ab.4. Function Switch (A.C. Switch)
It is not unusual for the AC portion of the Function switch to fail with the result that the
radio cannot be turned on or off with the switch. Unfortunately, it is usually not possible
to find a replacement for the AC switch portion.
Note: it is highly recommended that power be controlled with an external power strip or
AC control panel to avoid stressing the A.C. switch.
ab.4.1. Finding a Replacement AC Switch
While the ideal solution is to locate a replacement switch (from a parts unit), this may
not always be possible. In addition, a replacement switch is subject to the same
potential failure as the original switch given the age and usage of a replacement.
ab.4.2. Replacing the AF Gain with a Control Having an AC Switch
While a non-standard fix, it is possible to replace the AF Gain control with a new
potentiometer that has an AC switch. The pot should be 500k ohms with an audio taper
and the switch should be capable of switching at least 5 amps.
ab.4.3. Modifying the Failed Switch with a Microswitch
Another option is to modify the function switch by replacing the original AC switch with a
micro-switch that is activated by the existing tab. To do this, it is necessary to
1. Disconnect the power cable from the radio.
Disconnect the two wires that go to the AC switch portion of the function switch.
Remove the existing switch from the panel by removing the knob and mounting nut and washer.
It is not necessary to disconnect the wires that go to the wafer portion of the switch.
Remove the original AC switch by removing the two nuts on the ends of the screws that hold the
switch together. Keep the switch positioned so that the screws remain in place.
Remove the switch mounting plate and then remove the switch from the mounting plate by
bending the three tabs up and removing the switch
Reinstall the mounting plate using the existing screw closest to the grounding lug.
Replace the screw opposite the grounding lug with a 4-40 x ???” . Do not install the nut yet
Bend the actuating lever on the micro switch so that it will engage the tab on the switch
mounting plate (see photo). Cut off any excess of the actuating lever to prevent binding.
Install the nut on the screw holding the micro-switch, adjust the position of the micro-switch and
actuator lever so that the micro switch switches on-off as the function switch shaft is rotated.
Servicing Procedures Page 82
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