I've got a JR 72 MHz transmitter module that was transmitting a very
weak signal on the correct frequency. I replaced the power transistor
and the module worked for a few minutes, but now it transmits a very
strong signal on 144 MHz. There is no signal being transmitted on 72
any more. I imagine I've got to get the crystal back into its
fundamental mode but I could use some hints. Does anyone have a service
manual or schematic for the module?

A 2m RC system would be really neat but I don't think it'll be easy to
find a receiver.