HP 8481A Operating And Service Manual page 10

08481-90049
HP 8481A/82A/83A
board or if the wires have been moved so as to affect the sampling gate
( balance, perform the following procedure:
1. Set the multimeter controls as follows:
FUNCTION dc Voltage
RANGE 20 mV, full scale
2. Set oscilloscope controls as follows:
SENSITIVITY 0.2 V/DIV
SWEEP 1 ms/DIV
TRIGGER INT
DISPLAY A
3. Set the Power Meter CAL FACTOR to 100%. Set the Power Meter
RANGE to 1 mW (0 dBm).
4. Open the Power Sensor (see "Disassembly Procedure' , steps 1
through 3). Zero and calibrate the Power Meter. Leave the opened
Power Sensor connected to the Power Meter POWER REF output.
Heat can affect the adjustments so handle the sensor as little as
possible.
5 xurn OFF the POWER REF switch on the rear panel of the Power
Meter.
6. Remove the HP 435B bottom panel. This will expose the circuit
side of the A5 printed circuit board. On A5 you will see a long
double row of soldered terminals numbered 1 to 44.
7. Connect a probe from pin 40 (the number "902" is printed on the
board next to pin 40) to the multimeter input.
8. Lay the HP 435B on its left side and remove the right panel. This
will expose the A4 assembly.
9. Connect a 1:1 probe from TP4 to channel A on the oscilloscope.
10. Offset. Read the multimeter and adjust the position of the brown
* and white wire until the reading is between -7.0 mV and -2.0 mV.
Helpful hint: the relative position of the brown and white wire to
C4 will adjust the offset.
11. Switching transients. Read the oscilloscope and adjust the position
of the black and white wire until the switching transients are less
than 0.8V peak to peak. Helpful hint: the relative position of the
black and white wire to the collector of Q1 will adjust the switching
transients.
You will find that positioning the wire for switching transients affects
the offset. Go back and forth between the two wires, positioning and
repositioning, until both adjustments are within specifications.