[sdiy] MG-1 How to get -12v from TIP30 and 741?

[Metrophage]

The MG-1 is still limping along. As I had mentioned last week, the
filter is not working because there is no -12v supply from the keyboard
PCB.

This is getting stupid now, as I have no idea what is supposed to be
going on here! For +12v and -15v there are just 78M12 and 79M15 after
the rectifier and filter caps. For -12v though the raw negative voltage
is supposed to be converted by going through a TIP30 transistor and a
741 op amp. No go, as I am getting +12v instead. Replacing the TIP30
and 741 makes no difference, though the new filter caps might make it
happy.

Is there any good reason for providing -12v this way, instead of a 7912
voltage regulator? There are only three places in the control PCB where
-12 is needed: the sharp/flat pot, the VCO2 detune slider, and the
filter slider. I don't know how much current is required for these
things. If somebody would explain how the
-12v is supposed to work I would be very grateful!

CJ


		
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