Here is a general overview of my method to convert an older JR XP652 6 channel aircraft radio from 72mhz to 2.4ghz, using a combination of a DIY conversion module and some 3D printed components. Many older RC radios are still perfectly functional, and of high quality, but are becoming more difficult to continue using. This is due to reduced availability of older style receivers, and many flying clubs mandating the use of 2.4ghz systems to reduce frequency management issues.
Some radios are easy to convert if equipped with interchangeable modules on the back of the radio, but older units need a more invasive solution. Multiple companies now offer 'DIY' conversions that consist of an RF pack that can tap into existing control signals on the radio, which is what is installed in this conversion.
Step 1: Removing the Old RF Board.
On most radios, removing the RF board is actually pretty easy, in this case there were difficulties based around a factory modification on my old JR XP652. I bought this radio brand new, so I know it wasn't a later repair job. A few components were moved around on the main processor board, and a ground wire modification was done. Since the RF board had the most convenient place to solder after it was assembled, that's where it was placed. I simply moved the ground wire from the RF board to another available ground connection on another sub-board located behind the display board.
While I had the display board out, I also replaced the original lithium memory backup. If you have any models stored in memory you're going to lose them at this point. But there's no way around it. The original battery is over a decade old, and while still holding voltage, it may not have much time left. Unfortunately, sourcing a battery with the same pin dimensions proved difficult, so I got the closest I could and bent the pins to match the board layout.
Step 2: Mounting the New 2.4ghz Main Module.
Once the RF board is removed, the next step is to mount the new RF module. Since my radio doesn't have an easy to swap rear module, I had to go with a DIY style conversion. A number of them are available, this one is an Orange brand system. In addition to the module itself, there's also an indicator LED, binding button, and antenna that all needed to be mounted. I wanted something easy to reverse at a later point, so the rule was no wire cutting unless absolutely necessary.
Instead of clipping off the old connector going into the RF board, I used a .100 sized header connector as an adapter. This let me plug the new RF module directly into the original signal pins. I then 3D printed a new 'sled' to mount the conversion module in the same location as the original RF module. I made sure to give plenty of room for airflow, and a clear routing for the new antenna cable.
Step 3: Mounting the Remaining Components.
Next step was to mount the new antenna, binding button, and indicator LED. The LED was pretty simple, I just used a generic LED panel mount and 1.5mm LED available from most any large electronics supplier.
For the binding button, I again 3D printed a mount that fit it in place of the original charging jack. I opted to swap from the old NiCad battery to a more modern LiFe cell, so I wanted to remove the charging jack anyway. This left a nice and convenient location for a protected switch.
The antenna proved to be tricky, as I wanted it in the original location but the new antenna needed a shallower and smaller diameter mounting hole. Again I went with a 3-D printed sleeve mount as an adapter. The bottom half has a hex profile on the inside to hold the mounting nut, with a top cap to keep it all together. Tolerances were very tight on this, as you can see by the exposed points of the hex nut profile.
The end result, once closed up, looks like a factory original system.