Don Pearce wrote:
On Wed, 26 Feb 2014 18:19:58 +0000 (GMT), "Dave Plowman (News)"
wrote:

I have a bit of a block when it comes to mains transformer wirings.
;-)

Device is factory set to 120v AC 60Hz, it says on the gubbins.

It has an analogue PS with a mains transformer.

It has two primary windings wired in parallel. Red and black go to
neutral on the IEC connector, brown and orange to the on/off switch
output.

Obviously, they go to series for 240v - I assume the transformer
will be ok at 50 Hz.

What would be the best way to re-connect them for 240v?

Ie, link brown to red and 240v goes between black and orange?

Once you have the wires apart you need to identify the colours that
are opposite ends of the same winding. Use an ohm meter for that.

Assuming that the black is connected to the same winding as the brown,
connect black to neutral, then connect red to brown, leaving orange
for the live connection.


Above will give correct phasing as will following...

If black is connected to orange when tested then brown to live, black to
neutral, red to orange for series connection.