So Your Laser Won't Fire?
The laser power and control system in a K40 is a relatively complex and its the most unreliable subsystem of the overall K40. Therefore a lot of time is spent diagnosing and subsequently replacing and repairing parts of this subsystem.
It seems important that we capture what we have learned about troubleshooting and fixing K40's.
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Is it your laser power or the laser tube that is bad?
Good question! We don't have a definitive way of pointing to a bad tube but we can insure that the control system that drives it is working properly. Well almost. We can verify operation all the way to the input of the LPS but beyond that the HV characteristics of the laser tubes drive makes clear component identification dangerous, uncertain and expensive.
This guide helps eliminate everything up to and including the input of the LPS as the culprit. If everything is good to the LPS then I would:
- Replace the LPS
- If you have certain symptoms you can try replacing the LPS's HVT. This is the most common type of LPS failure
- Replace the laser tube
The K40 Laser Power System Troubleshooting Guide
This guide provides K40 owners a flow chart for troubleshooting the Laser Power Control and Supply subsystem.
The Guide To Troubleshooting
The Elements of a K40 Laser Power Control Subsystem
- Input power
- AC plug and fuse
- Control panel
- Current control pot or digital controls
- Laser enable sw
- Laser fire Test button
- AC power button
- The high voltage supply
- The laser enable loop
- The local test PB
- PWM input (L)
- Local power control (IN)
- PWM generator
- The controller that converts gcode S commands to a PWM signal.
- The laser tube that generates the optical power
Hints of Tube & LPS Failures
If after you check your laser power system with the troubleshooting guide and all is OK here are some additional hints:
Your tube might be bad if:
- It does not light up at all
- There is an arc from the anode to the frame. When the tube is bad it provides no load to the LPS. An unloaded (bad tube) LPS will often arch violently to the surrounding case
- It has cracks
- There is no current on the meter when the test switch is activated.
Your LPS might be bad if:
- There is arching inside the supply
- The mili-ammeter reads erratically at currents above 4ma
- The current is lower at higher power settings than at lower power settings
If you find any kind of error or lack of clarity please make a suggested change in the comments.
Enjoy and comment,