Steris Amsco 3085 SP, Maintenance Manual

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The hand-control PC board is powered by +5 Vdc from
the dc-dc converter on the table-control PC board.
3.4.2.5 Override Switch Control Board
All signals generated by the override switches are
controlled by this board, i.e., all table-positioning and
floor-lock switch signals. The hand control, table-control
PC board and most circuitry on the power-control PC
board are bypassed when any override switch is
engerized. A 24-Vdc power supply, either from the
batteries or from the line cord, is necessary to operate the
hydraulic solenoid coils. It is not needed for the hydraulic
pump since a foot operated pump backs up this device.
When an override switch is energized, four multi-poled
relays (CR1, CR2, CR3 and CR4) are energized, isolating
the hydraulic solenoid coils from the tablecontrol PC
board and the hand control. Simultaneously, a dc ground
signal is fed to the power-control PC board to turn on the
hydraulic pump if possible (see note), and to turn off
power to the hand control.
NOTE: If the line cord is plugged into the table or if
motor-battery power is available (battery powered
tables only), the hydraulic pump will come on.
Otherwise, the control batteries are used along with
the manual pump. The control batteries do not have
the capability to run the hydraulic pump.
The second pole of the override switch applies a dc
ground to the proper hydraulic coil for activation.
Circuitry on the board prevents more than one switch
being acknowledged.
A Resistive-Capacitive (RC) circuit exists on the CR3 and
CR4 relay coils to time-delay-off these two relay coils if
an override articulation has been selected. This is