Thank you normandinf, for sharing your experience .
in our 6487 , the voltage source part behaves strangely . when i start the instrument, the source shows -8 V. but if i switch on voltage source and cross -8 v then it shows the actual voltage and then i can increase it to zero or even positive. may be as u say it is damaged. ( dissaponited :headbang: my experiments is waiting for the instrument ).
i have written to keithley .
thanking you
ranjini