Vintage Synth Repair

Hello:
I'm having problems with the effects section on the SY99.
When the SY99 is switched on, it makes a great noise and high level distortion.
The noise is coming just from the effects section 1.
It's a sort of pops and crackles and zzzz which varies with the effect selection and don't even need to press a key to start making the noises.
Checked for bad solder joints, cleaned the plugs and sockets and replaced the internal battery on DM2 internal board.
Problem isn't solved...
If the effects bypass switch is pressed the sounds are clean.
At the moment I'm searching for a second hand DM2 board (P/N VK287500) or alternatively the DSP1 chip (P/N XF164A00, Ref.YM6007).
Any help will be appreciated!
Best regards.
José
Portugal