I can't think of any reason why they can't add a 1n4007 diode. It's way
overratted for the needs of the scope and will stop any polarity
problems
dead.

No, it's UNDER-rated! It is a 1 Amp diode and your earlier figures
indicate over 2 Amps when 2 axis slewing.

Oh yeah, no problem. I've seen diodes that can take huge amount of power.

The only reason why they didn't (that I can think of) is that there
is a 0.2 (I think it's 0.2 anyway) voltage drop over the diode which
might
affect the performance of the scope.

The forward voltage drop will be more like 0.8volts at rated current.

That's worse that I thought, suppose I should have checked the figures.
That'll go some way to explaining why they didn't bother - loosing .8 of a
volt when running on 'C' Cells will make the batteries appear drained really
quickly (like it's not a problem anyway) the scope needs every bit of the
12V.


Basically No reason at all.

Other than those, no. 8¬)

A better solution is to wire a 12VDC relay in series with a small diode
(the 1n4007 above would do) and place that arrangement across the
supplies' input wires, checking that the relay actuates when the red
wire is attached to the +ve pole of the battery.

Wire up the relay contacts to connect the supply to the load through the
contacts which close when the relay is energised - these are the n.o
(normally open) contacts.


Yep. That'll do it.

Regards

Colin Dawson
www.cjdawson.com