Model 640 & 640CC Instruction Manual
D01206676
Revision A February 2016
35
in the mounting frame. The length of resistor extending past the connecting
strip should be approximately even on both ends.
4.
Seat the resistor securely in the slot in the mounting frame. Use care to avoid
damage to the resistor. The top surface of resistor must be level with the top
of the mounting frame.
5.
Use a smooth, round rod (such as the round shank of a screwdriver) to rub top
surface of resistor, burnishing resistance wire lightly so potentiometer slider
will slide smoothly with minimal noise.
6.
Rotate potentiometer slider by hand. Assure that slider makes contact with the
resistor during its entire range of motion. If necessary, adjust slider by
bending it up or down.
7.
Replace shaft bearing retainer and check the potentiometer mechanism with a
calibrating device.
Potentiometer Mechanism Spring Replacement
12.8
The spring should wind tighter when the slider is moved in the
counter-clockwise direction.
1.
Remove shaft bearing retainer and potentiometer Slider.
2.
Remove old spring.
3.
Install new spring.
4.
Replace potentiometer slider.
5.
Loosen the three spring adjuster clamp screws on underside of the frame, but
do not remove the screws.
6.
Rotate the spring adjuster until the potentiometer slider lines up with the front
contact strip. Tighten adjuster clamp screws.
7.
Rotate potentiometer slider by hand. Assure that slider makes contact with the
resistor during its entire range of motion. If necessary, adjust slider by
bending it up or down.
8.
Replace shaft bearing retainer and check the potentiometer mechanism with a
calibrating device.
