[Orion] Orion no Tx, no main Rx

[Martin AA6E]

Folks,

I've had years of mostly happy experience with my barefoot Orion.  So 
recently decided to install an SB-220 amp.  This one has a number of the 
AG6K mods installed for QSK, bias cutoff, low-level keying control, 
anti-parasitics, etc.

I installed the amp and was able to load it up and operate CW on various 
bands and antennas.  No sign of trouble, no RF in shack.  The amp is 
using the Orion's Amp Key output.

What has happened twice now, is that the Orion (1.373b5) is hung up in 
an odd state:

-No main Rx signal (normal noise, however).  Sub Rx is fine on same VFO 
and same antenna input.  No change in main Rx noise with preamp or 
attenuator settings.  Main Rx hears nothing on either antenna input or 
on Rx ant.

-No Tx level. (normal CW sidetone, however)  When you key the rig, the 
Amp Key output is asserted and the panel meter goes to zero.  There is 
no RF out.

At first I thought I had somehow blown something in the Main Rx system 
and was contemplating a shipment to TN.  (Though when the Tx was 
working, I had no indication of trouble with the amp on or amp off.)

I tried all the known Orion resets, power, master, battery, etc.  No 
effect. Changing bands, modes, disconnecting amp control has no effect.

But then I was fiddling with the buttons (couldn't tell you which) and 
the Rx came back!  That was yesterday.  Today the problem has come back...

It kind-of feels like a dead early IF or mixer stage, and I kind-of 
remember having this experience one time a while back without the amp.

So before starting wheels turning with TT, I thought I would ask the 
net-mind for its wisdom.  Is this a known problem?  Can you think of 
other tests to try?

TIA

73 Martin AA6E