How to determine polarity

Thread Starter


Joined Aug 29, 2008
I bought a used LCD monitor today, without a power supply.
I have some power supplies that might work.

The monitor is an HP F1703, but I cannot find the little icon that indicates positive inside - negative outside, or vise-versa, etc.

There is a small icon (a solid line underscored by a dashed line)... is that an indicator of polarity?

I've looked on HP's web site, but it's running as slow a christmas today.

In any case, how can I determine the correct polarity required of a device, when there is no apparent indicator?



Joined May 9, 2009
The solid line/dashed line indicates DC.

If you can open it up check if there is an input diode. Any good design will have a diode preventing damage from the wrong polarity. Then you can be safe in knowing you can insert the wrong tip polarity without damage. Do a continuity check using a multimeter to make sure that diode is the input diode.

On a side note, most devices are centre tip positive.