How to repair a laptop DC jack - a step by step takedown!
One of the commonest causes of damage to laptops arises when its DC power lead is wrenched out at an angle to the motherboard– maybe someone trips over it or it’s pulled out carelessly. They can also wear out over time.
This special EPEMag.Net web article shows you how to repair the DC jack of a typical laptop. I'll start with initial basic tests, then show how to stripdown and solder in a new jack, with photos (easier to take in at your own pace than any video!) showing everything step by step.
Repairing a DC Jack on a Compaq laptop
In extreme cases, the laptop’s motherboard can be wrecked due to a DC jack being ripped out carelessly. A repair is often non-viable due to the high price of a new board, assuming spares are obtainable anyway. A DC jack might cost £150 ($225) fitted by a shop.
However, if the motherboard and laptop itself is still intact, then an electronics hobbyist can often repair the DC jack if you have the necessary skills and tools. A damaged laptop can be salvaged for just a pound or dollar or two and a few hours of your time.
In the real-life strip-down example shown here, a Compaq Presario v4000 series laptop had suffered damage to its DC jack after taking a nasty knock. Some simple tests confirmed the likely damage: I found that the laptop worked from its battery for a time, which proved that the laptop motherboard was intact, but the DC plug on the a.c. adaptor was bent if not broken.
Basic Requirements and Initial Tests
Apart from needing some dexterity, a clear and well-lit workspace is desirable and it helps to work very methodically, so try to set aside a few clear hours if you can.
You’ll only need a few hand tools and service aids together with a soldering iron or station, desoldering materials and maybe – for reasons you’ll see later – a mini hobbyist rotary tool such as a Dremel might be handy. Maybe you can borrow them if you don’t already own them.
When trying to fault-find, I tested the simple and obvious things first.
- Why was the battery not recharging? Was the a.c. adaptor broken? Testing the adaptor’s DC plug with a voltmeter showed zero volts output, so I checked the mains plug fuse first (it was OK).
- Then I checked for a DC voltage again by stripping back insulation near the damaged DC plug and I obtained a correct voltage reading: so the a.c. adaptor was OK but the DC plug obviously needed replacing. If the a.c. adaptor was still faulty, I would have swapped it for another rather than bother trying to fix it. They're often sealed units not worth messing with.
- Importantly, I also tried the laptop with a spare a.c. adaptor, but that did not power up the laptop either (remove the battery and see if the laptop runs from the mains).
So apart from a broken DC plug to fix, there were two more potential problems, either (i) the DC jack socket on the laptop needed attention and/ or (ii) the motherboard was damaged as power wasn't getting through. Consequently the laptop would have to be stripped down to find the power fault.
I tackled the a.c. adaptor first. I admit that I hate replacing DC power plugs on a.c. adaptors, partly because there are so many variants (style, internal & external diameters, and length/ reach), which makes getting spare parts difficult. Worse, the internals are never very good to solder (try soldering thick cables onto those flimsy little solder terminals!), and the cable entry & retention can be very poor, meaning that a replacement plug is never as substantial or reliable as the original moulded-on plug was.
The Compaq laptop’s a.c. adaptor plug was repaired using a DC plug from Maplin Electronics. I’d googled for "Compaq v4000" and found the jackplug dimensions 1.65mm x 5mm dia., so I found a 1.7mm x 4.75mm, near enough. The repair sequence is shown below.
