, and it didn't fix it.

PF60: It supports trigger either by 1/8" plug or by AC power plug. I know the AC method works, because that's what I was using with my old Sony preamp. I've never used the 1/8" plug until now. If I try to trigger it with a 9V battery connected to the other end of the cable simulating the signal that's supposed to come from the 990, it doesn't work. I'm not even sure a 9V battery should work as a trigger -- should it?

I don't have another device to use either as a triggerer or trigeree to verify one of these devices is working. I'd hate to send in my new 990 for repair and not it be the problem.

Any ideas how to diagnose which unit is the problem? Or is my voltmeter measurement pretty definitive that the 990 is defective?