As mentioned, a 4-channel system may not be worth the hassle and expense to service. I recently sent in my Futaba 6XAs and was only charged $55 for inspection, repair, and retuning. If you do decide to send the radio in for service, be aware of the fact that during flying season (summer), most any service center will be pretty booked with repairs. Mine took nearly a month, but in the end I feel the expense was justified (for a 6 channel computer transmitter). What exactly is the problem you are experiencing with your radio system? I was experiencing random glitching and after testing with different receivers/crystals I concluded that the transmitter was the cause of the issue. Radio South found the issue and fixed it, and I saved myself some money by not having to send them my entire flightpack for inspection. HTH