You should power it on, wait for a while, and then run signal path compensation. It will likely give some error. That means something is wrong. If you don't want to go through the effort of repairing it, you may still be able to use other channels for triggering. This forum also has a section for selling things.
Thanks for the advice. I ran SPC.
It returns 4 errors - duplicated for all 4 channels.
"ERROR: Characterized values out o"
"Ch1 trigger gain"
I don't know what the truncated line is, but I assume out of range.
It sounds to my simplistic mind that I changed a setting and wherever it is stored in memory is not accepting the new change or it is not getting updated.
It also says:
"Warning: Varigain setting beyon"
"CH1: 1.073>1.049"
This message only appears for Ch1 and only appeared one time - the others repeat every time.