Siemens DC Motor Drive

hi everyone,

i have a DC motor drive from Siemens made in 79 , the same year i was born ,

the thyristor trigger board's part number is 6dm1001-2la00-2 .

am facing a problem in calibrating the drive through the potentiometers on this board, also there's another board that has OP Amps i think it controls the feedbacks of the system like the tachometer and the field voltage availability with a lot of potentiometers that one of them controls the speed by raising the voltage on the output .

the system " motor and drive " are working proberly since 2 years , until someone made swapping for the boards with another drive .

my problem on the motor is that with load , the speed is falling from 750 RPM to 620 .

also the motor is heating .

i know i have to raise the current limit , and maintain the stability , so what am asking specificly is to know the functions of the potentiometers on these 2 boards or at least one of them .

thank you all.