Crumar Musical Instruments User Group.

--- In crumar@yahoogroups.com, Steve Ridley <spr@...> wrote:
> 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.  

So is there supposed to be 17v coming out of the 78xx parts which are
connected to the PSU and VCF board?  I want to make sure that one of
these hasn't failed in such a way that it is sending too much voltage
and subsequently cooking parts.

In any case, I did manage to find them.  I didn't see them on the
inverted little P-1108 board (whoops) but I plan to check them out
once I hear back and get some replacements.

In the meantime, I socketed the whole VCF board and put everything
back together.  After I had it powered up for a while, one of the
original TL072's literally went up in smoke.  I am pretty sure it was
the one that was running hot before, although it ended up in a
different socket.  I had marked the IC, but put it in one of the other
TL072 sockets - so I'm hoping that means the part was bad and not the
circuit.

I do have replacements for many of the ICs on the board (not including
most of the VCFs or any VCAs) but I want to get a little more sure of
things before I smoke a bunch of new parts.

I read a data sheets on the 7805 and 7812 from my P1108 board, and
didn't see any indication that these were intended to output anything
outside of 12v or 15v.  Can you verify that 17v is okay, or could
these parts be the problem?

Thanks very much!