ORTEC 420 User manual

INSTRUCTION MANUAL
MODEL 420
TIMING SINGLE CHANNEL ANALYZER
Serial No.
Purchaser.
Date Issued
OAK RIDGE TECHNICAL ENTERPRISES CORPORATION
p. O. BOX C
OAK RIDGE, TENNESSEE
Telephone [phone]
TWX 810-572-1078
) Osk Ridge Technical Enterprises Corporation 1966
Printed In U.S.A.

TABLE OF CONTENTS
Page
WARRANTY
PHOTOGRAPH
FORWARD: Introduction To Fast Timing With Linear Signals
1 . DESCRIPTION 1-1
2. SPECIFICATIONS 2-1
3. INSTALLATION INSTRUCTIONS 3-1
3.1 General 3-1
3.2 Connection To Power - Nuclear Standard Bin, ORTEC Model 3-1
401/402
3.3 Connection To A Linear Amplifier 3-1
3.4 Linear Output Signal Connections And Terminating Impedance 3-2
Considerations
4. OPERATING INSTRUCTIONS 4-1
4.1 Front Panel Control Functions 4-1
4.2 Initial Testing And Observation Of Waveforms 4-2
4.3 Connector Data 4-3
4.4 Typical Operating Conditions 4-3
5. CIRCUIT DESCRIPTION 5-1
6. MAINTENANCE INSTRUCTIONS 6-1
6.1 Testing Performance 6-1
6.2 Calibration Adjustment 6-3
6.3 Troubleshooting Suggestions 6-3
6.4 Tabulated Test Point Voltages on Etched Boards 6-3

STANDARD WARRANTY FOR ORTEC ELECTRONIC INSTRUMENTS
DAMAGE IN TRANSIT
Shipments should be examined immediately upon receipt for evidence of external or con
cealed damage. The carrier making delivery should be notified immediately of any such damage,
since the carrier is normally liable for damage in shipment. Packing materials, waybills, and other
such documentation should be preserved in order to establish claims. After such notification to the
carrier, notify ORTEC of the circumstances so that we may assist in damage claims and in providing
replacement equipment when necessary.
WARRANTY
ORTEC warrants its electronic products to be free from defects in workmanship and materials,
other than vacuum tubes and semiconductors, for a period of twelve months from date of ship
ment, provided that the equipment has been used in a proper manner and not subjected to abuse.
Repairs or replacement, at ORTEC option, will be made without charge at the ORTEC factory.
Shipping expense will be to the account of the customer except in cases of defects discovered upon
initial operation. Warranties of vacuum tubes and semiconductors, as made by their manufacturers,
will be extended to our customers only to the extent of the manufacturers' liability to ORTEC.
Specially selected vacuum tubes or semiconductors cannot be warranted. ORTEC reserves the right
to modify the design of its products without incurring responsibility for modification of previously
manufactured units. Since instal lation conditions are beyond our control, ORTEC does not assume
any risks or liabilities associated with the methods of installation, or installation results.
QUALITY CONTROL
Before being approved for shipment, each ORTEC instrument must pass a stringent set of
quality control tests designed to expose any flaws in materials or workmanship. Permanent records
of these tests are maintained for use in warranty repair and as a source of statistical information
for design improvements.
REPAIR SERVICE
ORTEC instruments not in warranty may be returned to the factory for repairs or checkout at
modest expense to the customer. Standard procedure requires that returned instruments pass the
same quality control tests as those used for new production instruments. Please contact the factory
for instructions before shipping equipment.

I
'4^
ortec*
MODEL 420
TIMING
SINGLE CHANNEL
ANALYZER
"E"
DISC
0-1
DELAY
DIFF. WALK BIPOLAR
4: -0,
INT.
Adj. UNIPOLAR
■■
NEG.
INPUT
IT n
POS.
OUTPUT
Model 420 Timing Single Channel Analyzer

