(Because of a totally unrelated reason) I was checking the electronics units for the upgrade. And I realized that the electronics units at the test stand have not been properly powered.

I found that the AA/AI stack at the test stand (Attachment 1) has an unusual powering configuration (Attachment 2).
- Only the positive power supply was used / - The supply voltage is only +15V / - The GND reference is not connected to anywhere.

For confirmation, I checked the voltage across the DC power strip (Attachments 3/4). The positive was +5.3V and the negative was -9.4V. This is subject to change depending on the earth potential.

This is not a good condition at all. The asymmetric powering of the circuit may cause damages to the opamps. So I turned off the switches of the units.

The power configuration should be immediately corrected.

1. Use both positive and negative supply (2 power supply channels) to produce the positive and the negative voltage potentials. Connect the reference potential to the earth post of the power supply.
   https://www.youtube.com/watch?v=9_6ecyf6K40   [Dual Power Supply Connection / Serial plus minus electronics laboratory PS with center tap]
2. These units have DC power regulator which produces +/-15V out of +/-18V. So the DC power supplies are supposed to be set at +18V.