Maintenance
1705A Spectrum Monitor 6-15
b. Table6--4 lists the signal presentin a properly functioning control
circuit.
Table6- 4: Control Circuit Test Points
CircuitLocation Signal
U5, pin 1 Approximately 5 Vdc
U5, pin 2 Approximately 2 Vdc
U5, pin 3 0V
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, approximat ely 3 V p-p
Q8, collector 80 kHz repetition rate, 400 ns width, switc hing from 5 V to
approximately2 V.
5. Error AmplifierCheck
a. Connect the negative output from the variableDC P owerS upply to TP1.
Connect the positive output to W1(+5 V).
b. Connect the negative output of anothervariable DC Power Supply to
TP1. Connect the positive output to W4 (+15 V). Set the variable
power supply to 20 Vdc.
c. Connect the digital multimeter betweenTP1 and the cathode of CR15.
d. Set the variableDC P owerSupply connected to W1 (+5 V) to 4.8 V.
The cathodeof CR 15 should beapproximately 20 V.
e. Set the variableDC P owerSupply connected to W1 (+5 V) to 5.2 V.
The cathodeof CR 15 should beapproximately 2 V.
f. If this checkdid not reveal the cause for the +5 V supply not regulating,
referto the Output Check and the Control Circuit Check.
Table6--5 lists the High VoltsSupply fault symptoms and procedures.
High VoltsSupply