MODEL 420
TIMING SINGLE CHANNEL ANALYZER
Foreword
Introduction to Fast Timing With Linear Signals
Precise determination of the time of occurrence of nuclear events is often compli
cated. Detection of these events usually results in a voltage pulse whose amplitude
is a function of the energy loss in the detector, and whose rise time is a function of
the conversion process from detector energy to charge. When time determination is
derived from the leading edge of such a pulse (by means of a discriminator, e.g., a
Schmitt trigger), there is a time shift of the discriminator output that depends on the
pulse rise time and the range of pulse amplitudes involved. (See Figure 1(a).) The
rise time of these pulses is usual ly limited by the linear amplifier which is necessary
for pulse height analysis; such amplifiers are the Models 410, and the older versions
OS the Model 203, A-8 and DD2, etc. For those amplifiers which have variable RC
shaping, e.g., the Model 410, the rise time and fall time will vary directly with
the integration and differentiation time constants chosen; therefore, the zero crossing
time will vary in real time. The time of zero crossing in real time is approximately
2 time constants after the detector event when the double RC differentiation is used.
Figure 1(b) shows a series of idealized output pulses from a double delay line clipped
amplifier, superimposed upon each other. All of the pulses pass through the baseline
at the same time; this is true because in the amplifier clipping process, the voltage
which is forming the pulse shape goes from a positive value (+E) to on equal negative
value (—E) in the same time that wasrequired forthe voltage to go from 0 to +E, i.e.,
one rise time. The pulses, therefore, pass through the baseline (zero volts)at a time
Tr r
-01 DISC. TRIGGER LEVEL
Tr/i
— DISC. TRIGGER LEVEL
DISC. \i,
OUTPUTS h J
TIME SHIFT WITH LEADING EDGE TRIGGER
(6)
TIME SHIFT WITH CROSSOVER PICKOFF
Figure 1. Timing From Linear Amplifier Output Pulses

t
1-1
corresponding to 1/2, but displaced along the time axis by the one clipping time,'".
Thus, it is evident that the time 1/2 corresponds to the point at which the pulses attain
half-height. Since in linear amplifiers the rise time is constant and therefore inde
pendent of pulse height, the time at which the pulses reach half-height is also con
stant and independent of pulse height. The discriminator in the Model 420 is designed to
trigger on the leading edge of the pulse, at a selected voltage, and is forced to reset
when the pulse passes through zero volts. The discriminator output pulse is then differ
entiated, and the reset edge is used to furnish an output pulse that is relatively jitter-free
for timing. Time resolution in the order of 5 to 10 nanoseconds independent of discrimi
nator level is typical for this circuit.
1. DESCRIPTION
The Model 420 Timing Single Channel Analyzer, as indicated by its title, performs two
functions. First, it is a single channel analyzer, with,both the lower level and the window
width variable over the pulse height range. For input signals which are doubly differ
entiated, it furnishes an output which occurs at the time these signals go through zero.
This time, as explained in the preceding introduction, is a precisely known time and there
fore the output time from the Model 420 is a precise time. The unit will accept single or
double delay line differentiated signals or single or double RC differentiated signals with
pulse widths from 200 nanoseconds to 20 microseconds. When the unit is fed a unipolar
pulse, the crossover time is not fixed in time and therefore the input selector switch should
be set to the unipolar position. This will cause the discriminator to reset at the same pulse
height at which it was triggered, and therefore the time of output pulse will depend upon
the fall time of the signal input. The unit is provided with a variable delay, selectable by
a front panel control, of approximately 1000 nanoseconds to allow time balance in
coincidence circuitry and analyzer gating. The unit provides two outputs whose leading
edges contain the same timing information. One is a negative spike used for very fast
timing such as time to pulse height converters, etc., and the other is a positive 5-volt,
500-nanosecond-wide pulse for slower applications such as coincidence circuits and
analyzer gating. These output pulses are the two standard forms of logic pulses in the
ORTEC 400 Series modular instruments, and are compatible with all related input signal
requirements.