|The a.c. adaptor label shows the polarity markings of the DC plug - usually the centre is positive, as depicted here. It's the inner centre pin and so the plug's outer metal 'sleeve' is negative.||(Top) body of new plug slid over the stripped DC cable prior to being soldered. Do it straight away while you remember! (Underneath) the old bent DC plug chopped off. Test the cable polarity with a DC voltmeter if you need to.|
|Firstly the centre (positive) wire was soldered to the centre pin of the replacement plug. The braid (negative lead) is cut to length so its end aligns with the plug's other solder terminal (i.e. the big metal sleeve)...||The braided wire soldered to the main 'sleeve' terminal. Don't overheat it or you'll melt the plug's plastic mouldings and wreck it - they're not very robust.|
|Close-up photo of the repair. I tinned the end of the braid and the plug terminal separately, then used a reflow solder technique to melt them both together while holding them together with long-nose pliers. A little insulating tape (not shown) around the centre conductor is a good idea.||The sleeve is threaded back again and the plug is ready for use. The cable retention crimp wasn't much use with this thick cable. The repair can't match the original moulded-on plug but will be adequate if it's not abused.|
How to repair a laptop's DC jack
Recall that with the battery removed, the laptop didn’t run from any a.c. adaptor, so the question was whether the laptop’s DC jack socket was faulty or whether the motherboard was damaged (or both).
The first stage was to obtain a repair manual for the Compaq v4000, which would simplify the job enormously, so my advice is to spend time googling to locate a manual (either for this laptop or a very similar model). Happily, I found it online at HP's web site (it’s the HP Pavilion dv4000 manual, also suitable for our Compaq Presario V4000 notebook), and I printed off the PDF. This would make a massive difference to the job.
I also sourced a spare new DC jack for the motherboard. There are scores of variants but by searching the laptop model number I found an eBay seller listed spare DC connectors (great!) so for just a few pounds I got my hands on the correct part. You could google for laptop parts sellers too.
In order to replace the DC jack it’s necessary to totally disassemble the laptop and see what we’d find inside. The next series of notes and photos show step by step what was involved.
I prefer to use a large anti-static bench mat grounded to earth, wearing an anti-static wristband for maximum ESD protection. A clear work area and good lighting are valuable.
Note re: laptop screws: usually a small precision Philips screwdriver is ideal for most of the disassembly. Laptop screws usually have blue threadlock adhesive to prevent them loosening due to vibration or flexing. It’s not necessary to apply new threadlock.
Metric screws are measured by their diameter and length, such as M2 x 7.0mm – a 2mm diameter shank screw that’s 7mm long, excluding the head. Several sizes are used on a typical laptop. Rarely the pitch is also stated (the distance between the ‘peaks’ of the thread) but standardised pitches are generally used.
DAMAGE CAN BE CAUSED BY RE-FITTING SCREWS OF INCORRECT LENGTH. THEY MAY LOOK VERY SIMILAR BUT WILL HAVE DIFFERENT HEADS OR LENGTHS.
TIP: to make sure screws didn’t get lost or mixed up, I sellotaped them to a sheet of paper in the order that I removed them, with a quick description written alongside them. I soon had three pages of notes with the screws carefully taped alongside. I also jotted down the page numbers of the repair manual, so I could pinpoint what goes where. It worked for me!
- Small Phillips precision screwdriver
- Maybe, special driver such as TORX No. 6
- Air duster aerosol
- IPA (Isopropyl Alcohol or similar solvent cleaner)
- Ideally, a plastic prying-apart tool (eBay)
- A notebook and some sellotape!
A laptop is a very precisely engineered unit and everything usually fits together very closely. Start by removing every peripheral you can from the laptop, starting with the battery. Then I removed screws in the following order, helped by the excellent manual, sellotaping them onto a notebook and scribbling a note.
|Remove hard drive cover (2 screws), then pull out the hard drive in its cradle and store safely.||Optical drive retention screw (qty. 1) was then revealed so remove it.|
|Use a straightened paper clip (I used a jeweller's screwdriver) to eject the DVD tray through its tiny Eject hole, and then the DVD drive will slide out fully.||Processor’s heatsink cover (not Phillips but a T6 screw instead. Luckily I had a TORX driver). Prise off the heatsink cover with a prying tool or flat screwdriver and remove to reveal the CPU heatsink.|
|Heatsink retainer screws (qty. 4). Wobble the heatsink to break the grease seal and it will come away. Clean it with an airduster and remove all traces of thermal grease with e.g. IPA solvent. Avoid eye contact!|
|The CPU heatsink removed to reveal the processor underneath. A small area of heatsink compound ensures a close fit onto the CPU for maximum heat transfer. I left the CPU in place. Note the fan grille nearby.|
Next, locate the laptop switch-panel on top, remove its retention screws (qty. 3) on the back edge of the laptop’s underside. Open and fold out the LCD display as flat as possible.
