Maintenance

Table 6- 5: High Volts Supply Fault Symptoms

Symptom

Procedure

 

 

Unable to focus crt using the front-

Focus Amplifier Check

panel control

 

 

 

Unable to adjust crt intensity using the

Z--Axis Amplifier Check

front-panel control

Grid Drive Check

 

 

No crt display

High Voltage Oscillator Check

 

CRT Voltage Check

 

 

Load the Low Volts Supply with the instrument, or with the 20Ω resistor as stated at the beginning of the Troubleshooting Procedure.

Focus Amplifier Check

Unsolder and lift one end of R24.

Power up the Power Supply.

Using the digital multimeter, measure the voltage between TP1 and the collector of Q1. It should be approximately -140 V.

Reconnect the lifted end of R24.

Z-Axis Amplifier Check

Unsolder and lift one end of R8.

Power up the Power Supply.

Using the digital multimeter, measure the voltage between TP1 and the collector of Q4. It should be approximately +10 V.

Short together the base and emitter of Q5. The collector of Q4 should be approximately +100 V.

Reconnect the lifted end of R8.

Grid Drive Check

Turn off the Power Supply. Use the digital multimeter’s diode check to test CR1, CR2, CR3, CR5, and CR6 for shorts.

Power up the Power Supply.

Using the digital multimeter, measure the voltage between TP1 and the cathode of CR5. It should vary between approximately +75 and +200 V as R58 (CRT Bias) is adjusted.

6- 16

1705A Spectrum Monitor

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Tektronix 1705A instruction manual Focus Amplifier Check, Axis Amplifier Check, Grid Drive Check