2-1
2. SPECIFICATIONS
INPUT SIGNAL REQUIREMENTS:
Amplitude Range 100 mV to 10 V
Pulse Width Range 200 nsec to 20 (xsec
Polarity Positive (Unipolar) or Positive Portion leading (Bipolar)
CONTROLS:
Lower Level ("E") 100 mV to 10 V, 10-turn control
Window Width ("AE") 100 mV to 10 V, 10-turn control
Delay 0 to 1000 nsec, 10-turn control
DiflFerentiol-integrol Mode Switch, integral position disables "AE" Discriminator
Unipolar-Bipolar Mode Switch
LINEARITY (as percent of full span):
"E" <±0.25%
"AE" <±0.25%
Delay < ± 2 %
TEMPERATURE STABILITY (as percent of full span):
"E" ." .. .< ± 0.015%/C°
"AE" <±0.015%/C°
Delay < ± 0.4 nsec/C°
TIME SHIFT VS. PULSE HEIGHT* < ±2 nsec for a factor of (XI0) or ± 10 nsec for
(X50) *Specified withiORTEC Model 410 Amplifier,
Double-Delay-Line Mode, Integrate 0.2 /xsec
OUTPUT SIGNALS Both occur simultaneously and may be delayed 0 to
1.0 /xsec by means of a 10-turn DELAY control
Fast Negative, 0.6 V (min), T,. < 5 nsec. Width < 20 nsec
Slow Positive, 5 V, Tr < 20 nsec. Width ~ 500 nsec
POWER REQUIRED 30 mA at + 24 V, 30 mA at — 24 V
50 mA at + 1 2 V, 40 mA at —1 2 V
WEIGHT ~ 2.5 pounds net
SIZE Standard double width module (2.70 inches wide) per
TID-20893
_J

3-1
3. INSTALLATION INSTRUCTIONS
3.1 General
Model 420, used in conjunction with Model 401/402 Bin and Power Supply, is
intended for rock mounting, and therefore it is necessary to ensure that vacuum
tube equipment operating in the some rock has sufficient cooling air circulating
to prevent any localized heating of the all-transistor circuitry used throughout the
Model 420. The temperature of equipment mounted in racks can easily exceed
the recommended maximum unless precautions are taken; Model 420 should not
be subjected to temperatures in excess of 120''F (50° C).
^ 3.2 Connecton to Power—Nuclear Standard.Bin, ORTEC Model 401/402
Model 420 contains no internal power supply, and therefore must obtain power
f from a Nuclear Standard Bin and Power Supply such as ORTEC Model 401/402.
I It is recommended that the Bin power supply be turned off when inserting or
' removing modules. The ORTEC 400 Series is designed so that it is not possible
to overload the Bin power supply with a full complement of modules in the Bin;
however, this may not be true when the Bin contains modules other than those of
ORTEC design. In this case, power supply voltages should be checked after the
' insertion of modules. Model 401 /402 has test points on the power supply control
panel to monitor the dc voltages.
3.3 Connection to a Linear Amplifier
The input to the Model 420 is via a front panel BNC connector and is compatible
with all linear amplifiers capable of producing 10-volt unipolar or bipolar output
signals onto a 2000-ohm load, with the positive excursion of a bipolar signal
leading the negative excursion in real time. The input operating range is from
threshold, typically 100 millivolts, to 10 volts, This unit may be used with vacuum
tube amplifiers which are capable of output signals of 100 volts, if the output
signal from the amplifier is attentuated so that it cannot exceed 10 volts. Simple
resistive attenuators installed in the vacuum tube amplifiers will make them com
patible with related transistor equipment.

3-2
3.4 Linear Output Signal Connections and Terminating impedance Considerations
The source impedance of the 0-10 volt standard linear outputs of most 400
Series modules is approximately 1 ohm. Interconnection of linear signals
is, thus, non-critical since the input impedance of circuits to be driven is
not important in determining the actual signal span, e.g., 0-10 volts, de
livered to the fol lowing circuit. Paralleling several loads on a single out
put is therefore permissible while preserving the 0-10 volt signal span.
Short lengths of interconnecting coaxial cable (up to approximately 4 feet)
need not be terminated. However, if a cable longer than approximately
4 feet is necessary on a linear output, it should be terminated in a resistive
load equal to the cable impedance. Since the output impedance is not
purely resistive, and is slightly different for each individual module, when
a certain given length of coaxial cable is connected and is not terminated
in the characteristic impedance of the cable, oscil lations wil l generally
be observed. These oscillations can be suppressed for any length of cable
by properly terminating the cable either in series at the sending end or in
shunt at the receiving end of the line. To properly terminate the cable
at the receiving end, it maybe necessary to consider the input impedance
of the driven circuit, choosing on additional paral lel resistor to make the
combination produce the desired termination resistance. Series terminating
the cable at the sending end may be preferable in some coses where re
ceiving and terminating is notdesirable or possible. When series terminat
ing at the sending end, ful l signal span, i.e., amplitude, isobtainedat
the receiving end only when it is essential ly unloaded or loaded with an
impedance many times that of the cable. This may be accomplished by
inserting a series resistor equal to the characteristic impedance of the ca
ble internally in the module between the actual ampiifier output on the
etched board and the output connector. It must be remembered that this
impedance is in series with the input impedance of the load being driven,
and in the case where the driven load is 900 ohms, a decrease in the signal
span of approximately 10% will occur for a 93-ohm transmission line. A
more serious loss occurs when the driven load is 93ohms and the transmis
sion system is 93 ohms. In this case, a50% loss will occur. BNC connec
tors with internal terminators are available from a number of connector
manufacturers in nominal values of 50, 100, and lOOOohms. ORTEC stocks
in limited quantity both the 50 and 100 ohm BNC terminators. The BNC
terminators are quite convenient to use in conjunction with a BNC tee.

