The origional UV-K5 ( now referred to a Version 1 [v1] ) utilised a DP32G030 MCU. Supply of the DP32G030 became difficult so a replacement processor: the PY32F030 was utilised, resulting in v2 of the UV-K5. A limited number of the v2 were produced before the processor was upgraded to the PY32F071, resulting in v3 of the UV-K5. The PY32F071 has double the flash and ram memories of the origional MCU.
The implications of the MCU replacement are that the v2 and v3 radios are not compatible with various community developed firmwares that have been developed for the origional (v1) UV-K5.
The v2 and v3 radios are identified with the applicable V2 or V3 marking either on the radio serial number label or on the radio frame in the area of the serial number label.
If a v2 or v3 radio is flashed with a community firmware developed for the v1 radio, the radio will become unresponsive. The bootloader, however, should still be operational and the origional factory firmware can be reloaded to return the radio to functional.
As of this time, forks of F4HWN firmware has been modified to work with the v2. The conversion has been produced by Vincent and is available at https://github.com/muzkr/uv-k5-firmware-custom
Developemnt of firmware for the v3 is progressing and should be available soon. The mcu used in the v3 is also used in the new UV-K1, so it is reasonable to assume more effort will be put into firmwares for this processor compare to the PY32F030 used in the v2 UV-K5 radio.
Armel, F4HWN has indicated the increased memory of the PY32F071 MCU will allow him to include all his developments in one firmware. Currently owing to code space limitations, Armel has built serveral firmware versions with different features.