Crumar Musical Instruments User Group.

> > Any idea why this component would be running so hot?
>
> Because it's died. Several of possible reasons.

My basic thinking was that if this one got damaged, perhaps there was
another component nearby that was responsible.

> 1. Check the supply. For a TL072 you should have -12v on pin 4
> and +12v on pin 8 (NOT pin 7).

Depending on the TL072, I'm getting:

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

> 2. Has it been accidentally been put in wrong way around during
> chip swapping? Easily done...

None of the TL072s are socketed, so that isn't the culprit at this
point. I was thinking of putting in sockets for all components that
are suspect so I'll be sure to be careful to that.

Backing up for a minute here, both of my Bit One keyboards had been
repaired and were functioning properly a few years ago. One of them
spontaneously developed a crackly noise problem, so it was taken out
of service. The other was stored functional for some time while I
moved, etc... Taking them out of storage, I expected to clean some
contacts and be ready to go, but instead a lot of things had
apparently failed while these instruments were in storage and unpowered.

> 3. Faulty components connected to an input or output.
>
> 4. Sometimes chips just die.
>
> First check that the power supplies are right, measured against ground
> (eg the sleeve of the output jack or a 0v test point).

I did find a 17v output on the PSU, but haven't determined if that is
incorrect and/or where that reading may be coming from. This is Pin5
of the connector going from the PSU to board P-1108.

> If the power is OK, try another TL072 and see if it's OK - they're so
> cheap it doesn't really matter if you kill another one. If the new
> TL072 doesn't get hot, measure the DC voltages on the output pins
> (1 and 7) and report back.

I need to go buy some parts, but will appreciate it if you can suggest
whether other related parts killed these TL072s.

Thanks!