4-1
4. OPERATING INSTRUCTIONS
4.1 Front Panel Control Functions
"E" DISC.
The function of the "E" (or energy) discriminator is the some as with any discrimi
nator, i.e., to prevent discriminator triggering by those signals which are below
the selected threshold. The threshold range of this discriminator is from approxi
mately 100 millivolts to 10 volts direct reading on the dial.
"AE" DISC.
The "AE" discriminator forms the upper level of the single channel analyzer. The
dial of this discriminator reads the difference in voltage or energy between the
"E" discriminator and the upper level; therefore, it reads "AE." Since this forms
the upper level of the single channel analyzer, the output from this discriminator
is placed in anticoincidence with an output from the lower level or "E" discrimi
nator so that when triggered, there is no output. Therefore, to obtain an output
from this unit a signal must be bigger than the "E" setting but less than "E"
+ "AE." (When the Differential/Integral (DIFF./INT.) switch is set to the INT
position, the "AE" function is disabled, and the unit becomes an integral dis
criminator which is controlled by the "E" dial.)
Delay Control
When the bipolar signal passes from a positive to a negative value, or when the
unipolar signal recrosses the "E" discriminator setting (depending upon the selec
tion of unipolar or bipolar operation by means of switch SI), a logic signal to be
used for timing or counting operation is generated. The delay control allows the
output logic signal to be delayed in time from this reference time, to+ a constant
propagation delay, over a range of 0 to 1000 nanoseconds. This delay is con
tinuously variable by means of a 10-turn potentiometer.
UNIPOLAR/BIPOLAR Switch (SI)
Switch SI selects the mode of operation of the timing unit, and should be set to
correspond to unipolar or bipolar signals at the input; i.e., if the input signal is
a singly differentiated pulse this switch should be in the UNIPOLAR position, and
if the input signal is a bipolar signal the switch should be in the BIPOLAR posi
tion. Precise timing is available only when the signal is a bipolar signal.

4-2
DIFF./INT. Switch (32)
Switch 52 determines whether the unit shall be on integral timing discriminator or
o timing single channel analyzer. When this switch is in the DIFF. position all
signals which trigger the AE discriminator will prevent the logic signal created by
the timing discriminator from reaching the output, and therefore there will be no
output from the unit. When the switch is in the INT. position, the AE discriminator
is disabled, and all signals which exceed the lower level threshold will create an
output signal.
WALK Adj.
Due to minor circuit differences, various amplifiers will have a true crossover at
different values of voltage, but very near zero. For this reason, a WALK adjust
ment is provided on the front panel. This is a screwdriver adjustment and is
adjusted to an optimum value with a Model 410 Amplifier before the unit leaves
the factory. For information concerning the method of adjustment, refer to "Cali
bration Adjustment," Section 6.1 of this manual.
4.2 Initial Testing and Observation of Waveforms
Refer to Section 6.1 for information on testing performance and observing wave
forms.
4.3 Connector Data
CN1 — INPUT (BNC) Connector
CN1 has input impedance of 2000 ohms, oc-coupled, and a maximum input of
10 volts. To minimize reflections when driving into CNl from a low impedance
voltage source such as the output of the Model 410, etc., CNl should be extern
ally terminated in the characteristic impedance of the connecting coaxial cable.
CN2—OUTPUT NEG. (BNC) Connector
Output driving source impedance is less than 10 ohms. The signal is dc coupled
starting from zero volts; it is the standard ORTEC Fast Negative logic signal and
is used for optimum timing resolution.
CN3 —OUTPUT POS. (BNC) Connector
Output driving impedance is less than 10 ohms. The signal is dc coupled starting
from zero volts; it is the standard ORTEC positive logic pulse whose application
is normally coincidence timing and analyzer gating.
OUTPUT Test Points
Oscilloscope test points for monitoring output signals are available at each
OUTPUT BNC. Each test point has a 470-ohm series resistor connecting it to the
respective OUTPUT BNC connector.

