[camarada78]

I have a MP573 on my bench that used to work normally.

It then got no sound at all. It was the transformer that had an open tap. I got a new one and that was fixed. 

But now i have a weird problem:

It works normally and with beautiful sound with main knob at 10 or 20 volume, after that it has no sound. From 30 and above it has no sound. if i return to 20, it works normally.

Innitially i thought it was some open resistors, but they appear to be fine. 

Does someone had this issue before?

Thanks,

Have a good day.

[JPK]

The problem is located in the first preamp stage, around Q1, Q2, Q3.
Can you report the voltages A to F shown on the image here:
https://www.soundskulptor.com/forum/index.php?topic=5.msg5#msg5

[camarada78]

Thanks for the reply.

My version of the preamp is a little different than the one of the picture.

its the rev 1.3

But, if i measured correct, the voltages are

F = 12v9
A = -9v

[camarada78]

I measured the three transistors with a component tester and they are working fine (q1, q2 and q3)

[camarada78]

I think the TL074 is weird.

Pins 3 and 12 are both with -9v and i dont think this is right.