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Laptop power problems are not uncommon, but it may not be obvious whether it's the battery or the mains adapter or the laptop itself to blame. Here's the help you need.

Summary

If your laptop won't power-on, won't charge, or immediately or randomly powers-off again, it may not be obvious whether the fault is with the laptop, the battery or the power adapter. Simple tests described here should tell you which needs repair or replacement.

Safety

Before proceeding, please note:

• Unsuitable replacement batteries can be dangerous
• Poor quality replacement mains adapters can be dangerous
• Attempting to open and repair a mains adapter can be dangerous.

(These points are further elaborated in the text below.)

Diagnosis

A faulty power supply or battery is a relatively common problem with laptops. Your first aim should be to try and determine which, if either, is at fault.

Most if not all laptops will run happily with no battery, so long as they are plugged into the mains. Take out the battery and see if the laptop will run just on the mains adapter. If so, the battery is almost certainly dead or dying.

Conversely, see whether the laptop will run on the battery alone. If so, the problem is with the mains adapter or its lead, or the power socket on the laptop. (If your battery is already fully discharged you might have to ask around to see if you can find someone with a laptop using the same or a similar adapter that you could try.)

Some laptop power adapters have a power light. If this remains extinguished, the adapter is almost certainly dead. But before discarding it, check the fuse in the mains lead, and check that the mains lead itself is serviceable.

There are many different types of laptop mains adapter, but manufacturers tend to use one type for a range of similar models. If you need to try one which isn't identical to the original, firstly, make sure the plug is the same size. (A slightly oversized plug might damage the socket on the laptop.) Next, examine the label on the adapter and make sure its output voltage is the same, or at least within 1V. Lastly, make sure it's output current (in Amps) or power (in Watts) is the same as yours or greater.

Problems can be caused by a fault in the low voltage output lead from the power adapter to the laptop plug, especially if this lead has been habitually twisted or wound around the adapter body. With the adapter plugged into the laptop (or connected to a multimeter), try bending the lead at various points while watching to see whether the power or charging light on the laptop flickers or comes on. Pay particular attention to vulnerable points in the lead such as close to any kinks, close the the adapter itself and close to the plug at the laptop end of the lead. Check for visible damage to the plug itself.

The power socket in the laptop can also get damaged. Try wiggling the plug in the socket to see whether that has any effect.

If you are unsure of the state of the battery, a small utility BatteryInfoView will display the status information held in the chip included in all laptop batteries.

If you still haven't located the problem, then it may be a fault on the motherboard. By all means disassemble the laptop to see whether there is anything obvious, such as failing electrolytic capacitors (see the capacitors page for details), or any components which have clearly overheated, or physical damage. If the laptop powers on but powers off again within a few seconds, it could be that the heatsink is no longer making efficient thermal contact with the processor, allowing it to overheat and automatically shutdown.

Repair

Replacement laptop batteries are available from a variety of sources, but the quality may be variable. In the worst case, a knock-off battery from an unscrupulous dealer and using a slightly different chemistry to the branded one could be a highly dangerous fire risk. Lithium batteries have a limited shelf life, so even a genuine branded battery might give poor performance if it's been in storage for a number of years. Wherever possible, always buy from a reputable seller, and make sure you can return at the vendor's expense it if it turns out to be faulty.

Replacement mains adapters, too, are readily available, but the same warnings about quality and safety apply. The best option might be to try and obtain an original adapter from another laptop of the same model that has died.

Laptop mains adapters are not designed to be repairable. Their cases are generally glued together very firmly as they would be highly dangerous if they came apart through an accident or incompetent tampering. For the same reason, whilst repair may not be totally out of the question, it must not be attempted unless you are completely competent in the repair and in securing the case again afterwards.

If the cable on the laptop side of the adapter is damaged it may be possible to cut out the damaged section, but you will need to take care to ensure that a replacement plug has the same internal and external dimensions.

If the power socket on the laptop is damaged, it may be possible to bend the springy metal leaves inside the connector in order to make better contact using a pin or similar tool.

In some laptops the power socket is connected to the motherboard via a flying lead, and the socket and flying lead may be available as a spare part. In others, it's soldered directly to the motherboard, in which case obtaining and fitting a replacement may be harder.

If you think the heatsink bonding to the processor may have failed, there are YouTube videos and other online resources showing how to clean off the old heatsink compound and how to apply the new. If you don't do it properly you could easily make matters worse.

Spare Parts

An eBay search will will throw up various sources of laptop batteries and mains adapters, but pay careful attention to the seller's reputation. If you purchase a replacement battery, make sure the vendor will accept returns in the case of poor quality parts.

If you search for a common replacement part such as a screen or keyboard, you will generally find several vendors who refurbish cast-off company laptops, and who may well be able to help with other parts such as a power socket.