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

[Metrophage]

Hi Paul!

Ah, happy-land-place, where after dutiful service I am enshrined in the
MOTM vault....!   >;]P 

One of the very first things I did was to test the +12/-15v supplies,
and to make certain that all of the ICs were supplied properly. It was
only after a couple of days of dumbness that I finally realized that
there should be -12v also. U12 is fine.

The 741 is more suspect, weird as I had thought the damn things were
indestructable. There is -12 volts at pin 3, but not at pin 6. Pin 6 is
+12v, as is the Q3 base. Q3 collector is indeed -28v, Q3 emitter
appears to be 0v. I suppose I can replace the 741 now, but I dread that
it might not work, and the board is just haunted! I'll go socket it
now, and see if I can dig up any 741 op amps.

I still don't understand how these parts are supposed to equal -12v and
-11v, but at least I can measure a few things. I am extremely grateful
for your suggestions.

CJ




		
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