[sdiy] 78xx regulator gives negative output half the time

[David G. Dixon]

> I think the problem occurs if you have assymetric loads on + and - supply,
> and if you once run into a condition with reverse
> polarity during power-up (because of charges left in some caps from
> previous powering), it latches. The diodes will bring you over
> that short moment without latching. Or some such.

I'm curious about this, because I know that some folks advocate the use of
100uF caps for power rail bypassing on every module.  I decided at the
outset of my modular activities to use 10uF caps instead, as I figured I
would get just about the same quality of bypassing, with 1/10th of the
capacitive load.  I believe that excessive parallel capacitance on the rails
is a major contributor to power-up problems, which I (knock wood) do not
seem to suffer from (yet).

So, Karl, how big are your caps?