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Curtis PMC 1204/1205 Manual
MAINTENANCE & ADJUSTMENT
POTBOX
Maintenance
Potbox maintenance is similar to controller maintenance: inspect for
integrity of connections and mounting, and clean (with a moist rag) as
required.
Adjustment
Curtis PMC potboxes are factory set and rarely require user attention. To
test and adjust, connect an ohmmeter to the potbox wires and use this
procedure:
1. With the spring holding the lever arm against the return stop,
the resistance should be less than 50 ohms. Slowly move the
lever. If the resistance abruptly starts to increase when the lever
is 3 mm (1/8") from the stop (1.5 mm [1/16"] for potboxes
without the microswitch), no adjustment is needed.
2. If adjustment is required, loosen the screw holding the lever on
the pot shaft. Use a screwdriver to rotate the pot shaft slightly
with respect to the lever. Recheck the point at which the
resistance starts to increase and continue making adjustments
until the increase occurs at 3 mm (1/8") [at 1.5 mm (1/16") for
potboxes without the microswitch]. When adjustment is cor-
rect, tighten the screw holding the lever on the pot shaft, then
recheck to see that this action did not disturb the adjustment.
Make sure that the lever is still seated down on the pot shaft
below the slight bevel on the end of the shaft.
3. Check the resistance with the lever pushed all the way to the
other stop. It should be between 4500 and 5500 ohms. If it is
outside this range, the potbox is faulty and should be replaced.
4. For potboxes equipped with a microswitch, check for correct
switch operation. Use an ohmmeter, or simply listen for the
slight click the switch makes. It should operate when the lever
is 1.5 mm (1/16") from the return stop. If it does not, adjust by
loosening the two screws holding the slotted microswitch mount-
ing plate to the stop spacers and moving the plate. Recheck the
switch operating point after tightening the screws.
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