FP6400 schematic


Hello eveybody,

my 12 year old  FP6400 stoped working. One channel stopped working / after 5 minutes is only noise on output .

Second channel working normally.

There is +- 155V on main power supply but on power trasistors is +9V and -2 V. Second channel have +-7V.

All of the power transistor are OK

Can somebody help me ? Do anyone have the scheme then I could try to fix it myself? 
thank you