The problem:
The problem is the connection between APC220 and the USB to TTL converter.
Pin number 3 (EN) on the APC220 have to be set HIGH (or floating) to power up the radio. When this pin is set LOW (<1,6V) the radio powers down. This pin is connected to the RTS-pin on the USB converter, which is causing the problem.
Arduino Serial monitor doesn’t use flow control (handshaking), so this pin is left HIGH (for several reasons I will not go into) and the radio works without problems.
Putty leaves the RTS-pin LOW when you don’t use flow control, which powers down the radio. In my experience most of the programs leaves this pin LOW.
Solution:
Some programs, like "Terminal by Bray", lets you control the pin-output manually. By changing the RTS (and/or DTR) to a LOW output, this program should work fine (Kudos Bray XD).
If you still want to use Putty or other programs which won’t work, the easy way is to just cut* pin 3 (En-pin) on the radio. A better way is to connect a cable between the radio and the converter. Only connect 5V, Gnd, Rx and TX (Except for when you need to program the radio).
- The EN-pin is used by RF-Magic. Cutting this pin makes programing trough RF-Magic impossible.