This is a high precision digitally controlled current source for up to +-100mA of current and up to +-100V voltage compliance.
The current value can be programmed and controlled via BCD-logic. Additionally the current source can be controlled via a rear-sided connector with an analog voltage.
The HP6140A made its first appearance in the early 70s and its price tag settled in the low 5-digit Deutschmark-range.
It took quite a while till I could deal with the HP6140C again.
First I built a programming unit, similar to the original HP14533B.
I had to rely only on a single so-and-so decent picture of the device I found on a russian website.
Same as for the HP6140C decent manuals are seemingly unobtanium.
At least there is a slightly better scanned manual for the HP6130A, a similar working voltage source.
Also the descriptions in the manual are in part not supported by markers on the PCBs and many parts can not be identified due to missing printing on the top layer ... rather unusual for HP.
Well anyway ... with a bit of patience and helpers I managed to get the HP up and running.
Amongst these helpers are two diyed extender cards allowing me to check and adjust single PCBs ouside their drawers. I still have to diy more helpers to do the final adjustments.
As one can see from the pics there are dozens of trimmers and the trimming procedures are many and require serious effort. The possible precision is still today far above average though.
to be continued...