Repair Your Vehicle Battery Charger

UPDATE: Originally I published this tutorial for repairing my Bosch C3 vehicle battery charger, but 2 days after publishing this instructable, a friend of mine called me that he got the very same problem with another type of charger, and I fixed it for him the very same way. So I renamed the title to be more general, as it could solve these kind of problems possibly on several types of vehicle battery chargers.

I have a Bosch C3 intelligent charger that soon after the warranty time just stopped working.
It's a hundred-dollars intelligent charger and I really love its simplicity so I tried to search the net for a possible fix.

Unfortunately I only found dozens of complaining customers, who also bought this device and having the same problem: The device turns on, blue ring around the Mode button is illuminating, but nothing happens if you press it. (See the link about this issue at Amazon customer reviews on Bosch C3 Charger)

The illuminating blue led circle around the Mode button showed that it is powered on, so I was pretty sure that only the switch itself gone away. Being an electronic hobbyist I thought that I try disassemble and see if the switch is broken. The device is already dead, so I can't make it any worse. :) Finally I did it! The fix was successful and was relatively easy, it took 1,5 hours for me including taking the pictures. I am so happy that I could fix it, that I thought it may worth creating my 1st instructable, and help you guys out there, fixing your own Bosc C3 charger! It is a typical problem with this charger but please be advised that I cannot assure if your device has the same problem or something else!

Warning! Only try this if you are having experience in repairing electronic devices. You will need to have soldering skills to replace the switch. You will open up a circuit that can cause serious injury or even death if powered on, so as the step no. Zero, make sure you pulled out the plug from the wall outlet!!! I hope it's needless to say, detach the charging cables from the battery as well. :) Only try this instructable at your own risk! I will not take any responsibility for any possible damage you may cause!!!

Again, please double check that you have unplugged the power chord and detached the battery from the charger terminals!

First you need to open up the case by removing 6 screws that holding the case top and bottom part together.

Each of them is hidden behind a rubber plug. Just pop out those plugs with a small flat-headed screwdriver.

For disengaging the screws you will need a special tool to unscrew the 6 screws I made it from phillips head, grinding down its edges with my Dremel until I got a nice triangular shape tool that fits in the heads of those nasty special screws.

Once you have removed the 6 screws, the bottom of the box should come off with some wiggling.

Unfortunately the swith is on the very top, so you will need to lift out the boards from the case-half.

You will see 5 small bolts on the panel, but only 2 of them are holding the panels inside! Only remove these 2 philips bolts as shown in picture. The other 3 are holding the two boards together, so you don't have to remove them yet.

After removing those 2 bolts you will see that the wires are rubber-fitted through the case and their connection wires inside the box are very short.

So you won't be able to remove the panels completely but you can turn it out from its place so you will access to the other side of the board.

Once you have flipped the boards out, you will see the micro switch!

Then you will say: OMG! :) This microswitch is a very common piece, in my country (Hungary) it costs about 0.1 USD. Yes, you are reading it right, zero point 1 USD is the total cost of this repair (and a reason for a failure of a hundred-dollar device).

The switch is a 6x6mm 4-pins push-to-close type switch in SMD case, again, very common type.

It has about 3.5mm height at the top and the correct height is important, so if you are unsure, just take it out and ask for the same in your electronic store. :)

Fortunately I have couple of these switches laying around so I just take one out from my stock and replace it.

Before you go any further, you can check the switch with a multimeter to make sure it is indeed went away.

For this, just grow a 3rd hand or use something like a crocodile clip to hang your multimeter set to short-circuit-check function (when it beeps on contact) on any two pins of the switch. Two of the pins are shorted by default on both sides.

When the switch is pushed, it makes contact between the 2 pair of pins. So if you are keeping the button pushed with your 3rd hand :) the multimeter should beep between any 2 of the 4 pins. Simple as it is!

I checked mine and I was so glad that my switch was faulty!

Let's get to soldering!

As you can see, the pins of the switch is soldered onto the top of the board, so if you are in a hurry you can simply replace the switch at this point and proceed to the next step.

