Keithley 2420

[hitecelec]

Hi All

Keithley model shows up -80 volts at the front hi lo terminal(without output on blue light enabled)as default even when the v source is 0 v.
when the output on is enabled the residual voltage -80v offset disappears and unit works ok.
However when the Output is programmed for High Impedance of state instead of Normal Off state unit works ok there is no offset of -80V at the output (without enabling output on button)
strange problem, has anyone encountered this issue.
I have checked all the ranges from mv to 60V , it is functioning ok.

Thanks in advance