TM 11-6625-3053-14
6-33.
REPLACEMENT OF TRACKING POT A4R1
REMOVAL
a. Remove instrument dust cover (para 6-20).
b. Remove RF tuning head assy (para 6-23).
c.
Set frequency to 2400 MHz.
d. Remove 4 screws at top of tracing board and fold back board to expose R 1 below.
e. Loosen 2 6-32 spline screws holding mode cam to R 1 shaft. Remove mode cam.
f.
Remove mode switch by removing its 2 holding screws and hardware. Note orientation for remounting.
g. Unsolder the 4 wires going to R1 terminals 1 through 3 plus the 40% tap point. Note position of terminals for
remounting replacement.
h. Remove the 3 phillips countersink screws holding R 1 to its upper plate.
i.
Remove the R 1 pot and drive gear attached through the bottom of the A4 casting.
j.
Remove R1 pot drive gear from bottom of pot.
REPLACEMENT
a. Remount gear on bottom of replacement R1.
b. Reinstall replacement R1 through bottom of A4 casting in same orientation as noted in step g above.
c.
Attach R1 to mtg place with its 3 Phillips countersink screws.
d. Adjust backlash if any between cam drive gear and R1 gear by loosening 4 screws securing R1 mounting
plate and moving plate closer to cam drive gear if necessary. Gears should mesh smoothly with minimum
backlash.
e. Set frequency to low limit.
f.
Set multimeter to 1000 ohm range and place probes on terminals 1 and 2 of R1. Loosen R1 hub screws, and
rotate R1 shaft to obtain 400 ohm resistance measurement. Retighten gear onto R1 shaft.
g. Set frequency to extreme high. As in step f, measure resistance between terminals 2 and 3 on R 1. Reading
should be approximately 400 to 450 ohms.
h. If resistance on both ends is not equal, repeat steps f and g until resistances at ends agree within 100 ohms.
Tighten set screws on pot gear hub.
i.
Check for smooth 'reading of R1 pot by measuring resistance between wiper terminal 2 and each of the other
terminals 1 and 3 respectively.
j.
Resolder wires to pot terminals per notations of removal step g and by consulting tuning head wiring diagram
k.
Remount mode switch in original position, and place mode cam on shaft.
I.
Set frequency to 1700 MHz.
m. Using multimeter set to 100 ohm range, set probes between the common terminal and the normally closed
terminal of A4S1.
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