So , I will answer myself as it can be usefull for anyone having the same issue.
I found that the 8vREF signal was around 17mV and not 8V. This 8VREF is used on 2 opamp, on the lm3915 of the vu meter and …as a voltage reference on the LM1131 dolby chip. From the schematic, i suspected a faulty capacitor (C417 on dolby PCB) and… I was right. It was short cut so i swapped it with a brand new one and everything works fine now!