Maintenance

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.

 

 

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).

b.Connect the negative output of another variable 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 between TP1 and the cathode of CR15.

d.Set the variable DC Power Supply connected to W1 (+5 V) to 4.8 V. The cathode of CR15 should be approximately 20 V.

e.Set the variable DC Power Supply connected to W1 (+5 V) to 5.2 V. The cathode of CR15 should be approximately 2 V.

f.If this check did not reveal the cause for the +5 V supply not regulating, refer to the Output Check and the Control Circuit Check.

High Volts Supply

Table 6-5 lists the High Volts Supply fault symptoms and procedures.

1705A Spectrum Monitor

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Tektronix 1705A instruction manual High Volts Supply