Fusible Link Repair

18v LXT Battery Repair – Chip Reset

By Ryan Flint – April 2013

Introduction

The Makita range of battery power tools are undoubtedly the best tools on the market, with the range and availability unparalleled by any other brand.  Unfortunately in the 18v LXT range for the general user the batteries have a tendency to fail and become useless.  As an Electrician/Engineer I thought there would be plenty of solutions to this problem….. 

I have searched the internet in hope that I could find a solution to my faulty batteries, I have contacted Makita agents and supposed repair centres all giving me the same advice.  Throwing them away and buy new ones...

I decided to ignore their advice and to have a play around with them and think I have a solution to some of the problems.  Please note that this solution is not for all problems and that this will void all warranty.  If your battery is less than 12 months old and you have a proof of purchase I advise you to go through the proper channels and have your battery replaced by Makita.

The common red/green flashing fault on the 18v Makita Charger

Some basic electronic skills and tools such as a soldering iron, multi-meter and basic hand tools are required for this procedure.   

Opening the battery

To open the battery you will require a small flat head screw driver and a T10 long torx bit.  Firstly you will notice a white tamper proof bung in one of the screw holes.  Flick this out with a screw driver and toss it, this will no longer be required.  The 4 screws are all that hold the top of the battery in place.  Remove the top and the white clip (Be careful of the spring under the clip, it could cause a possible short).  You now should see a similar view to Figure 1.

Figure 1

Testing the Cells

To test the voltage of each cell use a multi meter and test the voltage between the 6 points shown in Figure 2.  Each cell when fully charged should have close to 4 volts in it (point 1 to 2) but in most cases we will see much less.  Check between points to make sure none of the cells have gone to zero.  If one of the cells has gone to zero, the cell will need to be replaced before any further repair can be done.  You may have several batteries with a faulty cell and my advice is to create a battery from the spares. (Example: make 3 from 4)

Figure 2

Removing the Circuit Board

To remove the board several joints need to be un-soldered and parts removed.  Listed below are the items that need attention.

                                  1.       Positive Terminal - unsolder from the board 

                                       2.       Negative Terminal – unsolder from the board

                                       3.       Temp Sensor – glued in (need to lever out, be careful not to damage)

                                       4.       Ribbon Cable – remove

                                 5.       Screw – removed

Once these parts have been attended to the board should be able to be removed from the battery pack.  The temperature sensor (point 3 in Figure 3) is glued into place and becomes the hardest part to remove, be careful not to snap the probe from the board.  The ribbon cable (point 4) is very delicate and also needs careful attention.  At all times be careful not to short any parts of the board or cell pack while removing the board.

Figure 3

Repairing the Fusible Link

The fusible link being blown has been the cause of the problem on three of my batteries to date.  I have not been able to find any circuit diagrams online to actually understand what the fuse supplies but I assume it is the supply to the chip itself. 

The fusible link has a black cap (noted F03 on my board) that can be flicked off with a screwdriver showing the metal parts.  A solder blob was the applied to the top of the chip to bridge out the blown section.  This should have hopefully of fixed the problem.   

By bypassing the fuse (shown in Figure 6) we have supplied the chip with power again and in my case it solved the problem.  However as you are bypassing a fuse the next time such fault occurs there will probably be irreversible damage to the electronics, so far all is running well in the repaired battery!

Figure 4 - Underneath the board

Figure 5 - Cap flicked off

Figure 6 - Soldered repair of the fuse

Re-Installing the board

The board can now be reinstalled into the cell pack and the pack put back together and placed into a charger.  A handy hint on reinstalling the circuit board is installing the ribbon cable first as it is quite difficult once soldered and screwed back in.  Hopefully your battery pack comes back up to full voltage and runs for many more cycles giving the Makita tools the customer satisfaction they deserve!

Ryan Flint 31/03/2013