[sdiy] MG-1 issues

[Metrophage]

Ok, I know is going on here. The MG-1 runs mostly off of a -15/+12v
supply, which is ok. But there are three places on the control PCB
where -12v is used, and this is broken. I got faked out because there
is +12v at these parts, so even though I doubted it, Grant's guess
about the filter being stuck is accurate. After a few times of checking
it, the cutoff slider is picking between +12v and +12v...

I don't understand why, but there is no -12v regulator, instead there
is a TIP30 transistor and a 741 which are supposed to yield the -12v.
Why is this? I wonder whether I should buy a TIP30 or just use a 7912,
but since I am not familiar with this sort of voltage regulation I feel
I should learn more prior to doing anything too rash.

Thanks to those who put forth some suggestions on what I should look
out for!
CJ


	
		
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