The K40 machines, or sometimes named 3020 stamp engraver comes from a country where most of the assemblers don´t have the skill and knowledge about electrics as they should.

The CE and FDA markings on the machine are fake.

Before you do anything at all, do not plug in your laser into the wall socket.
Go through this checklist!
This is no joke, the power in this machine can and will kill you if there is slightly wrong with it, and there is numerous reports of bad connections and cables in the wrong spots.

Tools needed

– Flashlight
– Multimeter
– Small scewdriver flathead/philips head

Checklist

1: Check the wall socket cable
If you have 3 prong connector, measure all three on both sides on the cable.
Put one of the leads from the multimeter on one side of the cable, and the other lead on the other side. Set the multimeter to resistance (ohm). You should see 0.0 or a beep that it´s closed. Do this on all three prongs in the cable.

2: Loose cables
Check inside the machine for any visible loose cables. If you cannot find them, check out Troubleshooting to see where it should be fitted.

3: The supplied fan
Do NOT connect this to mains outlet without opening the small hatch on the fan, check all connections. Put on heatshrink tube if needed.
More about this in the Exhaust articles

4: Grounding the laser.
If you have 3-prong cable, and your outlet has 3 connectors you do not need a separate ground wire. Check all grounds inside the machine. Remove the ground bolt in the back, clean away the paint so it has proper metal connection and put it back. Remove all kind of plastic or nylon washers, make sure you have good metal contact.
If you only use 2 prongs, you need to ground your laser properly. Depending on your house electricity system, consult a electrician or ask in the Facebook group.
Do not ground the machine on the ground bolt on the back if you have ground in your house system. Different ground potentials may damage the electronics.
If you are unsure about the grounding in your house – consult a electrician.
Never trust me, or anyone else in regards of live mains power status of your house if you are unsure, always, always consult a certified electrician who can look at your setup.

5: Water pump
This is just a suggestion with a warning, but when your laser is on, do not put any body part into the cooling water.
If the pump isolation breaks, the water will have live mains power in it.
The laser tube also creates some static electricity and it hurts badly if unlucky.
More about this in the Watercooling articles

Final suggestions

If you are going to add more functions to this machine, lights, red dot pointers, displays and other electrical products. Do not wire it into the PSU of the machine.
It sure have power to handle a small LED, but if something happen with the machine you have no clue if the added periphals was to blame or not.
Buy a extra small wall wart, they are cheap and you can assure yourself that if something happens, it isn´t because of the additions you made.