[sdiy] ARGHHH - PIC detunes VCOs depending on RFI *only* if USB cable plugged in

[Karl Ekdahl]

Hrrfggg... yes, so, i have a USB->CV based around a
PIC18F2455. My VCOs detune when i lift or come close
to the main powercable, but this *only* happends if
the USB cord is plugged in to the PIC board. This
happends wheter the actual v/oct from the pic board is
connected to the VCOs or not, so it seems to be going
through the powerlines... The firmware in the PIC is
allways running, usb or not, hence any possible
interference from the x-tal can be ruled out (i
guess). The PIC was first running on USB-power, but i
tried connecting it to the internal +5v rail instead
and that seemed to fix the problem - until i actually
soldered the cables in place. There might be something
wrong with the internal 5v supply (since i "designed"
it myself), it looks like this:

                43ohm 2W
+9v o---------o---xxx-----oC
        2.7K              /
+9v o---xxx---o---->|---(  ) <- NPN 2N2219A
              |           \__ 5.4v Out
 6.2v Zener-> A            E
              |
             ---
              -

My thought was that 9/2700=3mA, down to 6.2, down
about two voltage drops again through the diode and
the NPN. And then given worst case hFE i can get
75*3=225mA though the resistor only allows 9/43=209mA
which should be plenty for the pic to do its job.
Right? Did i miss anything?

I don't have a clue wheter it's the powersupply or
not, but *something* weird is going on...

thanks

Karl