[Kenwood] TS-870S frozen frontplate commands

[Fortra]

Hi Guys,

a TS-870S from friend of mine, produced in 1998, is not allowing us to change, modes, bands, aip, actually all soft switching commands on the front plate.
Strangley enough, only MCh switch works, Lo/Hi switch and power on and off. 
It could not be reseted either partially or fully as A=B switch does not react.
Have opened the radio alnd looks for obvious, i.e. any capacitor leak, change battery of CPU, old one 3,12 V new one 3,21 Volts, check all flat ribbon cables, so with new one still does not  react, to any of front plate commands.
A friend told me, that sometimes radio retaines it's full functions but then after while it froze again!!

Any idea or clue what to check or trace for??

Thanks Nermin S58DX