If the regulators are more than a couple of inches from the power supply
capacitors, there is a recommendation that you place a 1uF Tant. capacitor
on the input and output of the regulator.  These regulators will
occasionally break into a high frequency oscillation that can give some
rather screwy voltages.  This may not be your problem - but it will not hurt
to try.

David V. Fansler
Network Administrator
AutoCyte, Inc.
336-222-9707 Ext. 261
dfansler@autocyte.com
Now Showing! www.mindspring.com\~dfansler\


                -----Original Message-----
                From:   Dave Johnson [mailto:djohnson@SIRIUS.COM]
                Sent:   Saturday, February 27, 1999 3:32 PM
                To:     PICLIST@MITVMA.MIT.EDU
                Subject:        [OT]Linear V-Reg Weirdness

                I just built a power supply that provides +6V, +5V, +3V, and
-6V, using
                several linear regulators, 2 of which are 7806 and 7906 (for
the +6 and
                -6). Sometimes it's fine, but sometimes when I turn it on
the +6 supply
                doesn't appear, and hovers around -0.8V instead.

                I vaguely remember reading about this problem somewhere in
the dim and
                distant past, but I can't for the life of me remember the
trick to fix
                it. I tried putting asymmetric loads on the outputs, but
that doesn't
                seem to do it. Can anyone shed some light on this for me?

                Dave Johnson