Transmitter or crystal controlled downconverter stop operating?

Crystal oscillators can age and change tuning due to to contaminents, moisture, etc., so before you order a new crystal, try repeaking the oscillator stage trimmer cap with a DC Voltmeter at the oscillator test point. Visually check the oscillator inductor, L1, to make sure adjacent turns are not touching - you should be able to slide an Xacto knife blade inbetween each turn. If that doesn't work, unplug the crystals and check the resistance with respect to ground, at the ground or relay side of the crystal socket with an Ohm meter. If the unit is a two frequency one, it may just be that the relay contacts have some oxide build up above a few Ohms which prevents the oscillation.

If this is the case, get a 10 Ohm 10 Watt resistor from Radio Shack - 271-132. Unplug the crystals. Plug one end of the resistor into the relay side of the crystal socket you are cleaning - careful not to connect to the oscillator transistor base side. Turn on the transmitter. Clip lead the other side of the power resistor to the +13.8V and quickly flip the F1/F2 switch back and forth a few dozen times and then disconnect before your fingers get too hot to handle the resistor. Repeat with the relay side of the other crystal socket. This will put about an amp of DC current through the relay and as it makes and breaks, will burn off the oxide layer that has built up. Repeak the oscillator trimmer cap, C1. Parts aging and contamination, expecially if the user is a smoker, can cause the trimmer cap plates to be come coated with foreign matter and change capacity.