Tektronix 067-0883-99 Instruction Manual page 27

UNIVERSAL LOAD UNIT
CR3002 developes +21 VDC and -21 VDC that are regulated to become the
+12VA and the -12VA output to the DMM Voltage regulator U3004 sets the
base voltage for pass transistor Q3005 to regulate the +12VA supply. The
-12VA supply is regulated by U3005 operating in conjunction with Q3006,
Q3007 and pass transistor Q3008. R3018 is used to adjust the output voltage
for both the +12VA and -12VA supplies.
CR3003 and CR3004 develop a de voltage that is regulated by U3006 to
become the +5VA supply. Neither the +5VA or -5VB supplies have adjustment
potentiometers.
CR3001 developes +21 VDC and -21 VDC that are regulated to become the
-12VB, +5VB and -12VB supplies. Voltage regulator U3003 sets the base
voltage for pass transistor Q3001 to regulate the +12VB supply. The -12VB
supply is regulated by U3003 operating in conjunction with Q3002, Q3003
and pass transistor Q3004. R3005 is used to adjust the +12VB supply. R3010
is used to adjust the -12VB supply.
An adjustment procedure for ULU power supplies is included in Section
4, Calibration.
Power Supply Fuses
The ULU power supply includes five, 1 amp fuses that are accessable
with the side covers removed. Fuse numbers and associated supplies are as
follows:
F3002 protects the
F3003
F3004
F3005
F3006
Exhaust Fans
+12VB and +5VB supplies
-12VB supply
+12VA supply
-5VA supply
-12VA supply
As shown on
schematic~'
AC power to both exhaust fans FM3001 and
FM3002 is via four pins of J8 and through two sets of contacts in K3002.
The rear panel connector P3 SENSE also provides interlock capability for
both fans. When a jumper is installed between P3-16 and P3-34, the current
path for the coil of K3002 is completed to thermal switch S3002. When P3-16
and -34 are not connected, the exhaust fans will run continuously whenever
AC power is applied to the Universal Load Unit. (See note preceding Table
2-3 in Section 2.)
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