Tektronix 1740A Series, User Manual

Page: 174 / 368

Maintenance
1740A/1750A/1760 – Series Service Manual
6–7
Table 6–2: Power Supply Fault Symptoms
Symptom Procedure
Line fuse open Rectifier/Switcher/Snubber Check
Power Supply cycles OFF/ON
Note: Check instrument for shorts. Output Check
Error Amplifier Check
Shutdown Logic Check
Does not power up Controller/Gate Drive Check
Transformer Driver Check
Error Amplifier Check
Shutdown Logic Check
Rectifier/Switcher/Snubber Check
+5 V not regulating Error Amplifier Check
Improper CRT display High Volts Supply Checks
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) +5.0 V
W4 – (+11 V) +10.5 to +12.0 V
W3 – (–11 V) –10.5 to –12.0 V
W2 – (+40 V) +39.0 to +41.0 V
NOTE . The Low Volts power supply troubleshooting is performed without
applying ac power.
b. Disconnect ac power from the instrument. Disconnect the instrument
from the Power Supply by removing the plug jumper from J4.
c. Use the digital multimeter to measure the voltage between TP2 and the
tab (drain) of Q14. Check that the voltage is near 0 V.
Low Volts Supply
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