# Unable to control laser % **URL:** \ **Category:** 🔥 Laser\ **Created:** [August 29, 2026, 10:12pm UTC](https://forum.sienci.com/t/unable-to-control-laser/27015 "2026-08-29T22:12:31Z")\ **Posts on this page:** 13\ **Page:** 1
**Author:** ![checkers](https://forum.sienci.com/letter_avatar_proxy/v4/letter/c/e0b2c6/32.png) [@checkers](https://forum.sienci.com/u/checkers)\ **Post date:** [August 29, 2026, 10:12pm UTC](https://forum.sienci.com/t/unable-to-control-laser/27015/1 "2026-08-29T22:12:31Z")
I have an Altmill 4x4, and am using Gsender 1.6.0 and I went through the Common laser issues post and Chrises video. The laser turns on and off properly but checking the voltage at the output of the SLB when test firing is always at 4.7 volts. I have changed both sliders (right under the laser test button under Spindle/Laser tab and in the center bottom of the screen). I am using the Jtech 64w laser ---
**Author:** ![gwilki](https://forum.sienci.com/user_avatar/forum.sienci.com/gwilki/32/366_2.png) [@gwilki](https://forum.sienci.com/u/gwilki)\ **Post date:** [August 30, 2026, 3:03pm UTC](https://forum.sienci.com/t/unable-to-control-laser/27015/2 "2026-08-30T15:03:27Z")
@checkers What is your $743 value? ---
**Author:** ![checkers](https://forum.sienci.com/letter_avatar_proxy/v4/letter/c/e0b2c6/32.png) [@checkers](https://forum.sienci.com/u/checkers)\ **Post date:** [August 30, 2026, 5:30pm UTC](https://forum.sienci.com/t/unable-to-control-laser/27015/3 "2026-08-30T17:30:42Z")
the $743 is set to 0 ---
**Author:** ![gwilki](https://forum.sienci.com/user_avatar/forum.sienci.com/gwilki/32/366_2.png) [@gwilki](https://forum.sienci.com/u/gwilki)\ **Post date:** [August 30, 2026, 5:33pm UTC](https://forum.sienci.com/t/unable-to-control-laser/27015/4 "2026-08-30T17:33:39Z")
@checkers I didn’t really think that it could be that easy. 😀 So, when you send a command to run at 50% power or 25% power, the output remains the same, yes? If so, how are you sending the commands? Has it ever worked properly? ---
**Author:** ![Jens](https://forum.sienci.com/letter_avatar_proxy/v4/letter/j/d2c977/32.png) [@Jens](https://forum.sienci.com/u/Jens)\ **Post date:** [August 30, 2026, 5:38pm UTC](https://forum.sienci.com/t/unable-to-control-laser/27015/5 "2026-08-30T17:38:52Z")
Just curious … is the output actually zero when the laser is off? A lot of stuff is switched on the ground side rather than on the high side … ---
**Author:** ![checkers](https://forum.sienci.com/letter_avatar_proxy/v4/letter/c/e0b2c6/32.png) [@checkers](https://forum.sienci.com/u/checkers)\ **Post date:** [August 30, 2026, 5:40pm UTC](https://forum.sienci.com/t/unable-to-control-laser/27015/6 "2026-08-30T17:40:03Z")
that is correct, regardless of power setting i am getting 4.7v when the laser is commanded on. i tried adjusting the power with the slider under the test fire button and the slider in the bottom middle of the screen. no this is a new setup it has always run this way ---
**Author:** ![checkers](https://forum.sienci.com/letter_avatar_proxy/v4/letter/c/e0b2c6/32.png) [@checkers](https://forum.sienci.com/u/checkers)\ **Post date:** [August 30, 2026, 5:41pm UTC](https://forum.sienci.com/t/unable-to-control-laser/27015/7 "2026-08-30T17:41:27Z")
it is at zero when off, the on off is working correctly just the power % is not responding to changes ---
