Testing your laptop AC adapter

How to test a laptop AC adapter

Summary: Test a laptop AC adapter for opens and shorts with a meter.

If you need to check your laptop's AC adapter, let me show you the few simple steps to do that.

First thing to do is disconnect the plug from the wall and the computer as you will be Ohming the wires out for continuity.

Next, if your power supply disconnects from the power cord, go ahead and disconnect that as well. Now you have two separate pieces, the thick power input cord, and the power supply with the thinner cord that plugs into your laptop.

Now connect your meter while in the Ohms setting, to the two main prongs on the power cord. With the cord isolated from the power supply, you should get an open or infinity Ohms. Note: If your adapter does not disconnect in the middle, then you will be reading through the power supply, but you should still get an open here too.

Prong to Prong

Now hook the two pieces back together. Connect one meter lead to the big ground wall plug prong (that is the round one by itself), and the other meter lead to the outer shell of the laptop side plug. You should get a reading of continuity here, or zero Ohms. If you don't, then your ground is defective.

Shell to ground

STOP: Make sure the cord is not plugged into the wall, severe shock could occur or meter damage. To take the reading on the inner contacts, the easiest way is to either make a jumper wire that will fit into it, or wrap a piece of safety wire around the meter lead, and use that to stick in the contact. The last thing to check is for a direct short between the outer shell and the inner contacts of the laptop side plug. You should get a reading of infinity or very high resistance here.

Shell to inner contact

*If you are an experienced electrician (if you have not done something like this before then don't do it), then you can carefully take the jumper wire made in previous step, and insert it into the inner contact (without touching anything metal), and put the other meter lead onto the outer shell. Now connect the wall plug. In the volts DC position, you should get around 18 volts. Remember, do not touch anything metal. Note: some adapters have different voltages and polarities, check the bottom of the power adapter for your exact measurements to be sure.

If your still not sure about your adapter being defective, then try to find a friend with the same exact adapter as you. Try theirs in your laptop, not the other way around because if your adapter is defective, then you could damage their laptop, and you don't want to have to buy them a new one.

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