On Sun, 4 Mar 2007 09:16:54 -0500, "Dimitrios Paskoudniakis"
wrote:

I have a Black&Decker electric hedge trimmer - you know the kind, with the
thumb safety, the index finger trigger, and the 2-3 ft long shears, which
operates on electrical power from a cord plugged into an outlet.

All of a sudden the unit keeps cutting off even with the trigger held. The
cord is firmly seated for electrical continuity. At one point I had severed
the power cord, repaired it, so was thinking it was the cord, but even with
a new replacement cord the symptom persists, and I do get the intermittent
brief "on" with the original cord. The original cord does provide power for
other things, so it is not the cord, but perhaps the severing shorted
something in the trimmer?

No, the way it works when you put a piece of metal through the
electric cord is that either it touches both wires at the same time or
it doesn't.

If it doesn't it still might cut one of the wires, so the cord doesn't
work again, and that wire has to be repaired.

If it does touch both wires at the same time, you are likely to blow a
fuse in your basement, and you may also cause a pop or a burn where
the blade cuts the wires, and you may even find copper balls at the
end of the wires where the copper melted and then hardened again. But
all the current that is going through this "short circuit" is power
that is NOT going through the trimmer itself. So the trimmer is
getting less current through it at that time, none or almost none at
all, because the current takes the shorter, easier, path.

It's also possible if the blade touches both wires at the same time
that it won't make good contact with one or both, and only some
current will flow through. It may not melt either of the wires in
two, and it may not even trip the circuit breaker or blow the fuse.
But again, this won't cause more current to flow through the trimmer.
The electrical resistance of the trimmer determines the maximum amount
of current that flows through it. Even a bad-contact short circuit
might lower the amount available from the wall to the trimmer, but it
won't increase it.

So all this had no effect on the trimmer.

Here's the peculiarity: If I rotate the unit so that it is upside down, it
runs. As soon as I rotate it rightside up, it conks out again.

Both of the other answers seem to figure it's not the switch. They
probably have more experience on this problem than I and might well be
right. But I'm thinking maybe your hand on the switch changes in some
way when you twist your arm, and then the swtich works. So I would
try, with the trimmer unplugged, tying the swtich down with a string
or a wire or plastic tie, plugging it in and seeing it not run, then
turning it over without touching the switch.

I have about 4 B&D trimmers in the basement that I got at yard sales
or out of the trash, and I haven't had trouble with either the switch
or the brushes. I think the case has to be opened to replace either,
so just be careful to note, or to make a sketch, which holes have the
short screws and which have the long ones, and just after the case is
opened gently, how the wire is routed through the handle, where it
bends around the plastic ribs, where/how the switch is held in place.

The case determines all this, but it can be hard to tell after the
wire is out of place.

Any ideas as to what this is, and if it is easily repairable, or do I just
need to buy a new one?