You said the radio was Modded..
I am guessing it had a Xtal Mod??
Make sure the X302 xtal is a 22mhz
Also Check the Microprocessor ,
If it is a UC1251, it is that original HR2600 Micro,
If it is not, it may have been replaced with a 2510/Lincoln micro,
or a chipswitch.
See if that...