(2) Battery cleaning. Periodically, or when applicable, clean the exterior
case using mild, non-abrasive cleansers. Do not allow liquids to enter the control
system; a damp cloth will, in most cases, suffice. Disinfectant spraying is
recommended at regular intervals. Clean and dispose of collection-jar systems in
accordance with their respective instructions.
c. Circuit Descriptions.
(1) Ac-to-dc rectifier, power and charging circuits. Refer to figure 2-1.
Components P4, S1A, F1, S2A, D1 through 4, and C1 represent a full-wave-bridge
rectifier circuit which enables simultaneous operation and recharging capability. Lamp
L2 (which is part of S2) indicates the presence of battery charging current which is
limited by R1. Charging current will be higher, initially, when a discharged-battery state
exists, but will taper downward towards the 50-75 mil amp (ma) level as the batteries
replenish. Switch S1A and S1B acts as a master ac/dc power control which, unless
activated, prevents operation from internal or external power sources and battery
recharge. Components D5 and D6 are blocking diodes which prevent false illumination
of L2 during battery operation. Lamp L1, associated with the master-power switch,
illuminates in both internal- and external-power modes via battery power or rectified ac.
Note the S2A and S2B reciprocate which prevents simultaneous operation from internal
and external power. F3 protects the battery pack from high current discharges in
excess of 10a. S8 (model 306M) permits user selection of the input ac source; either
117vac (nominal) or 220-240vac. F4 (model 306M) enables operation from an external
12vdc source whenever the master power switch is activated. Blocking diode D7
isolates the external 12vdc from any other power source. This allows simultaneous
battery recharge from ac power while operating from external 12vdc. Components D1
through 6, C1 and R1 are mounted to heat sink #2 (the flat heat sink), T1 is chassis
mounted, while the other components of this section appear at the front and rear
(2) Suction level and motor speed control circuits. Refer to figure 2-2.
Components F2, L3, S3/R3, R2, S4A, S5A, Q1 through 3, and M1 comprise this
section. Motor M1 is mechanically coupled to a rotary-vane vacuum pump. The
vacuum or airflow generated by this pump is relative to the motor speed driving it.
Therefore, the motor speed-control circuit acts as an electronic vacuum regulator.
Component S3/R3 is a rotary-switch/potentiometer which provides base drive to a two-
stage emitter-follower amplifier, Q1 through Q3.
(a) Increasing the positive potential at the base of Q1 increases the
paralleled outputs of Q2 and Q3 causing M1 to turn faster and generate higher vacuum
and airflow levels. Two vacuum ranges are possible, depending upon the position of
S4A. When S4A is closed, you can apply full power potential to the base of Q1 which
generates maximum vacuum levels (550mmHg). However, if S4A is opened, the
maximum potential available to the base of Q1 is limited by the setting of R2 and can
only provide a maximum pump output level of 200mmHg when properly calibrated.
Switch S5A, when closed, provides a direct input to the base of Q1.