Laptop Power Adapter and Supply – Illustrated how to repair laptop power cords
Friday, February 3rd, 2012 |
One day your laptop may refuse to power on even though the AC adapter is plugged in. You’ve probably noticed that your laptop features an LED that lights up when live power is attached and the battery is charging, usually on the front of the laptop body. Older power adapters may also have a status LED to show they are functioning. The AC adapter may have failed if it’s plugged into a good power outlet and the cable ends are securely seated in both the adapter and the laptop but power LED doesn’t come on. Yet it’s more likely the failure is the power lead from the adapter to the laptop. Your laptop may use a straight plug, like Toshiba and Lenovo, or an “L” connector like some Compaq and HP models, or a special proprietary design like some Dell and Sony adapter. The straight in power connectors probably have the highest failure rate because the cord often droops at a sharp angle. |
| Try wiggling the cord a few inches back from the laptop jack and and see if the power LED on the laptop blinks. If the LED is unsteady or if it only lights if you position the cord a certain way, either the receptacle in the laptop or the wiring to the connector has failed. If you could choose, a bad cord is a much easier problem to repair, and that’s what the illustrations on this page describe. Sometimes you won’t see any sign of damage on a bad power cord no matter how closely you look because the insulation is unbroken. But the stranded wire inside the insulation could have frayed to the point that it only makes intermittent contact and melts open from current. The cable is normally shielded coax, with the inside conductor soldered to the inside of a barrel connector, and the coax shield soldered to the outside of the barrel connector. The solder joints are inside the molded plastic connector. |  |
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The AC power cord that attaches the adapter to a wall outlet almost never fails as long as it’s plugged in solidly. Laptop power cords usually include a ferrite choke to help prevent RF generated in the laptop from flowing back up the ground shield and turning it into a broadcast antenna. If it’s too close to the molded connector to allow for replacement, I cut it off and hope nobody complains about interference. While you can always strip coaxial cable with a knife, it pays to own a decent wire stripper so you can make a clean job of it. I remove around 1″ of the insulator from the braided shield and then twist the wires together off to one side. Classy technicians may tin the braid with a little solder before proceeding, but it’s not really necessary if the connector has a tab with a hole. |
| There’s no point trying to reuse the original molded connector unless you are absolutely desperate, in which case you’ll be stuck shaving away the plastic with a box cutter. I’ve had to do this while overseas when I couldn’t find a replacement, but it was a bit of a mess since the ground braid was soldered directly to the outside barrel of the connector on the Toshiba I owned. And it can be tough to resolder manufactured connectors without melting everything because they aren’t intended for multiple use. In the U.S. you can still find barrel connectors at Radio Shack, but bring along the original connector and the laptop to make sure you get the size right. You can often find the exact inner and outer diameter in millimeters (they’re all metric) by searching on the Internet for AC adapter product descriptions for your laptop. |  |
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Before you solder on the new connector, make sure you slide the plastic shell onto the cord in the proper orientation. It won’t fit over the connector after the fact and you’ll have to unsolder it all if you forget. If the shell doesn’t fit onto the cord or your new connector doesn’t include a shell, you can fake one up with many turns of electric tape. I generally leave enough room so the connector can fit into the laptop power jack as far as it will go, but good electrical contact is made before it’s completely seated. In the picture I show the yellow inner conductor of the coax soldered to the tab that corresponds the center conductor of the barrel connector. The silver braid is soldered to the tab which corresponds to the outside of the barrel connector. You can use heat shrink tube over the tabs, if you have it, or even use a couple heat shrink layers in place of a shell. |
| I tend not to trust the connector shell so I work a little electrical tape in between the two tabs to make sure they can’t get crushed together and short. The trick is leaving enough room to get the shell over it all. The shell can be screwed onto connector since both pieces are threaded. After my first experience when I was forced to carve up a molded connector with a razor blade while travelling, I starting keeping a spare ready made in my laptop case. If the AC adapter cord I’m using fails, I can just cut off the end and splice on the replacement by twisting the wires together. The main failure mechanism for these cords is from the cord drooping down and flexing around when you work on your lap or run the laptop at the edge of a table. |  |
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The problem shown on this page, a frayed or broken power adapter, is easy to diagnose. But most laptop issues benefit from careful troubleshooting before you rush to spend money on parts. The Laptop Repair Workbook is focused on troubleshooting laptop hardware. It includes an introductory section on all power and charging related problems, followed by an advanced flowchart for troubleshooting battery charging and AC power operation. The 191 page printable eBook version can be purchased for instant download anywhere in the world at about half the cost of buying the paperback and paying for shipping. |
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