Sometimes, after 70-plus years of use, you find you need to rebuild or repair Marx switches. Although Marx didn’t design them with repairs in mind, you can fix them. It’s not hard.
First things first: The control panel is at least as prone to fail as the switches. Test your switch by connecting one wire from a transformer to the center post, then touching the other wire to each of the outer posts, one at a time. If the switch works that way, it should work on your layout too. If it doesn’t work after you connect it to the control panel, it’s the control panel that’s broken, not the switch or switches. A modern Atlas controller works perfectly with Marx switches.
If I’d known this in 1986, I would have had a lot more fun with Dad’s trains. His switches worked but his controller didn’t. They’re on my layout now though.
The other problems that can happen with Marx switches are a dead spot on the pivoting rails, burned out solenoids, short circuits, or physical damage.
All but physical damage are easy to fix and often require very little in the way of parts. Marx made these about as simply as they possibly could in order to keep costs down, and that makes them easy to work on today and cheap to repair, usually.
Opening the switch
Flip the switch over and you’ll see there are two brass eyelets that hold it together. Drill out the two eyelets and pop the bottom off.
A series of tabs hold the cover over the solenoids. I circled them in red and yellow in the picture to the right. Straighten the tabs and lift it off to gain access to the solenoids if you need to. But if you don’t need to access the solenoids, there’s no reason to remove that top cover.
Fixing dead rails
Check the piece of copper foil that’s under the pivoting rails. In the picture to the right, it’s the big green circle. If that piece is crinkled or bent, the rails can lose power, causing the train to reverse or go into neutral. Straighten the piece and clean it with some metal polish. Clean the underside of the rails that contact that piece as well. Putting a drop of Rail-Zip on it will make it work longer in between cleanings by increasing conductivity and protecting against oxidation. One drop is all it takes.
Also double-check all of the solder connections. If any of the wires are lose, re-solder them to match how they look in the picture.
If the solenoids don’t work anymore, you can replace them. But first, make sure the problem isn’t the terminals. Check the terminals for corrosion. I always just replace them, no matter what. The terminals are the three 8-32 slotted screws in the photo above. You can replace them with half-inch 8-32 machine screws. I always replace the nuts and the washers too. Old, dull, dirty, rusty screws conduct electricity poorly. Replacing them reduces voltage drop and makes the switch snap much better.
If the solenoids still don’t snap responsively after you replace the terminals, you can lubricate the sliding plate, which you can see to the left. It’s the piece with the slot that the solenoid slides into. Spray a bit of Teflon spray lubricant on it to free it up. Teflon lubricant won’t gum up or gather dust or dirt over time. The treatment will make the switch pivot a bit more freely so the solenoid doesn’t have to exert quite as much force in order to lock. When the solenoid fires, the pivot rails should lock into place and not turn by hand.
If lubrication isn’t enough or the solenoid is completely dead, you’ll need to replace the solenoid assembly. The cheapest way to do that is to find a switch that’s in poor mechanical condition but still has good solenoids. Marx switches are plentiful on Ebay.
Bend out the tabs circled in green in the photo above, note where the wires go, and carefully swap the donor solenoids in. Wire the replacement up the same way the old one was.
If you prefer, it is possible to rewind solenoids with new magnet wire, but I haven’t done that myself yet. The last time I priced magnet wire, it wasn’t that much cheaper than just buying a donor switch.
On rare occasions, a switch can develop a short circuit. If that happens, examine the wires on the underside for damaged insulation. You can repair damaged insulation or just remove the damaged wire and replace it with new wire, whichever you’re more comfortable doing.
The other thing that can cause a short circuit is damaged tape on the lower plate. If the tape is missing, you can usually tell where it goes from the tape residue. Cover it with a new piece of tape. Or if you want to really go the extra mile, cut a piece of kraft paper from a brown grocery bag to cover the entire lower portion of the switch. Brown kraft paper is an excellent insulator, after all.
At some point, one of Dad’s switches got stepped on and the rails that pivot don’t line up correctly anymore. Once that happens, there’s no good way to fix it. The solenoids still worked, so I put its solenoids in a dead switch. The metal Marx switches aren’t expensive so there’s no shame in buying another one and using a damaged one for parts.
While working on the switch, you might as well make it look nice. Clean the painted surfaces with a damp cloth and a mild detergent. If the paint is dull or chipped, consider freshening it with a new coat. I don’t bother stripping the old paint. I just carefully brush a thin coat of satin black or red paint, as appropriate, over the old surfaces. It doesn’t make them look brand new, but it makes them look nicer on the layout.
Repainting your switches theoretically makes them less collectible, but if they aren’t pristine, they have no collector value anyway. Their value is in their function, so I repaint my switches before putting them on the layout. The layout looks nicer that way.
Closing the switch back up
The solenoid cover snaps back into place rather easily. I twist the tabs just enough to hold the cover, rather than bending the tabs completely. That lessens the chances of them snapping off.
The bottom plate fits into place rather snugly, but I still secure it. If you’re careful, a short 6-32 screw will fit in the holes in the switch where the eyelets originally were, and they’ll thread in and hold the switch together. I prefer to use 3/8-inch 4-40 machine screws with nuts. This way, if I ever have to work on the switch again, I can use a screwdriver next time instead of a drill.