Malcolm,
You could try with a voltmeter.
Check for continuity between the pins and some metal part of the chassis.

The pin that has continuity will be the negative one.

Another way that could work is to test the pins with the voltmeter set to
diode test.
Put one lead on each pin, then reverse them.
If you get about 0.600 one way, and open reading the other way, then your
positive pin is going to be the one with the red voltmeter lead when the
voltmeter reads open.
If you get values that do not match the above, then I would post them here
before trying to plug it in.

Got2Go

"ML" wrote in message
...
Does anyone know the connector polarity for a Sharp A250 notebook please?
I
have been given one without the external power unit and I want to test it
before buying a new PS. The notebook label specifies an EA-J02V 22v
1.8Amp
ac adaptor, that connects with a 3.5/1.35mm connector.

I need to know is the center pin positive or negative to chassis?

TIA
Malcolm L
Somerset UK