System Board Dismantling

Let's now look at the dismantling needed before we repair the DC jack itself.

The Compaq’s motherboard must be dismantled from the chassis to access the DC jack area. Some intricate work is involved so take your time and work methodically.

Note that the magnesium alloy chassis parts are immensely strong for their low weight, but they need treating with some care to prevent damage.

motherboard to be removed from housing

The lower case moulding removed, leaving the motherboard mounted in the silver top moulding, complete with fan and (here) the memory and RTC battery still in situ.

Bluetooth cable and touchpad ribbon metal screen fixing screw

On the upperside, disconnect the Bluetooth by gently pulling its connector out with your fingernails or gently use long-nose radio pliers. (Similar audio and USB leads shown in the repair manual weren’t present on our Compaq laptop.)

The touchpad is hooked to the board via a ZIF connector. Slide the connector’s latch backwards to release it, and the ribbon will just lift out.

In order to release the system board from the silver plastic housing, remove screws  (qty. 3) – a screening screw, one located 1” left of CN4 and one through the silver plastic above CN2.

more motherboard screws more screen fixing screws

Continue removing the system board mounting screws. Two more screws (not shown in the manual) fixed the metal shield to pillars on the board the right of CN2. Remove them.

motherboard screw the system board wil llift straight out

On the laptop’s underside, remove screws (qty. 2) that fix the system board to the silver moulding. Not shown in the manual, remove one screw to the right of the fan near TC6.

Disconnect the fan/ heatsink assembly and remove mounting screws (qty. 4) from the alloy chassis. Disconnect a further flying lead (internal modem, not shown in the manual) near the power socket. (The black lead is nearest CN1).

You could use airduster aerosol to blow out the fan.

The entire motherboard with fan assembly and chassis should then lift straight out without any problem. You can grasp it by the fan.

2 screws on D conn to free alloy chassis top of motherboard
Finally, to separate the alloy chassis from the motherboard, unscrew self-tapping screws (2) each side of the external monitor D-connector. The alloy frame should now come totally away. The motherboard fully removed from the chassis and ready for inspection and repair.

The next step is to tackle the troublesome DC jack on the motherboard.

Replacing the laptop DC jack

You will need:

  • A soldering iron, say 30-40W maximum
  • desolder pump and/ or desolder  wick
  • IPA solvent cleaner
  • freezer aerosol optional
  • Dremel-type hobby drill and mini cutting disk (see text)
  • Heatsink thermal paste
  • long nose radio pliers
faulty DC jack continuity test
The first question was whether the system board had been damaged - happily it appeared to be intact. It is connected by 5 solder joints. I inserted a suitable DC plug to check for continuity between the plug & jack using a multimeter. This confirmed the DC jack was broken.
using desoldering wick stubborn DC jack!
In order to remove the jack I started with some desolder braid (solderwick/ solda-mop), trying to desolder the joints in the usual way. I also tried a desoldering pump... ... without much success! The high mass of the metalwork sinks too much heat away from the iron, so the solder doesn't melt and flow very well at all. :-(
slicing off the jack with a Dremel-type cutting disk

Not for the faint-hearted, but using e.g. a variable speed Dremel or similar hobby drill with a glassfibre metal cutting disk is the surest way of removing the jack without risking applying too much heat when desoldering.

It's no more likely to damage the board than using a small torch or similar to rework the board.

Use the jack's metal body as a 'guide plane' to keep the disk in parallel with it and gently slice through each terminal close to the metal body. Keep the disk tight up against the metal body so that you don't wander off course. Take care, keep the speed down and everything will be fine!

If you dislike the idea of cutting out the jack, then consider a small butane torch to create enough heat for desoldering with a pump.

the jack fell out desoldered PCB cleaned and ready for refitting

The jack simply fell out, leaving the five terminals readily accessible for desoldering in the usual way, using a desoldering pump. Use a freezer aerosol if necessary if you suspect overheating.

Take EXTREME CARE not to eject the desolder pump over the motherboard! I use an old aerosol cup to catch the debris. Sometimes in stubborn cases it helps to actually add fresh solder, then desolder the whole joint again in one go.

After desoldering, the corner of the board was thoroughly flushed with IPA solvent cleaner and airduster aerosol to remove every trace of metal filings.

new DC jack - note the sprung-shaped solder tags new DC jack inserted into position
The new jack being inserted into the prepared board (the right way round!) The shape of the 'sprung' terminals can be seen which hold it firmly in place during soldering.
DC jack finally soldered into place

It's a multi-layer board with lots of metal to heat, so apply as much heat with the soldering iron as you dare to help the solder flow, then the job is complete.

