Hi all,
I hope can find some help here.
I've a Keithley 197 which shows an always positive drift on the last 2~3 digits, It's seems to stop after ~1 hour if I don't touch any of the front panel controls.
This happens on any range.
I've started to do check of internal nodes and the only weird thing I've found is -V node at -14.5V, it's showing ~200mv of 100hz rectifier cap ripple. This node, from schematic, should be -15V see R132 and VR105 (which should be a 15V zener)
R132 is at nominal value and VR105 was tested good, so I guess there is some unexpected current request from -15V that is able to bring the node too low to make VR105 work.
All other voltages seems clean and at nominal value (-9V, -6.4V, +5V A and D, +10V)
Moreover I've was not able to spot any issue in the measure path or A/D waveform.
Please let me know if -V is expected to be -15V & clean, and any of your thoughts on this issue.
Regards,
Fabio I.