Turns out it is the Frequency Valve, as JR had suspected. We have narrowed it down to the FV after diagnosing the Lamda computer and a few relays. The FV is not humming so it appears to be the "Weakest link." JR is ordering one, and should have it installed in a week or so. More updates to come....
Thank you JR for the education. I have a lot more to learn.
