K40 laser wiring diagram and pinout
Most problems with the K40 laser cutter involves the power supply in one way or another.
Here is the facts about the laser power supply installed in most K40 machines with complete pinout and wiring for the different types.
The K40 is a product made with parts to make a small and cheap laser machine.
It is not developed or manufactured like this – it´s just the cheapest parts and solutions put in to a metal box.
Now when we talk about the Laser Power Supply it is actually not made to be used as it is in the K40 laser machine at all.
The power supply
There is 5-6 types of MYJG-psu´s in the K40 machines delivered, they are mostly two types with some differences on the pin layout and connector type.
In this article i will show two types who covers 95% of all types – if you have another type it is probably very close to one of the two types shown here.
Pinout / wiring
Please note – the pins are marked as they are written on the PCB. The P+ and P- are printed wrong on the Type2 PSU board – it does not matter though but they are actually the other way around.
L- Laser tube ground
FG – Case ground
AC-N – AC neutral
AC-L – AC live
GND – Ground
P+ – Together with a GND – connect flow meter, lid switch or other protection here.
IN – Signal in for power setting, 0-5 volt
5V – 5V output for use with power potentiometer or feeding the optical end stops
24V – Output for the controller board power
L – Laser fire pin.
The most common issue with the PSU´s has been the flyback transformer and/or the rectifier which has been of very low quality burning them and with arcing or no fire as a result.
You can prevent this a lot by making sure your machine is properly grounded (grounding your k40 article) – and make sure the rectifier are of a 4A model or more. Read the numbers on the rectifier to see what type you have installed. It needs soldering to be swapped.
Other problems involves no-fire issues – check out this article how to find the problem
Upgrades you should do
The priority upgrade you should do is adding more cooling to the power supply compartment. Make sure you push air in to prevent sucking smoke out of the machine. Add a 50-120mm fan and push in some air, or tilt your PSU to let it breathe air from the outside.
This prevents it from heating up the air inside the machine and trying to cool itself with the already heated air.
24V external power supply
The MYJG-40 has never been made to run the stepper motors from the internal 24V line, the internal 24V is for running your controller board and nothing else. With the K40 setup of controller you cannot have a external PSU for the motors so you need to add both the controller and motors to a new 24V PSU.
24V with 4A is enough for our machines. Read this article for installation instructions.
Replacement Flyback transformer
Before you buy a flyback – make sure yours are identical with the one you order.
Flyback transformer (external link to Aliexpress)
A PSU i personally run i every machine is the HY-T50, very stable and nice PSU without any problems. I have bought and installed at least 100 of them and what i know so far only three has been sent back for warranty claims.
HY-T50 on Aliexpress