Specifications

Calibration and Repair
61
CALIBRATION AND REPAIR
Most of the calibration parameters are determined
by a computer aided calibration procedure after
burn-in at the factory. These calibration
parameters are stored in the permanent memory of
each unit.
This section details the calibration of the signal
inputs which, because of their high speed, require
some hand adjustment. In addition, the repair
procedure for the signal inputs is discussed.
**** WARNING ****
The calibration procedure requires adjusting the
instrument with power applied and so there is a
risk of personal injury or death by electric shock.
Do not remove the covers from the shielded power
supply when the power is on!
Please be careful.
SIGNAL INPUT OFFSET
To calibrate the input offset, connect a voltmeter
to a signal input. P101 adjusts INPUT 1 and P121
adjusts INPUT 2. These potentiometers are located
behind the signal inputs. Adjust the correct
potentiometer for a reading of 0 ± .1 mV on the
meter.
SIGNAL INPUT REPAIR
The diodes in the overload protection circuit can
be damaged by excessive voltages at the inputs.
To check for damage, measure for 0.6 V across
both diodes in D101 and D121. D102, D103,
D122, and D123 can be tested by removing them
from the circuit and then checking for degradation
of the amplifiers pulse response as each diode is
reconnected. The amplifier outputs can be viewed
with a fast oscilloscope across R201 and R212.
Replacement diodes are available from the factory.
Performing these adjustements or replacements
can result in the discriminator levels being slightly
miscalibrated. The discriminator offsets may be a
few mV larger after repair or adjustement.