[TenTec] Orion and amplifier fault

[Bruce Small]

I need to tap the collective wisdom of this group regarding an 
interesting problem.

I have an ACOM 700S solid state amplifier that is driven either by an 
Orion (565) or an Orion II (566).

When I use the 565, the amp faults on 10 meters only. The protection 
fault indicates high SWR and excessive drive current. This happens 
regardless of the amount of drive power from the Orion, even with the 
PWR control turned all the way down, providing about 6 watts of drive. 
On CW, the fault occurs on key-down, while on SSB and FT-8 the amp 
faults on key-up, at the end of a transmission. Engaging the TUNE button 
does not produce the fault. All bands other than 10 meters work normally.

Using the O II, none of this behavior occurs, and the amp plays happily.

Steps taken without solving the problem include:
*Replace coax jumpers  (they needed it anyway)
*Replace arc plug in lightning arrestor
*Remove all components from the signal path (watt/SWR meter, tuner, coax 
switch, lightning arrestor) and connect directly to the coax run to the 
antenna
*Connect to a different antenna fed through a separate coax cable
*Control the amp using Keying Loop 1, Keying Loop 2, or the Amp Key output
* I don't have a good oscilloscope, but to the best of my ability to 
observe, the CW waveform was well-shaped and didn't show any spikes in 
power.

All of this points to an issue with the Orion on 10 M - what else should 
I look at?

Thanks & 73,
Bruce KM2L