4-3
4.4 Typical Operating Conditions
The realization of both optimum timing and optimum energy resolution are mutu
ally exclusive when using the crossover pickofF method of timing; however, a
satisfactory compromise of timing and resolution is usually not difficult to obtain.
Optimum timing is realized with wide bandwidth capabilities in the linear ampli
fier, resulting in fast rise and fall times. Optimum energy resolution is realized
with narrow bandwidth so that the bypass of the noise spectrum can be selectively
chosen at a particular location in the frequency spectrum.
The method of compromise is illustrated with reference to the model 410
Amplifier when used in conjunction with the Model 420 Timing Single
Channel Analyzer. To optimize timing, the Model 410 would be operated: 1) with
a minimum of integration and double delay line differentiation; or 2) in the double
RC shaping mode with the integration and differentiation time constants set on
0.1 microsecond. The optimization of timing would be at the expense of energy
resolution. If it is desired to optimize the energy resolution, the Model 410 should
be operated: 1) with an integration time constant of 1 or 2 microseconds and
double delay line differentiation; or 2) in the double RC shaping mode with the
integration and differentiation time constants set at 1 or 2 microseconds. In the
latter case, it is observed that the rate of change of voltage when the linear
amplifier output crosses through zero is very much less than in the former case.
With the lower rote of change, the noise modulation of the linear amplifier output
signal causes a larger time jitter of the timing output signal. In the former cose,
the rote of change of voltage with respect to time is quite high and the jitter in
the timing output due to linear amplifier noise modulation is quite small.
Jj^

5-1
5. CIRCUIT DESCRIPTION (See Drawings 420-0001-SI and 420-0002A-B1.)
Resistors R1 and R5 form a resistive voltage divider v/hich divides the input signal from
a maximum of 10 volts to a maximum of 5 volts at the base of Q1 and Q9. Q1 and Q2
form a long-tail pair which is the lower level discriminator. Transistors Q3 through Q8
are necessary to obtain the control desired on the hysteresis of the circuit. Q3 and Q5
are normally on in the absence of an input signal and hold the base of Q2 at zero volts.
When on input signal exceeds the threshold level set by the "E" discriminator, R2, the
trigger pair, Q1 and Q2, regenerates and triggers another trigger pair formed of Q7 and
Q8. Q7 turns on and Q8 turns off. When Q8 turns off, this allows the emitter of Q4 to
fall toward —12 volts and it is caught at —E. When the emitter of Q4 and base of Q6 fall
negative, Q6 turns on and Q5 turns off, which sets the base of Q2 at —E. Since the base
of Q1 has a baseline voltage equal to —E and the base of Q2 has a baseline voltage of
-E in the presence of the signal, the trigger pair will reset when the signal makes the
transition from the positive condition to the negative condition, i.e., zero crossing point.
The signal at the collector of Q7 is differentiated by means of L3 and is fed to the base
of Q15. The negative portion of the signal will cause Q15 to conduct if the upper level
discriminator has not been triggered. A signal from the collector of Q6 is used to reset
the upper discriminator when it has been triggered, and this signal is fed to the base of
Q11. R14, the zero adjust trimpot, is used to zero the "E" pulse height dial. The adjust
ment of the walk adjust potentiometer, R6, will be explained in Section 6.1. Switch SI is
used to obtain operation in either bipolar or unipolar mode. In the bipolar position, tran
sistor Q4 has the value of —E imposed on its base at all times; however, in the unipolar
position this base sees a constant —75 mV dc voltage. This dc voltage is the amount of
hysteresis on the lower level discriminator in the unipolar mode.
The upper level discriminator is formed by Q9 and QIO. The output from QIO is
differentiated and fed to the base of Q12. When switch S2 is in the differential position,
this signal is sufficiently large to trigger the multivibrator composed of Q12 and Q13.
If, however, 52 is in the integral mode, this pulse cannot trigger the multivibrator com
posed of Q12 and Q13. Once this multivibrator is triggered, it could recover with an RC
recovery time of approximately 100 microseconds; however, it is reset at essentially zero
crossing time by means of the reset pulse which is present by way of Q11. Due to the
long time constant involved with this multivibrator, this circuit con handle pulse widths
which are very wide, e.g., 20 microseconds.
An output from Q13 will cause Q14 to inhibit any signal that appears at the base
of Q15; thus, the anticoincidence function is performed between the "AE" discriminator
and the "E" discriminator. This anticoincidence function assures that the input pulsie must
be within the selected window to obtain an output. Q16,Q17,Q18, and Q19 form a
delay generator. The delay control, R46, will vary the delay of the output logic signal

