Tektronix WFM601, Service Manual, Page: 140 / 304

Maintenance
6–8
WFM 601 - Service Manual
Table 6–2: Power Supply Fault Symptoms (Cont.)
Symptom Procedure
+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 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.
CAUTION.
Do not proceed until the drain of Q14 is near 0 V. Dangerous voltage
potentials are present in the circuit until the capacitors discharge.
2. Rectifier/Switcher/Snubber Check
a. Use the digital multimeter to measure the voltage between TP2 and TP3.
Be sure the voltage is near 0 V before proceeding.
b. Remove jumper P7.
Low Volts Supply