Instruction manual

Maintenance
1720/1721
6-9
determining which section of the power supply the problem is in. Apply ac
power and turn on the power supply. From Table 6--2, determine which
symptom the power supply exhibits and refer to the corresponding procedure.
Table 6- 2: Power Supply Fault Symptoms
Symptom Procedure
Line fuse open Rectifier/Switcher Check (Low Volts)
Power Supply cycles OFF/ON Output Check (Low Volts), or
High Voltage Oscillator Check (High Volts)
Does not power up Control Circuit Check (Low Volts)
+5 V not regulating Error Amplifier Check (Low Volts)
Improper CRT display High Volts Supply
NOTE. Low Volts Supply Load:
A20Ω, 2 watt resistor should be used as a load for the Low Volts Supply.
Disconnect J4 and connect the 20Ω resistor between W1 (+5 V) and TP1
(secondary ground).
1. Preliminary Checks
a. A properly functioning and loaded Low Volts supply will output the
voltages listed in Table 6--3. Use the DMM to measure the voltages
between TP1 and the voltage test points. If the supply is not regulating
properly, continue with the procedure.
Table 6- 3: Low Volts Supply Voltages
Test Point Voltage Range
W1 -- (+5 V) +4.88to+5.12V
W4 -- (+15 V) +14.0 to +16.0 V
W3 -- (--15 V) --14.0 to --16.0 V
W2 -- (+40 V) +39.0 to +41.0 V
Low Volts Supply