5-2
over a range of approximately 1000 nanoseconds. This delay should be quite linear.
The delay generator triggers with an input pulse from Q15 and then resets when the
signal at the base of Q17 recovers to the zero voltage level. The recovery time constant
is set by capacitor C19 and the constant current generator, Q19. The pulse from the col
lector of Q17 is differentiated and the negative portion is fed out through Q20 as a fast
output signal. An inversion of this some signal appears at the collector of Q20 and
triggers the multivibrator composed of Q21 and Q22. The signal from the collector of
Q22 is emitter-follower buffered to the output as a positive 5-volt signal, 0.5 micro
second wide.
( '■

6-1
6. MAINTENANCE INSTRUCTONS
6.1 Testing Performance
6.1.1 Introduction
The following paragraphs are intended as an aid in the installation and
checkout of the Model 420. These instructions present information on front
panel controls, waveforms and test points, and output connectors.
6.1.2 Test Equipment
The following or equivalent test equipment is needed:
(1) ORTEC Model 419 Pulse Generator
(2) Tektronix Model 545 Series Oscilloscope
(3) 100-ohm BNC terminators
(4) ORTEC Model 410 Amplifier
(5) Schematics and Block Diagrams for the Model 420 Timing Single
Channel Analyzer
6.1.3 Preliminary Procedures
(1) Visually check module for possible damage due to shipment.
(2) Connect ac power to Nuclear Standard Bin, e.g., ORTEC Model
401/402.
(3) Plug module into Bin and check for proper mechanical alignment.
(4) Switch on ac power and check the dc power voltages at the test points
on the Model 401 Power Supply control panel.
t r
6.1.4 Testing the Single Channel Function
(1) Connect the direct output of the pulse generator to the scope trigger.
Connect the attenuated output of the pulse generator to the input of
the Model 410 Amplifier. Place all attenuator switches on the pulse
I generator to the out position except one switch, which should be an
XI0 switch. Set the Model 410 Amplifier DIFFERENTIATION control to
double delay line. Set the INTEGRATION control to the .1 fisec posi-
i tion. Adjust the pulse generator output and/or amplifier gain control
to achieve an amplifier output pulse height of approximately 10 volts.
< ] (2) Connect the amplifier output to the single channel analyzer input. Set
the Model 420 DIFF./INT. switch to the INT. position, and set the
BIPOLAR/UNIPOLAR switch to the BIPOLAR position. Adjust the "AE"
dial to read 500/1000 divisions. There should now be on output from
both fast and slow outputs of the single channel analyzer. Turn the
I "E" dial to read 1000, then adjust the pulse height dial on the pulse