The solder joints were duller than I would like but there isn't much more that can be done using ordinary hand-soldering equipment. They were electrically satisfactory (and no worse than some of the manufacturer's soldering nearby!)

This completed the repair and the laptop was ready for re-assembly.

 

Re-assembly

If you followed my suggestion of sellotaping the screws onto sheets of paper in the order of removal, writing descriptions alongside, then it should be very straightforward to re-assemble the laptop in reverse order. This ensures the correct thread and length of screws are used throughout – and you’ll have no spares left over, will you? ;-)

The fan assembly was refitted and then the magnesium alloy chassis was replaced. Don't overtighten any screws, and I don't recommend using an electric screwdriver for this pupose. The modem, touchpad and the small RF connectors (Bluetooth, wifi, etc) are very fiddly so check they’re secured properly onto the system board. Cables such as Bluetooth should be re-routed into the channels designed for them in the alloy chassis.

The plastic base can then be refitted, followed by the LCD flatpanel onto its hinges.

The switch-panel and keyboard can be relocated. Take particular care with the ribbon cables which will either push into or need clamping into their ZIF connectors.

The heatsink needs refitting using a fresh uniform layer of heatsink compound to seat it fully onto the surface of the processor, and it should be tightened down in the order of diagonally-opposed screws to get the best flush fit, the same way you’d fit the wheelnuts of a car wheel.

Complete re-assembly with the processor cover, DVD drive and finally the hard drive.

Everything fitted together very precisely and all screws were refitted correctly, making re-assembly a delight and satisfyingly quick.

Final Power Up

After a thorough strip-down the laptop had been rebuilt and there were no missing or left-over screws. Having checked everything was secure, the moment of truth arrived – with the battery removed, the laptop was powered up again from the a.c. adaptor complete with new DC jack plug and socket.

The Compaq immediately sprang into life, showing the Windows XP Hibernating… screen as it woke up and rebooted without any hitch. The laptop was working perfectly again from its mains adaptor, so then the battery was inserted and charged. After a final clean-down of LCD screen and keyboard the job was done.

CONCLUSIONS

If you have some dexterity for working with fiddly things then an electronics hobbyist can tackle this sort of job - and if the laptop is going to be otherwise scrapped then you've nothing to lose by trying. A professional repairer may charge up to £150 for this job (I don't blame them!) but I rescued this valuable laptop for a few hours and less than £5 in parts. Spares are available from eBay sellers or Google for a source near you.

Having a repair manual makes a massive difference, so spend time locating one on the web. Full marks and bouquets go to HP/ Compaq for making one available on their web site.

The metal-body jack creates a few problems, and a plastic unscreened jack may be desoldered much more easily. You might not be happy about using the cutting disk but I believe it's no more aggressive than using e.g. a small butane torch. It worked perfectly for me and avoided risking more damage to the board.

The result speaks for itself: a perfect repair and re-assembly and the laptop worked first time.

Alan Winstanley.

More Resources

The Basic Soldering and Desoldering Guide - the author's #1 online guide to (de)soldering techniques

Ebay - possible source of spares and tools - search for 'laptop DC jacks' and 'opening tools'. Spare laptop screws are also often available.

Maplin Electronics - replacement DC jack plugs, service aids (IPA, airduster, heatsink grease etc).

Laptop Power Jacks - (UK) - DC jacks by mail order

Laptop Jacks - (USA) - a supplier of DC jacks

 

Photos © Alan Winstanley 2010, taken by the author with a Sony Alpha DSLR using Sony 50mm macro lens and macroflash.

High resolution versions of the photo sequence are available on CDROM for education or industry training purposes. I'm also happy to look at bespoke photography. Please contact the author for details. CDROM's shipped worldwide.

| Back to Page 1 | TOP |

EPEMag.Net is maintained independently by EPE's own Online Editor, Alan Winstanley. Since 1975 many EPE readers have 'cut their teeth' in electronics with Alan's help over the years. This independent website is designed to support EPE readers and hobby electronics enthusiasts and will provide extra background and FAQs about EPE itself.

EPEMag.Net is an ongoing project, with lots more hobby-electronics content being added over time.

Alan Winstanley.

Copyright Notice. Text and photos copyright © Alan Winstanley 2010.  Absolutely no reproduction or re-distribution in any medium without prior permission. Last updated 26th September 2010.