TM 11-5805-424-15/NAVSHIPS 0967-220-9010/TO 31W2-2G-41
(3) Remove the jumper to the -15-volt source and
c. Cut off transistor Qa by momentarily shorting its
jumper the input side of each input element to
base to emitter, and check the voltage at the collector of
ground. The voltage at the collector of the
transistor Qb.
The voltage indication should be
transistor should indicate approximately -15
approximately 0 volt. If not, check for open resistor Rc
volts de for the AND gate shown in C and 0 volt
or Re or defective transistor Qb.
for the AND gate shown in D. If not, check for
f. Cut off transistor Qb by momentarily shorting its
shorted collector load resistor, shorted base
base to emitter, and check the voltage at the collector of
return resistor or diode, or shorted transistor.
transistor Qa.
The voltage indication should be
(4) Remove the jumper from each input resistor in
approximately 0 volt. If not, check for open resistor Rd
turn, returning the input resistor to the -15-volt
or Rf or defective transistor Qa.
source. With any input element of the AND
g. If proper results are obtained in b through f
gate shown in C returned to - 15 volts de, the
above, check the steering circuit by removing power
collector voltage of the transistor should indicate
from the unit and checking the forward resistalnce of
approximately 0 volt; with any input element of
diodes CRc and CRd (the resistance measured should
the AND gate shown in D returned to ground,
be in the order from 1 to 10 ohms). Check for defective
the collector voltage of the transistor should
input capacitor Ca or C11, or defective steering resistor
indicate approximately 0 volt. If not, check for
Rg or Rh.
an open input element.
6-6. Isolating Troubles in Logic Gates
b. AND Gate, GAS-( ) Type (B, fig. 5-5).
(1) Connect the ME-26A/U between the output of
the gate and ground.
Troubleshooting procedures for each type of logic gate
(2) Jumper the input side of resistor Ra to a -15-volt
are given below. Refer to the appropriate schematic
source. (Refer to the applicable schematic
diagrams for specific reference designations and
diagram and PC card layout for this voltage
component values. All procedures are performed with
point.)
the applicable PC card extended and with power
applied.
(3) Alternately jumper the input side of capacitor Ca
a. Inverting AND Gate (GAI-( ) Type).
to -15-volt source and then to ground. The ME-
26A/U should indicate 0 volt at all times. If not,
The AND gates shown in C and D, figure 5-5, operate
check for open resistor Ra or shorted diode
essentially the same. The main difference is that the
CRa.
AND gate shown in C requires two positive inputs to be
enabled, and the AND gate shown in D requires two
(4) Jumper the input side of resistor Ra to ground,
negative inputs to be enabled.
and alternately jumper the input side of
Check the gates as follows:
capacitor Ca to -15-volt source. The ME-26A/UI
(1) Jumper the input side of each input element to a
should indicate some negative value when the
source of - 15 volts de. (Refer to the applicable
input is negative, and 0 volt when the input is
schematic diagram and PC card layout for this
ground. If not, check for open capacitor Ca or
voltage point.)
open diode CRa.
c. AND Gate, GAD-( ) Type (A, fig. 5-5).
(2) Check the voltage at the collector of the
transistor. The voltage indication should be
(1) Jumper the input side of each diode to a - 15-
approximately zero for the AND gate shown in
volt source (refer to the applicable schematic
C, and approximately -15 for the AND gate
diagram and PC card layout), and check the
shown in D. If not, check for open collector load
voltage between the output of the gate and
resistor, defective base return resistor or diode,
ground. The voltage indication should be a
or open transistor. (For the type shown in C,
negative potential of less than - 15 volts. If not,
check for open resistor Ra, open resistor Rb, or
resistor Ra.)
shorted diode CRa or CRb.
6-54
