I am building up new patch clamp setup (Axopatch 200B, Digidata 1440A). I had right signals with both model cell and patch electrode. I decided to decrease a noise and grounded all the electrical devices. Noise was much smaller but instead of seal test in bath mode now I am getting strange flat line. Is it possible that ground loop happened and could it damage the amplifier? I disconnected all ground wires but it did not change anything.

Please see pictures of model cell in bath position before and after ground is connected.

Axopatch 200B parameters:

Pipette offset: 5.2

Zap: 0.5 ms

Series resistance comp. prediction/correction: off

Lag: 1 micro sec whole cell cap: off

Series resistance: 0

Holding command: off

Seal test: on

Meter: I

Mode: V-CLAMP

Config: whole cell (β =1)

Output gain: α=1

Lowpass Bessel filter: 1KHz

Leak substruction: off