Guardian 4389 Diagnostic Repair Manual page 77

SECTION 4.2
OPERATIONAL ANALYSIS
INTRODUCTION
This "Operational Analysis" is intended to
familiarize the service technician with the
operation of the DC control system on
prepackaged units with air-cooled engine. A
thorough understanding of how the system
works is essential to sound and logical
troubleshooting. The DC control system
illustrations on the following pages include a "V-
Type" prepackaged transfer switch.
UTILITY SOURCE VOLTAGE AVAILABLE
See Figure 1, above. The circuit condition with
the AUTO-OFF-MANUAL switch set to AUTO
and with "Utility" source power available can be
briefly described as follows:
"Utility" source voltage is available to transfer
switch terminal lugs N1/N2. With the transfer
switch main contacts at their "Utility" side, this
source voltage is available to terminal lugs
T1/T2 and to the "Load" circuits.
"Utility" voltage is delivered to the primary
winding of a sensing transformer (TX), via
transfer switch wires N1/N2, fuses F1/F2,
connected wiring, and Control Panel "Utility
1/Utility 2" terminals. A resultant voltage
(about 16 volts AC) is induced into the
transformer secondary windings and then
delivered to the circuit board via Wires
224/225. The circuit board uses this reduced
"Utility" voltage as sensing voltage. Wires
224A/225A supply 16 VAC to the battery
charger.
Battery output is delivered to the circuit board
with the AUTO-OFF-MANUAL switch (SW1) set
to AUTO, as shown.
Page 4.2-1
PART 4
Figure 1. Circuit Condition - Utility Source Voltage Available
DC CONTROL