I did a mod on my DX-390. It will disable the squelch used to
        keep the user from hearing the phase lock circuit as he/she
        changes. It also keeps a person from being able to "scan the
        band" and hear all he/she scans. Anyway, remove the cover and 
        circuit board. If the user doesn't have the external power 
        supply, they will need to remove the unit's batteries an hour
        before they do the mod. If they don't, they will believe they 
        have zapped the radio. The radio's memory needs to be fully
        discharged. After they have done this, remove C167. It's a 
        1 microfarad capacitor near the volumn control. My mod's been
        in effect for two months without any "odd" influences to the
        radio. CUL. Phil Heaton.

         
        One important thing I forgot to mention about the mod to
        the DX-390, place a jumper wire in place of C167. Sorry
        about that, rough quarter. Phil Heaton.