Cobra 139 LXR VERY POOR MODULATION

HI. MY COBRA 139 LXR HAS A GOOD CARRIER BUT VERY LOW OR POOR MODULATION. i AM JUST STARTING TO WORK ON CB EQUIPMENT AND DON'T A LOT OF TEST EQUIPMENT. COULD IT BE THE MODULATION POWER TRANSISTORS OR? ANY ADVICE WOULD BE HELPFUL!

THANKS IN ADVANCE, LONG NIGHT