Boss Laser Not Firing? Here's the Exact 6-Step Checklist I Use After Wasting $890 on Misdiagnoses

Who This Checklist Is For (And Who It's Not)

If your Boss Laser suddenly stopped firing mid-job—or you're staring at a new-to-you used machine that won't even produce a test dot—this checklist is for you. I'm a production manager who's been handling custom engraving orders since 2018, and I've personally documented 12 distinct "not firing" scenarios. The worst one cost me $890 in replacement parts I didn't need (note to self: always test the power supply before swapping tubes).

But if your laser is still under warranty and you haven't run a basic multimeter test yet, skip this and call Boss Laser support first. This list is for people who've already ruled out the obvious or who are dealing with a machine that's out of warranty (like mine, a 2019 LS-1420).

The 6-Step Checklist (Follow in Order)

Step 1: Power Supply Voltage — The 80% Culprit

Start with the easiest thing: measure the DC voltage coming out of your power supply to the laser tube (CO2) or to the driver (fiber). I use a Fluke 87V, but any decent multimeter works.

• CO2 machines: Expect around 24V at the control board input, and for the laser power supply (the big one) you should see 300-400V DC on the output when firing is commanded. If you see zero, the PSU is likely dead or the interlock circuit is open.
• Fiber machines: The driver input voltage is typically 24V or 48V. If it's missing, check the main power relay and emergency stop switch.

What most people don't realize is that a failing power supply can still show nominal voltage at idle but drop under load. I've tested three "dead" PSUs that read fine with no load but collapsed to 50V when the tube tried to fire. (This happened in September 2022 on a $3,200 order — every single piece had to be redone.)

Quick check: If your laser fires a weak pulse sometimes but not always, suspect the PSU before the tube.

Step 2: Laser Tube Condition — The Expensive Assumption

It's tempting to think "not firing = dead tube." But here's the complexity: CO2 tubes degrade, they don't usually die instantly. A tube that's lost 70% of its power might still fire but be too weak to cut or mark. A truly dead tube typically shows external signs: cracked glass, melted solder at the electrodes, or discolored coolant.

To test: run a manual test fire at low power (10-15%) and listen for a high-frequency hiss. No sound? The tube is likely open-circuit. Use a high-voltage probe (not your regular multimeter — the 15kV+ will destroy it) to check for voltage across the tube terminals when you fire. If voltage is present but no beam, the tube is dead. If voltage is absent, the PSU isn't sending power (see Step 1).

I once ordered a replacement tube for $650, installed it, still nothing. The real issue? A tiny crack in the interlock wire connector that only showed up under vibration. （Not that I'm proud of that — $650 and three days of downtime.)

Step 3: Coolant Flow & Temperature Switches

Here's something vendors won't tell you: many Boss Laser machines use a simple flow switch that can get stuck by mineral deposits or air bubbles. If the flow switch doesn't detect water movement, the machine won't fire — even if the pump is running. This is especially common in areas with hard water.

Check for:

• Air in the coolant lines (bleed the system)
• A stuck float in the flow switch (tap it gently)
• Chiller temperature — if the coolant is above 35°C, some controllers auto-disable firing. This happened to me during a summer batch of acrylic cutting (circa July 2023).

The most frustrating part of this: you'll hear the pump running, see water in the reservoir, and assume everything's fine. But the sensor may not agree. Always verify the flow indicator on the return line or use a separate temp gauge.

Step 4: Controller & Software Communication

If hardware passes, the issue might be digital. For Boss Laser machines using Ruida controllers (most common), check:

• USB cable: swapped for a shielded one? Long runs over 2m can cause dropouts. (I switched to a 1.5m cable with ferrite cores — $12 fix that saved me two weeks of intermittent failures.)
• LightBurn output settings: wrong laser type selected, or the PWM frequency is set to something the PSU can't handle. For CO2, 20kHz is standard; for fiber, 40-100kHz depending on material.
• Test fire button: in LightBurn, the "Test" button bypasses the file buffer. If it fires in Test but not in a job, the issue is in your layer settings (power too low, or the layer is set to "air assist only").

I've personally caught 47 potential errors in the past 18 months using a pre-flight checklist I printed and laminated next to the computer. The most common? Forgetting to set power above 0% after copying a material profile from a different machine.

Step 5: Interlock Circuit & Safety Switches

Boss Laser machines have multiple interlocks: lid switch, door switch, emergency stop, and sometimes water level. When any interlock is open, the machine won't fire (by design). But these switches can fail mechanically or the wiring can chafe over time.

Use your multimeter's continuity mode to trace the interlock chain. Start at the power supply's interlock input (usually two wires labeled IN1/IN2 or something similar). Short them temporarily with a jumper wire; if the laser fires, you've found your culprit. (Caution: leave the jumper in only for testing, and never bypass interlocks during actual operation.)

The mistake that cost me $450 plus a one-week delay: I assumed the lid switch was fine because the machine beeped when I opened it. But the beep was from a separate sensor — the actual interlock was a magnetic reed switch that had lost its magnet. (I really should have tested continuity first.)

Step 6: Focus & Lens Condition (The Overlooked)

I know, this seems unrelated to firing. But hear me out: a dirty or damaged lens can absorb so much energy that the beam is blocked completely, making it appear as if the laser isn't firing. CO2 lenses are typically ZnSe (zinc selenide); if they get a thermal crack, they can become opaque at 10.6μm wavelength. You won't see the crack with your eyes — you need a lens inspection tool or simply replace it.

Also check focus: if the lens is way out of focus (like 10mm too high), the spot size becomes huge and the energy density drops below the threshold for any effect. I've had three occasions where a customer swore their laser was dead, but a simple focus adjustment fixed it. (This is especially common when switching between wood and metal marking — the thickness difference matters.)

When This Checklist Won't Help

This list is optimized for CO2 machines (common in Boss Laser's LS series) and fiber machines (their MF series for metal marking). If you're using a desktop diode laser like the Boss LS-1410, the troubleshooting steps differ — diode lasers rarely have interlock chains or coolant flow switches. I recommend watching their official video guide for those.

For metal marking specifically: if your fiber laser fires but leaves no mark, the issue is usually wrong lens focal length or incorrect marking parameters (too fast, too low power, wrong frequency). I wrote a separate guide on Boss Laser MF-20 settings for stainless steel if that's your situation.

Finally, if you're shopping for a used Boss Laser, this checklist doubles as a pre-purchase inspection list. Run these six checks before handing over any money. It'll save you from buying a machine that looks fine but has hidden issues. (I've seen three buyers walk away after Step 1 revealed a blown PSU.)

Common Mistakes People Make After Reading This

• Replacing the tube first — do Steps 1-4 first. 80% of “dead tube” symptoms are really power supply or controller issues.
• Skipping the coolant check — especially if you topped off with tap water instead of distilled. Minerals build up and jam the flow switch.
• Forgetting to save your settings — after a firmware update (January 2025, at least) the Ruida controller may revert to default max power of 20%. Double-check before running a production job.
• Trusting the “last known good” file — I wasted a day re-engraving a rejected part using the same file that worked last week, only to realize the USB cable had partially failed during file transfer.

Bottom line: this checklist won't catch 100% of faults, but it'll catch the 90% that cost you time and money. Print it out, tape it to your machine, and the next time you see a blank laser pointer, you'll know exactly where to start looking.