To remove the switch-panel, hold down the keyboard’s Insert key and gently ping off the switch-panel at the right end using a plastic tool or blade, gently tilting it forward towards the LCD. Do NOT force down the keyboard key but use your fingertip to cushion it and lever off with a screwdriver.. Then unhook the switch-panel near the F1 key and F6/ F7 keys. Do NOT pull it off! Loosen and let it rest as it’s still connected by a delicate ribbon cable near the F6/ F7 keys.
|The laptop’s keyboard retention screws (qty. 4) are revealed and removed next (located by the F1, F5, F11 and Insert keys). TAKE CARE not to damage the fragile ribbon cable. The switch-panel pulls out 7-8mm. Very gently lever or ‘spring’ it out at the left and right edges and hinge out the keyboard towards the front. Bring the loose switch panel with it, though it disconnects separately.|
|Release the zero-insertion force (ZIF) connector on the motherboard that retains the keyboard ribbon cable, and gently slide out the flexible ribbon. The keyboard can now be removed completely.|
|Likewise disconnect the switch-panel ribbon cable, and it can now be safely removed and put aside.|
|Remove the access panel for the memory and wireless board. The memory board can be unclipped and slid out at an angle. It only fits one way.|
Two tiny screened cables connect to the wireless board, so gently unclip them from the two gold-plated coaxial connectors. Note which one is which. The white wire was the ‘aux’ J2 and the black wire the ‘main’ J1. They are routed through the chassis along various channels and cable clips etc. and need to be teased out completely before the LCD can be removed, because the RF antenna is in the LCD panel.
|The wireless board can be released and swivelled out at an angle. It only fits one way. The same is true of the memory module. The RTC clock battery (blue) is underneath and I left it in place for now.|
The stereo loudspeaker connections are disconnected next. Pull them gently from the header.
The LCD panel ribbon cable can be disconnected by pulling from the main board.
If it adheres anywhere, gently unpeel it from the chassis moulding, so the cable hangs free.
A CRITICAL stage: remove screws (qty. 2) on the underside that fix the locating pillars of the LCD's hinges to the base. SUPPORT THE LCD AT THIS TIME TO PREVENT IT COMING AWAY.
A total of four screws (two per hinge) secure the hinges onto the base unit. I propped it up on a block of foam rubber, until the display was free and could be lifted away. Store it safely away to avoid damage or scratches.
On the laptop’s top side, three screws are removed, on the alloy bracket near the display connector (qty.1) and longer screws (qty. 2) on the metal screening.
Underneath the laptop, a total of 15 screws of various diameters and lengths are removed next, including two that were not shown in the manual.
Again, it’s best to note down what goes where to ensure easy re-assembly, and sellotape them onto your notepad. The repair manual is invaluable.
If you are sure all fixing screws have been removed from the plastic base, gently prise apart the black base from the silver body, starting at the battery area. I strongly recommend a plastic disassembly tool, e.g. a nylon spatula, or a special plectrum-style plastic tool, NOT a metal blade or you’ll damage the plastic housing. When prying apart the two case halves, do not pry off accidentally and damage the slots that the battery engage into.
After prising apart the bottom, it should just lift straight off. If it doesn’t then you haven’t removed all the necessary screws.
The lower case moulding removed, revealing the motherboard, complete with fan and (in my case) the memory and RTC battery to be removed from the silver upper housing next.
Continue on to Page 2 - Stripdown of the motherboard, then desoldering the faulty DC jack and inserting the new part.
Copyright Notice. Text and photos copyright © Alan Winstanley 2010. Absolutely no reproduction or re-distribution in any medium without prior permission. Last updated 24th September 2010.