Tektronix WFM 601A, Service Manual

Page: 149 / 368

Maintenance
WFM 601A, WFM 601E, & WFM 601M Service Manual
6–29
3. Output Check (Supply Secondary)
a. Connect the negative output from the 20 V
DC
Power Supply to TP1 and
its positive output to W3 (+11 V). The circuit should draw less than
20 mA. Excessive current draw may indicate a fault in CR16 or U2
(High Volts Power Supply).
NOTE
. The variable power supply used in the following checks must have a
current limit of 1 ampere or less.
b. Connect the negative output from the 20 V
DC
Power Supply to TP1 and
the positive output to R69 (+40 V). The circuit should draw less than
20 mA. Excessive current draw may indicate a fault in CR19 or Q7
(High Volts Power Supply).
c. Connect the positive output from the 20 V
DC
Power Supply to TP1and
the negative output to W2 (–11 V). The circuit should draw less than
20 mA. Excessive current draw may indicate a fault in CR18.
d. Connect the negative output from the 5 V
DC
Power Supply to TP1 and
the positive output to TP4 (+5 V). The circuit should draw less than
20 mA. Excessive current draw may indicate a fault in CR17 or Q11 and
VR1 in the High Volts section of the Power Supply.
4. Controller/Gate Drive Check
a. Remove jumper P6.
b. C20 V
DC
to the left end of R122 or R120 and connect the
common lead to TP3.
c. Short together pins 1 and 2 of U6.
d. Table 6–5 shows the signals present when the control circuit functions
properly.
Table 6–5: Control circuit test points
Circuit location Signal
U6, pin 3 0 V
U6, pin 4 sawtooth wave, 2 V p-p, 200 kHz
U6, pin 6 80 kHz square wave, 18 V p-p, 100 kHz