There are many tutorials on removing the door cart and the panel to reach the door lock. So I will skip those steps.
The Switch And The Problem
Switch is near the bottom of the unit and can easily be traced as blue/red wires go to it.There are several ways the switch is broken. Sometimes the plunger goes off or the rubber seal breaks down and corrodes inside the switch.
In my case it looked like switch was somehow swollen a little bit and maybe the metal pieces of the lock was slightly deformed. As such, the plunger was not under the lock piece which should press it down. When the switch is half way out, the lock piece is not able to push it down. As can be seen below.
The white part is the seal and black round piece on top is the plunger. It is suppose to be pressed down by the black lock piece but switch is half way out of position.
Whatever the reason, the best solution is to change the switch. There are few types of the switch and few different ways it is installed. Older locks have melted tabs which keep the switch in position where newer locks have latches which allow switch to be removed.
Also there are repair kits. For me the right door switch kit code was 3BD 998 786. I obtained a replacement switch from AliExpress. This switch was the latest model which has a metal piece to support the plunger and increase contact area!
3BD 998 786 comes with crimp butt connectors which allow you to cut the wires and reconnect. However I did not use them.
Seperating Electrical And Mechanical Parts
Lock unit has 2 parts. One part houses all the mechanical parts and other part has microswitches, motor etc. First we must separate these to be able to access the solder points of the red/blue microswitch wires.First remove the microswitch from the mechanical part. It could be in place by plastic tabs, metal retainer or plastic latches.
Then, you need to remove 2 screws and pull the outside door handle latch completely open. Below are these marked with red arrows.
After removing the screws, you need to pull the door handle latch completely and keep it open.
Now you can wiggle the pieces and separate them.
Removing Circuit Board
The circuit board is inside the plastic box. You need to remove the torx screws around it. There are 9 screws to remove. After this, you can pry open the box. It may feel like it is glued due to the seal inside. However, you can slowly open it.Make sure to separate the pieces slowly so parts will not fall out.
Desoldering And Resoldering Wires
The circuit board is covered with some sort of resin for moisture protection. That is why the board and solder joints looks dark/red in the photos.First settle the board carefully using helping hands.
Now you can melt the solder and pull the wires out.
Once the wires are removed, clean the surrounding area first. Then, you can put the replacement part's wires in place and also use flux for a good connection.
Once the connection is made, you should re-coat the circuit. You can use any kind of non-conductive lacquer for water proofing. But best is to use some sort of conformal coating. I used plastic spray for electronics boards.
Simply, I first masked the area and then sprayed over it. It should be good enough for a while.
Reassembling The Lock
Reassembling the lock is simply reverse of the disassembly. You need to re-attach the microswitch to mechanical piece using the same method as original switch was assembled. Mine used melted tabs, so I had to use plastic weld glue to create tab pieces on top.Final Result
The switch with the metal helper sits so much better in place and I expect it to work for many years to come. You can see the difference below at door locked and opened positions.Door locked:
Door opened:
Clearly the new type switch works so much better compared to the older type.