6-2
generator so that the single channel half-triggers. Now set the X2
attenuator switch on the pulse generator. The single channel should
again half-trigger at 500 dial divisions. Next, set the DIFF./INT. switch
to the DIFF. position, and turn the "E" dial to 400 divisions. Turn the
"AE" dial toward zero and observe when the single channel again
begins to half-trigger. This should be approximately 100 dial divisions
on the "AE" dial. We are now certain that the single channel analyzer
is operating as a single channel in the bipolar mode. These same steps
may be repeated for the unipolar mode if desired, and other points
on the pulse height vs dial curves may be observed.
6.1.5 Testing the Timing Function
(1) It is assumed for this test that the steps in 6.1.4 have been performed
and that switch SI is in the BIPOLAR position. Connect the direct output
of the pulse generator to the trigger input to the "B" sweep on the
scope and set the scope for "A" triggered by "B." Obtain such trig
gering of the "A" sweep that the delay control in the "B" sweep
section may be used.
(2) Turn the DELAY control on the Model 420 to 0 and observe the output
pulse either at TP1 or at TP2, then adjust the scope sweep speed and
"B" sweep delay to observe the leading edge of this pulse with a
sweep speed of 20 nanoseconds/cm or less. Set the DIFF./INT. switch
to the INT. position on the Model 420. Set the pulse generator switches
as described in Section 6.1.4, step (4). Place the "E" discriminator at
10 divisions. Attenuate the pulse height by factors of 2, 5, and 10 by
means of the attenuator switches on the pulse generator, and observe
the time shift of the output pulse; the time shift should be less than
4 nanoseconds over this pulse height range. It may be necessary to
trim the time shift by means of the WALK Adj. screwdriver adjustment
(R69) on the front panel. For those users who have critical dynamic
range problems, the single channel may be checked and adjusted to
achieve less than ±10 nanoseconds time shift over a dynamic range
of 50:1, i.e., from 200 mV to 10 volts. Operation with this wide a range
becomes quite critical and R69 may have to be slightly readjusted to
achieve this characteristic. Of course, at very low pulse heights the
amount of jitter observed will be large; this is due to the amplifier
noise modulation of the crossover point.
(3) Set the scope sweep speed at 50 nanoseconds/cm. Observe the out
put signal and turn the DELAY control (R46) through its range. The
output should shift approximately 1000 nanoseconds.

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.

6-4
Table 6.1 Typical DC Voltages
NOTES: ]. All voltages ore measured from ground with vtvm having Impedance of 10 megohms or greater.
2. All voltages ore dc values with no input signals.
3. Set all dials to read ICQ divisions.
4. Set DIFF./INT. switch to DIFF., and BIPOLAR/UNIPOLAR switch to BIPOLAR.
Pin No.
Location
Minimum
Maximum
A
+ 24 bus + 23.6
+ 24.0
B + 1 2 bus
+ 11.5
+ 12.0
C
- 12 bus
- 11.5
— 12.0
D — 24 bus
— 23.6
— 24.0
E Junction of R2 & R3
— 4.9
-5.1
F
Junction of R30 & R31
+ 4.9
+ 5.1
G
Ql-C
+ 11.4
+ 11.9
H
Q4-E
MM 7^/4 0
mm V
1
Junction of R21 & R22
-0.060 -0.080
J Q9-C + 11.3 + 11.8
K
Q12-C
+ 11.3 + 11.8
L
Q15-C
0 0
M Q16-C
+ 11.3 + 11.8
N
Q19-B
+ 1 7.2
+ 18.2
O
Q21-C
0 0
P
Q22-C
+ 0.37
+ 0.50
Q
Q23-E
0 0
C — Collector
B — Base
E — Emitter

BIN/MODULE CONNECTOR PIN ASSIGNMENTS
FOR AEC STANDARD NUCLEAR INSTRUMENT MODULES
PER TID-20893
Pin Function
Pin Function
1
+3 volts
23
Reserved
2
—3 volts
24 Reserved
3
Spare Bus
25
Reserved
4
Reserved Bus
26
Spare
5
Coaxial 27
Spare
6
Coaxial
*28
+24 volts
7
Coaxial
*29
—24 volts
8
200 volts dc
30 Spare Bus
9
Spore
31
Carry No. 2
♦ 10
+6 volts
32
Spare
*11
—6 volts
*33
115 volts acC^®'")
12
Reserved Bus *34
Power Return Ground,
13
Carry No. 1
35
Reset
14
Spare
36
Gate
15
Reserved
37 Spare
*16 +12 volts
38
Coaxial
*17
—12 volts
39
Coaxial
18
Spare Bus
40 Coaxial
19
Reserved Bus
*41
115 volts ac(Neut.)
20
Spare
*42
High Quality Ground
21
Spare
G Ground Guide Pin
22
Reserved
These pins are installed and wired in parallel in the ORTEC Model 401 Modular System Bin.

The transistor types instalted in your instrument may differ from those
shown in the schematic diagram. In such cases, necessary replace
ments can be made with either the type shown in the diagram or the
type actually used in the instrument.