FWIW.. not that it helps:

144 MHz is the American 2m ham band, for which I have a license.. I
left that out. It's not exactly in the band plan for RC aircraft but
it's not like I'd be causing real aircraft to plummet to the earth.

Thanks for the tip about capacitance. There is a trimmer cap on the
board right next to the crystal, I assumed it had something to do with
tuning the feedback but I don't even know what kind of oscillator it
was so I was hesitant to just start twisting knobs.

On Nov 2, 12:33 pm, wrote:
wrote:
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.2nd harmonic, 1st is the base frequency! IIRC 144 is ambulance service
band, here at least, so maybe not so neat. Need to show us the
oscillator circuit, otherwise can only say the osc cct needs to be
tweaked so it prefers the lower frequency. Can probably be done with a
little capacitance added to reduce closed loop gain at 144.

NT