Vintage Synth Repair

Hi,

i have a Cruamr Bit-99 (black edition) i have a problem with the 6th 
voice, i hear a background note after i release the 6th, i have 
another bit99 and i exchanged the boards, seems that the problem 
comes from the P1116 Board, i heard that this is a common problem 
from this keyboards. 

anyone have an idea of the problem ? 

greetings,

oxygeno1313