So I found the solution. In my case the capacitor C303 by the side of IC301 on the mainboard was getting super hot and the chip didn't get the voltages it needs. After replacing it with another capacitor of the same voltage rating and capacity (100µ,10V (105°C)) but with higher temperature rating, the device works perfectly again.[br]
If anybody has the same problem, this [document|27265|Sony CFD S05 SM] document helped me to understand which chip is involved in determining the volume and where to look.