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APPENDIX C Modifications to the Digital Interface Box
C.1 Modifying the Polarity of the Interrogation Pulse
Consult drawings 650110 and 250068 before performing the following procedure.
C.2 Changing Recirculations
1. Remove the 4 cover screws on the DIB.
2. Locate the jumper wire in the center of the PCB attached to “0” and some other number ranging from
1 to 8. There are 8 possible points.
3. Use the chart below to change from 0 to X to get N (number of desired (re)circulations).
4. Install U3 (74161) for recirculations above 8.
Jumper N
(From 0 to X) (No. of circulations)
0 to 1 1
0 to 2 2
0 to 3 4
0 to 4 8
0 to 5 16
0 to 6 32
0 to 7 64
0 to 8 128
NOTE:
Any DIB having a high number of circu-
lations can be changed to a lower num-
ber without having an effect on the inter-
rogation pulse timing.
From INTERNAL to EXTERNAL interrogation
1. Remove the 4 cover screws from the DIB.
2. Remove cover with PCB connected. Turn component side
up with J1 to the left and J2 to the right as you face the
board.
3. Remove the 555 timer from the bottom of the 16-pin DIP
socket (position U1B— Pins 1-4 and 13-16).
4. Install a 9637 IC* on the top side of the same 16-pin DIP
socket (position U1 Pins 5-8 and 9-12).
5. Install a 100Ω resistor between Pins D and E of J1 10-pin
connector (or E1 and E2).
From EXTERNAL to INTERNAL Interrogation
1. Remove the 4 cover screws from the DIB.
2. Remove cover with PCB connected. Turn component side
up with J1 to the left and J2 to the right as you face the
board.
3. Remove the 9637 IC from the top side of the 16-pin DIP
socket (position U1B Pins 5-8 and 9-12).
4. Install a 555 timer** on the bottom side of the same 16-
pin DIP socket (position U1 Pins 1-4 and 13-16).
5. Install the proper value resistor (or next highest available
value) in R1 location. Use the following formula to deter-
mine the resistor value:
R1 (KΩ) - [T(msec) x 14.43] - 1
6. Install R2 (499Ω), C1 (0.1µF) and C13 (0.01µF) if R1 is not
present.
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