Hi bro , thank you so much for all your suggestion, that's help me a lot!!! finally I found the problem, the cause was diode D3! Replace it and I have 12vdc on both side, also the noise are gone. but still not able to get the lines in high and low to work, If I connect the guitar no sound come out! But mic1 mic2 works perfectly...I assume that the high voltage make problem to the mixer? Honestly I don't know where to start with the mixer I don't see any visible damaged..I member of the forum post the schematic of the mixer, if you could help I will appreciate. Thank you in advanceThere are two identical regulator circuits - the one with transistor Q9 produces a positive (relative to ground) voltage rail and the one with transistor Q10 produces a negative voltage rail (relative to ground). Between these two rails is a total of 24 Volts. The fuse F2 supplies -45 volts to Q10 but Q10 is not regulating the voltage and bringing it down to the required -12V as it should. Now I would compare the two circuits side by side. for example check R41 against R42, R2 against R1 and so on. I would not reconnect the faulty negative rail to the rest of the circuit until you have repaired it and it is producing -12V. -45V is much higher than the rest of the circuit is designed to receive and might cause further damage, Do you know how to test a transistor with a multimeter? It is easy and I'm sure there are videos on YouTube explaining how to do it better than I can here. Also, remember that you cannot really check components when they are wired into a circuit because you are also measuring other components. For example if you check R44 in circuit you are also measuring across C31. In other words you often need to take components out of the board at one end so you can measure it independent of other components.
Good luck!
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