PMu getting too hot same as OSD

[paktazh]

I just finished with my WKM V1 with RCtimer ESC and Motor and 6s lipo and DJI OSD so i did a couple of successful flight with 6s then I tried to change 6s to 4s I connected the battery and then connected to PC changed it to 4s so it was ok no problem but once i went outside and reconnected the 4s i notice that smoke is coming out of OSD i disconnected the battery immediately and got home back and opened the hexa to find out why i disconnected the osd completely and i noticed that the PMU get to hot and the and the RX does not turn on and when i connected to the pc some of the motor start which should not the main controller light comes on get red so it should be ok I change the RX but still no green light in RX and the software shows RX error too any help will be appreciated by the way the red light is not flashing either by the way I build a WKM before with no problem but this time I add a OSD even though i did everything according to DJI diagram but i think that was the cause but still not sure

 

[paktazh]

Updated
Today i checked my FPV camera that was connected to the OSD with my multimeter since it was connected to different battery and only the negative wire and the signal wire was going to OSD and one line from the camera negative black wire and positive was going to a 12 v lipo so i connected the camera again the same way to find out if the camera was short or something and that may caused that i found out that the negative and signal wire of the camera was giving one volt power in the wire that was connected to dji osd i checked that with my multimeter so what do you think is that normal or that can cause short circuit please help need your help to find out thanks