Crumar Musical Instruments User Group.

Is this the early or late Bit 1 we're looking at?

> I'm not detecting any continuity between ground and pins 4 or 7 on any
> of the TL072s. I am also not detecting continuity between pins 4 and
> 7 on each IC. Is that the right thing to look for?

Not really. 

> Pin 4s: -11.5v
> Pin 7s: -9.9v, 0, or +10.5 (only one 14 ICs)
> Pin 8s: 11.14v

Pins 4 and 8 look reasonably close to +12v and -12v.
Pins 1 and 7 are the two outputs (it's a dual opamp)
and -9.9v  and +10.5v are not usually god signs.

Which TL072 is it?  IC number?

>> Check for some chips called 7805/78L05 /
>> 7812/78L12/7815/78L15/7905/7912/7915 and measure their outputs. Those
>> componets have three pins and usually a heatsink installed. Left pin ist
>> the VCC input, middle is usually ground, right pin is the output. A 7805
>> should output a fixed voltage of 5 Volts, a 7905 a -negative- voltage of
>> 5 volts, a 7812=12 Volts positive etc. Same goes to the other "78" and
>> "79"-Chips. Even check their middle pin against case ground, maybe they
>> get from somewhere voltage where they shouldn´t.

Pinout of the 7912 is different from the other two.  0v is at one
end.
 
> I cannot find 780x or 781x, 

They're on the P-1108 board.  Might be near a heatsink at the 
back? (Sorry, it's 5 years since I looked inside my Bit 1).

> but there is one 7912 on the PSU board, and it measures:
> Left 0
> Middle -17v
> Right -12v

That looks good to me.

You could find and measure the 7812. Should give around +17v on 
one end, 0v in the middle and +12v at the other end.  But the
measurements on the TL072 suggest that power is getting there.
I'd remove the hot TL072, put in a socket and fit another TL072.
If it get's hot, you have a bigger problem, but they're cheap 
enough to risk it.  Buy two.  




Steve