The replacement motor vendor sells a cache of old stock at an ever higher price, as of 2019 $500. You probably already noticed that Velux’s new operators don’t work on old windows, and new windows and operators will be more than $500. Repair may be a good choice, especially if you need more than one.
The KEM140 breaks for 3 reasons.
1 There is a 1n4001 diode that fails short circuit and it moves an inch at a time. Its only pennies you just need an electronics hobbyist to solder a new one.
2 There is a micro-switch to detect if the cover is off and if the screen is not in place. The switch contacts can fail and the lever can bend so that it’s always disabling the motor. The micro-switch arm can be re-shaped or the switch itself can be replaced. There are part numbers on the side of the switch and manufacturer’s marking, but there are so many nearly identical switches it may be easier to pick one from a catalog by the mounting hole locations and actuator. You want one that has normally open contacts that close when the mechanism is pressed.
3 The plastic gear that engages the skylight scissor mechanism can break resulting in a running motor that makes clump-clump sounds but nothing moves. If you take the whole assembly to a local machine shop (or two) you’ll find someone who can mend or replace the broken gear. It’s not that there aren’t catalogs of full of available gears, a catalog gear needs to be modified to drive the skylight scissor.
4 Don’t overlook a non-functioning controller. A motor not fed power doesn’t do anything. The switch pad lights should blink. There should be voltage on the wires that head to the motor when it should be moving (at least briefly)
5 Finally, the scissor mechanism may have failed. The vendor that sells the KEM140 also has scissor mechanisms. If not broken it very likely needs lubrication to avoid overstressing the motor unit, a stearate thickened waterproof white lithium grease at the pivots and slides, e.g. Aqualube or Jack’s something or other. A waterproof boat trailer wheel bearing grease is a good 2nd choice. Silicone grease of any type is never a good choice for a mechanical lubricant, it is always a silicone oil plus finely ground silica which is unhelpful under any pressure. It has fantastic electrical insulating properties and amazing resistance to water absorption and wash-out, but it’s not a lubricant for metal pivots and slides under pressure.
Oliver Street, September 2019
