I just hacked into the JR MAX-44 four channel transmitter and added the fifth channel by connecting a switch as shown in first two pictures attached.

I knew it transmits six PPM pulses as the fifth and sixth channel servo holds the position to one extreme. I looked for some pictures of MAX-66 PCB connections on the web and by short circuiting the T15 and T13 terminals on the PCB found the fifth channel.

I was expecting the same for sixth channel on the other end of PCB for terminal T15D and T14 as shown in third picture but it did not work. I do not have oscilloscope to observe the correct signals, so if someone out there has experience or equipment to dig into this I am pretty sure to convert this to six channel radio.

Note: The same post exist in Aircraft-General > Radios > Add Channel switch, but since the thread is too old that’s why this has been reposted here!