ORTEC 420 - Calibration and Adjustment Guide; Malfunction Diagnosis

6-3
6.1.6 Timing in the Unipolar Mode
When switch SI is set in the UNIPOLAR position, the lower level discrimi
nator is forced to fire and reset at essentially the same voltage; thus, the
time of the output pulse will vary directly with the signal amplitude and
fall time of the input pulse. This means that timing in the unipolar mode
con be no better than the fall of the pulse times the proportion of the
dynamic range used.
6.2 Calibration Adjustment
It is assumed for this adjustment that all the steps outlined in Section 6.1 have
been completed. To force the lower lever, i.e., the "E" discriminator, to extrap
olate to zero, on adjustment is provided on the printed circuit board. To perform
this adjustment, set the pulse generator controls as given in Section 6.1.4,
step (3). Set the Model 420 DIFF./INT. switch to the INT. position. Adjust the
pulser to achieve half-triggering with the "E" dial placed at 1000, then, adjust
the pulse height dial of the pulse generator to 100 and set the Model 420 "E"
dial to 100, adjusting the zero potentiometer (R14) to achieve half-triggering.
Other points at lower pulse heights may be checked if desired.
6.3 Troubleshooting Suggestions
In situations where the Model 420 is suspected of malfunction, it is essential to
verify such malfunction in terms of simple pulse generator pulses at the input and
output. For this reason, the Model 420 must be disconnected from its position in
any system, and routine diagnostic analysis performed with a test pulse generator
and oscilloscope. It is imperative that testing not be performed with a source and
detector until the amplifier and single channel analyzer system perform satisfac
torily with a test pulse generator. The testing instructions in Section 6.1 of this
manual and the circuit descriptions in Section 5 should provide assistance in
locating the region of trouble and repairing the malfunction. The guide plate and
shield cover may be completely removed from the module to enable oscilloscope
and voltmeter observation with a minimal chance of accidentally short-circuiting
portions of the etched board. The Model 420 may be returned to ORTEC for
repair service at nominal cost; our standardized procedure requires that each
repaired instrument receive the same extensive quality control tests that a new
instrument receives.
6.4 Tabulated Test Point Voltages on Etched Boards
The following voltages are intended to indicate typical dc voltages measured on
the etched circuit board. In some instances the circuit will perform satisfactorily
even though, due to component variations, some voltages measure outside the
given limits; therefore, the voltages given here should not be taken as absolute
values, but rather are intended to serve as an aid in troubleshooting.