AT&T Bell System Plant Series Alignment Instructions page 2

SECTION 107-302-500
1. GENERAL
1.01
The 906A data distortion test equipment is
installed in the 20A test board ior use in
routine testing and maintenance of the narrow-
band trunks of the Bl data carrier system. This
section covers test procedures for the location of
trouble within the 906A.
1.02
Circuitry is provided within the 906A to fa-
cilitate testing of its performance. This cir-
cuitry is identified as the distortion calibrator
circuit and it provides signals of various patterns
and distortion for testing purposes.
1.03
The tests are divided into two broad catego-
ries, over-all or sectionalizing tests and
trouble location tests. The normal testing pro-
cedure is to run through the over-all tests and go
to appropriate sections in the detailed tests where-
ever part of the over-all tests fail. Detailed tests
are designed to locate the trouble to an individual
circuit package, network, or wiring.
2. PURPOSE
2.01
This section is issued to facilitate testing
of the 906A data distortion test equipment.
3. APPARATUS
3.01
The following apparatus, or its equivalent,
will be required for these tests :
• Simpson 269A VOM
• 908A Logic Circuit Test Set (J79908A)
• Hewlett-Packard type 403A AC Transistor
Voltmeter
Note: Do not ground case when making balanced
measurements.
• Extender Board of ED-73172
Page 2
4. OVER-ALL OR SECTIONALIZING TESTS
DISTORTION CALIBRATOR CIRCUIT
4.01
A distortion calibration check is included
as part of the 906A. It implements tele-
graph-type signals of various patterns and with
variable amount of distortion for checking the
performance of the distortion measuring circuit
of the 906A. The distortion calibrator consists of
CPS and the calibrator control panel.
4.02
With the switches on the control calibrator
panel in the TST, CONT (continuous hits),
and BIAS positions, a dotting signal with mark-
ing bias is generated. The amount of BIAS is con-
trolled by the DIST potentiometer.
4.03
With the switches in the TST, CONT,
and MULT (multiple hits) positions, every
start pulse is delayed, distorting all transitions
in all characters.
4.04
With the switches in the TST, INT (inter-
mittent hits), and MULT positions, a burst
of 5 distortion hits is registered intermittently.
4.05
With the switches in the TST, INT, or SGL
position, a single distortion hit is regis-
tered intermittently.
4.06
The MDM-SG switch connects the output
of the signal generator of the 906A directly
to the distortion measuring circuit, allowing for
testing those circuits without the intervening mod-
ulator and demodulator.
4.07
Table A gives switch and key settings of the
20A toll testboard and distortion calibra-
tion for the over-all tests of this part. The head-
ings at the top of the table are the same as the
designations of the appropriate keys and switches
of the 20A testboard.
4.08
The tests start with all keys normal, and,
when no setting is indicated on a subse-
quent test, the keys are to remain the same.
(---) indicates that where no designation is given
to the key position, it is returned to normal.