TM 11-5840-281-35/1
Item No.
Trouble symptom
Probable trouble
Checks and corrective action
a. Observe elevation glide-path cursor
Defective CURSOR SELECT switch
25 Azimuth courseline cursor
S1104, RUNWAY switch S1109, or
abnormal or missing.
If elevation glide-path cursor is
normal, perform b and c below. If
azimuth courseline controls
(COURSELINE 1, R1126;
elevation glide-path cursor is
COURSELINE 2, R1127; OFF-SET
abnormal or missing, refer to item
1,R1121; and OFFSET 2, R1123).
no. 26.
b. Check CURSOR SELECT switch
S1104
in
applicable
Pulse
Generator O-1333/TPN-8.
c. If CURSOR SELECT switch S1104
is good, check RUNWAY switch
S1109; COURSELINE 1, R1126;
COURSELINE 2, R1127; OFFSET
1, R1121; and OFFSET 2, R1123.
Defective sawtooth generator,
26 Elevation glide-path cursor and
a.
Check for presence of cursor
sawtooth comparator, or cursor
azimuth courseline cursor
trigger at CURSOR TRIG test-point
generator circuit card in applicable
abnormal or miming.
TP2703 in sawtooth comparator
Control-Indicator C-6988/TPN-18.
circuit card. If cursor trigger is
normal, replace cursor generator
circuit card.
b. Check waveforms at REF SAW
testpoint TP2601 and CURSOR
SAW testpoint TP2602 on sawtooth
are normal, replace sawtooth
comparator circuit card.
c. If waveforms at REF SAW test-
point TP2601 or CURSOR SAW
testpoint TP2602 are abnormal,
replace sawtooth generator circuit
card.
Defective height finder fill-in circuit in
27 Excessive widening or breaks in
Replace cursor control circuit card in
cursor control circuit card.
height finder cursor.
applicable Pulse Generator O-
1333/TPN-18.
a. Defective antenna actuator ........
28 Blanked area in azimuth or
a. Refer to para 3-10.
elevation range marks miming or
b. Defective az-el blanking pulse
b. Replace az-el blanking pulse
abnormal.
generator circuit card.
generator circuit card in applicable
Pulse Generator O-1333/TPN-18.
resistance reading.
3-12. Voltage-Resistance Chart
a. Voltage and resistance measurements are an aid in
Ic. The resistance characteristics of the various silicon
determining circuit conditions and in evaluating problems
and germanium crystal diodes may be checked with a
encountered in the course of troubleshooting. Certain
multimeter or equivalent. The failure of a crystal diode in
equipment conditions must be satisfied to duplicate
a circuit is not always easily discovered during routine
conditions under which voltage and resistance
troubleshooting procedures. However, if it is suspected
measurements were made on some circuit cards and
that operational difficulties are caused by one of these
chassis. When applicable, essential instructions for
diodes after making in-circuit checks, disconnect the
duplicating these equipment conditions are given in notes
leads, being sure to dissipate excessive heat with a pair
immediately preceding the voltage-resistance data.
of pliers or other suitable tool when unsoldering diode
leads, and check the resistance characteristics. The
b. Compare the measured values of voltage and
forward resistance of all crystal diodes should not be
resistance with the typical values in the voltage-
greater than 0.5 kilohm (500 ohms). When checking-the
resistance chart (f. below). When making resistance
backward resistance of the crystal diodes, an indication
measurements at transistor pins or other points
close to maximum
connected to crystal diode circuits, the multimeter lead
connections will determine whether the forward or
backward resistance of the diode is included in the
3-15
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