FP6400 schematic

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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