Märklin Switch Mechanisms (Motors) and the Digital World: A Fix

A well known Märklin train issue is with their switch motors. The turnouts on their HO system can be motorized and even digitalized with accessories that they have made available. The switch motors can be used in both the analog world or in the digital world. In the analog layout, the switch mechanism must have a protection against overheating should the switch solenoid stay in the ON position too long. It will overheat and could cause a fire. Not good! To remedy this, Märklin has installed two miniature delimiter switches inside the switch motor mechanism.  The trouble with these micro switches is that they use silver contacts. Silver will corrode with time and the oxidized silver will make a film that prevents the switch from working. One can only imagine that this process would be accelerated in a higher humidity environment (like a basement!).  Well, my switches, some 23 of them, have started to fail due to this issue.  

Now, we all love the internet. One can find nearly anything out there…. including fixes to this very problem. My solution is NOT new. I didn’t invent it, but I found references to it, and even a video or two. Hopefully this post will spread the word.  In a digital environment, which most Märklin users are living in today, the switches cannot get into a state of endless current application.  The digital command is only 250ms long by design.  Once can therefore safely short out the mini switches inside the motor and have a working mechanism again!  

The process is simple enough. Remove the switch motor from the turnout. Remove the metal protective cover and remove the motor and place on your work area. Solder across the two (sometimes three) terminals of the mini switches: there are two in each mechanism. TEST the assembly and then return to the case and attach to your turnout again.  In the image above you will see the work space all ready to go. The mechanism is outside of the black metal case and is ready to be fixed. 

Here is a closeup of the mechanism. It is basically a solenoid device which actuates when the digital decoder gets a signal from the system to turn the voltage on to this coil set. The coil then drives the bar one way or the other to switch the turnout. As this bar slides, it hits the two micro switches on either side to delimit current flow to prevent overload. We do not worry about this with a digital system, so we can short out the contact circled above in red. I used a small piece of braided wire that had been tinned with solder prior to application.  It is ok to short out the center contact as well. No worries there. 

Above is the shorted mini switch contact. All that has to be done here is to snip off the extra red wire from the short and then repeat for the other mini switch. 

The completed short is shown above. Care should be taken to avoid any inadvertent solder bridges that could short to the other circuitry in the mechanism, or to the metal case in which the mechanism is enclosed. 

The last step – and one for safety! – mark the outside of the case clearly so that anyone else tempted to use this switch mechanism knows that it is for digital layouts only and no longer safely useable on analog layouts. Burning solenoids smell very bad, and a layout could potentially catch fire.