However I was thinking differently...

The case of the Bosch C3 is very solid and robust. Marked as IP65 at the bottom sticker, so it should be weatherproof. As you have seen the case is almost airtight, the power inlet and charging outlet wires are rubber molded, there is a rubber seal between case halves and even the screw-heads are plugged in heavily.

As you can see on picture 3, I found traces of some kind of a corrosion on several soldering points and on the board. Without knowing the reasons of these kind of corrosion exactly, I'd take a wild guess on that the reason why microswitch failure happened might also be a result of some kind of this corrosion on the metal contacts of the switch. Maybe condensational moisture, I don't know.

So to the point, I decided to separate the boards of sandwitch panel, to be able to clean it properly. Additionally, the switch can be replaced easier if you have access to the bottom too. And again, setting switch height properly is important here!

If you like me prefer to separate the panel boards, remove the 3 screw that you didn't remove previously, and set them aside in a safe place. Be careful you have not only the bolts, but also the nut, spring washer and plastic separator that keeps the distance between the two panels. One of these 3 screws can only be grab through a hole from the bottom panel side.

Once you get all the bolts out, you can de-solder the pinline that connects the 2 boards together. Be careful and patient, don't heat it very long, use your desoldering pump and heat it in shorter bursts.

Now here comes the switch change, but if you are reading this, then I'm sure I don't need to tell you how to do this.
Easiest part of the project, but if you are interested in how I did it, I will tell you in the next step. :)

After soldering, I cleaned both boards with a diluent and applied a layer of Urethan 71 coating insulator to protect the circuit from later corrosion.

When it's clean, dry and shiny, you can put the 3 bolts, plastic spacer, washer and nut back and tighten the bolts. Only when the panel is in its final place, only then solder back the pins of the pinline. I also applied the Urethan spray on the pinline after soldering.

Fortunately the factory-installed soldering points of the switch are relatively big, so you will have enough room for soldering. Apply medium temperature for according to your soldering iron, which for me was about 270 degrees Celsius space.

Heat the point in shorter bursts, do not heat one point for long! Doing so can heat up the board and components too much and may kill you C3 charger board.

Heat up the solder until it became liquid, then suck it up with your desoldering pump. Keep it going again, until you can see a the gap between soldering pins and the board. As it frees up, you will notice when you can move it straight up and away from the board.

When you removed, you can check the failure again with your multimeter, and check the replacement switch too for proper operation. Insert the switch's legs into their apropriate holes.

Don't worry about the orientation of the new switch, it is quite easy: the distance and the shape of the pins are not the same on all sides, so there are visually 2 'longer' and 2 'shorter' sides of the switch regarding the overall dimensions including the legs. You can put it in 2 equivalent ways into its place legs, but you can't really put it in a wrong direction unless you force the legs to fit in the wrong holes. :)

Put it the new switch in place and push it down fully. Bend the other ends of the legs to fit the switch tight, and solder the four pins to their posts. Solder in the new switch and clean up the area. Use a diluent to clean up everything on the board.

Now, with the new switch in place you are ready for cleaning and packaging your repaired C3! :)

Now you are ready with the tough part, just need to repeat the steps of disassembly in reverse and you are ready for a charge-up! :)

Carefully turn the panel back into its place, in the top section of the case. Be careful, and don't forget to insert that black round plastic spacer right onto the Mode button top foil before you put the board back into its place. Without that plastic spacer, you wont reach your new microswitch when pushing the Mode button, and it won't work. (Ask me how I know... :) )

You will need to play-in the board to its place. Take care about the correct alignment, the bigger board should touch the holes of the 2 screws, and the high voltage cable (right side of the case) should be aligned correctly in their guides just as it was before.

If succeeded, you can tighten back the 2 screws, put on the back cover, and fasten the 6 case-screws with your triangle-shaped special tool. Don't forget to insert the 6 small rupper plug above the case screws!

Congratulations, you made it, and let's hope that you made it well! Try to charge a battery!

No suprise, it is live again, and charges just fine! :D

I hope you enjoyed my first instructable, please feel free to ask any questions!