Vintage Synth Repair

hello

happy to get my roland jx10p

but this one has a default

when i power up i have the message on the screen roland jx10/SE but stay on this message

i have checked the battery, it is ok , i have measured 3.3 v on

then i check the power supply all are ok +15,-15, +5, -5, and +7 unreg

do you have any idea where i can start my investigation cpu board ? rom ? contact ?

i see on the cpu board stranges solder on the transistor Q4

i notice also two wire on the screen board but i suppose is to pick up the gnd signal

any idea

thanks