the as-15 does not protect the camera from high trigger voltages.  it
just converts the hotshoe to a pc cord.

according to:
<http://www.botzilla.com/photo/strobeVolts.html>
the trigger voltage of a vivitar 285 can be as high as 350v.  that
would fry the nikon.  if your camera still works, then yours probably
isn't that high.  best to test it to be sure.

if you want high trigger voltage protection, you need a wein safe sync:
<http://www.weinproducts.com/safesyncs.htm>

nikon, of course, will only recommend nikon flashes.  other flashes
work fine, but they won't do ttl with the camera (unless they
specifically support i-ttl, which a scant few do).

The Nikon AS-15 DOES NOT provide high sync voltage protection.  It simply
gives you a PC terminal connection to use with recommended flash units so a
sync cord can be used for triggering those flashes with cameras that only
have a hot shoe and no PC connection.
That is why only Nikon flashes are recommended.  That way you will not
exceed the recommended flash sync voltage and damage your camera.
Bob

According to Don JM  <minnie4@primus.ca>:

    The AS-15 offers *no* protection.  It is just a simple adaptor.
It connects the center contact in the shoe to the center contact of the
PC connector, and the side rails of the shoe to the outer contact of the
PC connector. (From back in the days when "PC" meant "Prontor-Compur"
instead of later "Printed Circuit", and later "Personal Computer", and
currently short for "PCMCIA Card". :-)

    If you want to verify this, and have a small (jeweler's size)
Phillips screwdriver, remove the two black-headed screws in the corners
beside the "foot", and examine what is in there -- just the connectors
and wire -- nothing protective at all.

    Now -- if you have electronic test equipment (in particular, a
voltmeter or a multimeter), fire up your flash and measure the voltage
between the shell and the center pin of the PC connector from the flash.
The negative probe should go to the shell, and the positive probe to the
center pin.  If the meter needle tries to go downscale (below zero) than
the polarity of the connector is wrong for the D70.  If it goes up,
check the voltage, and compare it to the listed maximum voltage in the
camera's manual.  I forget whether it is 100 V or 150 V.

    Of course, you know that the iTTL metering of the camera won't
work with this flash, so you'll have to use auto mode, or purely manual.
(And in either case, be sure to turn off AUTO-ISO (if you have it
enabled) because the flash's auto mode, or your calculations, will
expect a constant ISO.

    Sorry for the bad news,
        DoN.

The instructions that came with your camera say to use only Nikon accessories.