AlgoLaser 20W Driver Board Issue: Lost PWM Signal & Floating Gate

Community Laser Talk
1

Hi everyone,

I’m dealing with a frustrating hardware issue on my AlgoLaser Alpha MK2 20W, and after some deep multimeter troubleshooting, I’d love to get some opinions from the hardware gurus here.

The Symptoms: The laser suddenly stopped firing. The machine moves perfectly along the X/Y axes during a LightBurn job, but no beam is emitted. Additionally, the tiny blue indicator LED on the laser module’s internal driver board (LD_DRIVER_V1.2) is dead. There are no visible burn marks, melted traces, or smells on the PCB (silent failure).

Troubleshooting Steps Taken:

  1. Mainboard & Cables: Tested the mainboard output. It is sending a healthy PWM signal (scaling from roughly 1.5V to ~5V depending on the power percentage set in LightBurn). The wiring to the laser head is perfectly intact.
  2. Laser Diode: Tested the actual laser diode component inside the housing; it is not shorted out.
  3. The Driver Board (The Culprit): I traced the 24V main power all the way to the MOSFET’s drain. However, the gate is receiving 0V. The PWM signal is successfully reaching the input pad of the driver board, but it’s getting lost somewhere along the traces/SMD components before reaching the MOSFET gate.

The “Floating Gate” Confirmation: Here is the interesting part: I sprayed some electrical contact cleaner on the board’s logic section. The sudden thermal/chemical change temporarily bridged the micro-break. I hit “Frame” in LightBurn, and the laser successfully fired! BUT, when the frame ended, the laser stayed on.

This heavily points to a burnt/failed SMD pull-down resistor (or gate driver IC) on the board. The gate opens when it temporarily gets the signal, but since the pull-down circuit is dead, the voltage can’t discharge to ground, leaving the MOSFET locked open (floating gate).

My Question to the Community: Since sourcing just this internal replacement driver board from the manufacturer is difficult in my region, I’m considering two options:

  1. The Bypass Surgery: Adding an external 10k Ohm pull-down resistor between the MOSFET’s Gate and Source (GND), and running a jumper wire directly from the PWM input pad to the Gate, effectively bypassing the dead logic section of the PCB.
  2. Generic Replacement: Buying a generic generic 24V PWM diode laser driver board online and simply adapting the input/output wires.

Has anyone successfully done a manual bypass/pull-down mod on these specific 24V drivers? Or is the internal circuitry too complex (current limiting, etc.) to safely bypass directly to the MOSFET?

Thanks in advance for any advice!

2

More likely, it’s a cold solder joint that fractured when it heated up.

Here’s one three on an Arduino knockoff board:

If you’re a dab hand with a soldering iron, touch all the parts to resolder their connections. I’d start with MOSFET you’ve identified and work toward the inputs, but you get the idea.

Protip: You may safely assume the first bad joint you find won’t be the only bad joint. :grin:

1 Like
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I guess the engineers didn’t know they needed that other work they did. They didn’t really need that circuitry?

Can you explain why that section failed and what that circuitry does? Why would it be there if you could just bypass it?

Why don’t you just replace the component that failed?

:grinning_cat: