https://medium.com/@tokyohackerspace/laser-cutter-woes-15ffa6afa3a3

About 4 years ago THS raised funds to buy a cheap Chinese K40 laser cutter. These laser cutters have become very popular within the hacker/maker spaces because of their cost and hack-ability. For most of 2017 the laser cutter was inoperable. We had decided the software that came with the laser cutter had to go, and replace it with something that was open source and easier to use. We had finally achieved that goal when 3 weeks ago disaster struck. One member and a non member tried using it to cut something, and it wasn’t working. Another tried the next night with the same issue. I personally was frustrated as I had spent a lot of time working with 2 other members to get it working, and to understand the new software. I was worried that the new controller board we installed had failed. Going back to the old controller board was not an option.

Early the following Saturday one of the members who found problems with the laser cutter and I showed up at the space to debug the problem. We turned on the laser cutter loaded LaserWeb put in a piece of scrap MDF and ran the compiled g-code. The motors moved, and the power supply relay clicked. All a sign that the controller board was most likely not the problem. That left one of two things. Either the high voltage output on the power supply or the laser tube. Either one would cost us at least ¥10,000 (USD$100) to replace. Pulling the laser cutter away from the wall and removing the exhaust fan we opened up the tube housing. The question for me was how do I test a 10KV power supply without killing myself. With the laser cutter on low power I decided the first step was to just watch and see if anything could be visually seen. I honestly didn’t expect anything because lasers are invisible to the naked eye. With the laser on fairly low power I clicked the test fire button. To my surprise the laser tube glowed purple. For me this was great news. It told me the power supply was outputting voltage. Was it enough to create the laser for cutting? I didn’t know, but it was something. I then took a piece of scrap mdf and output it at the end of the laser tube and clicked the test fire again. No marks on the wood, no burn, no smoke. I had hoped that maybe the mirrors were just real dirty but having the MDF right in front of the output proved that the laser was not exiting the tube. Not wanting to accidentally injure myself I turned off the laser cutter and began to visually inspect the laser tube. I would soon discover that the output end of the tube had broken off. I hadn’t noticed it before because it is held in place by a piece of silicone tubing used for passing the cooling water from one aspect of the tube to another.