Manitowoc Published 10-01-2012, Control # 045-08 1-51
777 SERVICE MANUAL INTRODUCTION
1
The PC also energizes front drum park brake solenoid HS12
and front drum band brake solenoid HS16. As the solenoid
shift, hydraulic system pressure is supplied to release the
front drum hydraulic park brakes. The brakes then release,
permitting the front hoist motor to rotate the front drum in the
lowering direction, opening the bucket.
Lower Bucket
See Figure 1-35 for following procedures.
When rear hoist control handle is pushed forward, the PC
energizes front and rear drum park brake solenoids HS12,
HS8, and front and rear drum band brake solenoids HS16,
and HS17. As the solenoids shift, hydraulic system pressure
is supplied to release the front and rear drum hydraulic park
brakes.
At the same time, the PC closes reverse regulated polarity
voltage circuits to the front and rear hoist pump EDCs. The
EDCs tilt the pump swashplates in the lowering direction,
causing the front and rear hoist motors to rotate the drums
and lower the bucket. The PC maintains equal linepull on the
drums by monitoring the speed data received from front and
rear drum speed senders and making the necessary
adjustments. The PC also governs the lowering speed by
varying the current to the front and rear hoist pump EDCs in
conjunction with movement of rear hoist control handle.
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