Maintenance
1720/1721
6–11
c. Connect the positive output from the 20 VDC Power Supply to TP1.
Connect the negative output to W3 (–15 V). The circuit should draw
less than 20 mA. Excessive current draw can be caused by CR12.
d. Connect the negative output from the 5 VDC Power Supply to TP1.
Connect the positive output to W1 (+5 V). The circuit should draw less
than 20 mA. Excessive current draw can be caused by CR13 or Q1 and
Q2 (High Volts power supply).
4. Control Circuit Check
a. Connect the negative output from the 20 VDC Power Supply to TP2.
Connect the positive output to the cathode of CR17. Short C47 with a
clip lead. Connect the oscilloscope probe ground to TP2.
b. Table 6–4 lists the signal present in a properly functioning control
circuit.
Table 6–4: Control Circuit Test Points
Circuit Location Signal
U5, pin 1 Approximately 5 VDC
U5, pin 2 Approximately 2 VDC
U5, pin 3 0 V
U5, pin 4 80 kHz triangle wave, 2 V p-p
U5, pin 6 80 kHz square wave, 18 V p-p
U3, pin 1 80 kHz square wave, 5 V p-p
U3, pin 2 2.1 VDC
U3, pin 6 2.9 VDC
U3, pin 7 Approximately 5 VDC
U4, pin 13 80 kHz repetition rate, 300 ns width, approximately 3 V
p-p
Q8, collector 80 kHz repetition rate, 400 ns width, switching from 5 V
to approximately 2 V
c. Remove the clip lead from across C47.
5. Error Amplifier Check
a. Connect the negative output from the variable DC power supply to TP1.
Connect the positive output to W1 (+5 V).
To Next Page
Loading...
Need help?
General