**Author:** ![gwilki](https://forum.sienci.com/user_avatar/forum.sienci.com/gwilki/32/366_2.png) [@gwilki](https://forum.sienci.com/u/gwilki)\ **Post date:** [August 30, 2026, 7:47pm UTC](https://forum.sienci.com/t/unable-to-control-laser/27015/8 "2026-08-30T19:47:46Z")
@checkers How are you sending the % power commands? Are you just using the sliders? Have you tried sending commands using the console? Here is a link to an excellent “tutorial” from Paul Larsen on how to measure PWM output. > [@Laser function in a LongMill](https://forum.sienci.com/t/laser-function-in-a-longmill/1436/41): > > @Kyfe and @gwilki, you can check the output by measuring its voltage with a multimeter. You will get different results if you measure DC vs AC, but you can still tell. The output is a PWM signal (Pulse Width Modulation). The signal ranges from about 0V to 5V. Off would be 0V and full on would be a steady voltage close to 5V. For intensities in between the signal will be a series of pulses. At low intensities the pulses will be more off than on (lower duty cycle) and at higher intensities the … If you have not tried testing power this way, you may want to. ---
**Author:** ![checkers](https://forum.sienci.com/letter_avatar_proxy/v4/letter/c/e0b2c6/32.png) [@checkers](https://forum.sienci.com/u/checkers)\ **Post date:** [August 30, 2026, 8:33pm UTC](https://forum.sienci.com/t/unable-to-control-laser/27015/9 "2026-08-30T20:33:47Z")
yes I was just using the sliders, just tried using the command prompt and that seems to work. if Icommand m3 s10 I get .78v, m3s50 is 2.68v, and m3s100 is 4.7v. but if I run a test of 3 blocks at 10, 50 and 100% it just goes full power the whole time. (I am using light burn software and exporting the gcode to use in gsender ) ---
**Author:** ![gwilki](https://forum.sienci.com/user_avatar/forum.sienci.com/gwilki/32/366_2.png) [@gwilki](https://forum.sienci.com/u/gwilki)\ **Post date:** [August 30, 2026, 8:49pm UTC](https://forum.sienci.com/t/unable-to-control-laser/27015/10 "2026-08-30T20:49:24Z")
@checkers OK, you seem to be making progress. In lightburn, what is your Smax value? In gSender, what is your $730 value? They must be the same generally either 255 or 1000. In the gcode that you export from lightburn, what is the laser on command - M3 or M4? What happens if you just run the file in LB, that is don’t export the code to gSender? ---
**Author:** ![checkers](https://forum.sienci.com/letter_avatar_proxy/v4/letter/c/e0b2c6/32.png) [@checkers](https://forum.sienci.com/u/checkers)\ **Post date:** [August 30, 2026, 9:30pm UTC](https://forum.sienci.com/t/unable-to-control-laser/27015/11 "2026-08-30T21:30:15Z")
That seems to have done the trick! my Smax values were different I set them both to 1000 and now the intensity is changing as the program runs. i think my gcode is using M4 as a laser on, I am not very fluent yet but there is an M4 near the top but no M3 in the code. is that significant? thank you for all the help! ---
**Author:** ![gwilki](https://forum.sienci.com/user_avatar/forum.sienci.com/gwilki/32/366_2.png) [@gwilki](https://forum.sienci.com/u/gwilki)\ **Post date:** [August 30, 2026, 10:48pm UTC](https://forum.sienci.com/t/unable-to-control-laser/27015/12 "2026-08-30T22:48:32Z")
@checkers I’m glad that you got thing worked out. As I understand it, we want to have M4 turning on the laser. M4 allows variable power settings. M3 does not. I stand to be corrected on that by those who know much more about this than I do. 😀 @paullarson is my guru on all things laser, so I take no credit for helping you fix this. Have fun with your laser. ---
**Author:** ![paullarson](https://forum.sienci.com/user_avatar/forum.sienci.com/paullarson/32/8543_2.png) [@paullarson](https://forum.sienci.com/u/paullarson)\ **Post date:** [August 31, 2026, 1:59am UTC](https://forum.sienci.com/t/unable-to-control-laser/27015/13 "2026-08-31T01:59:09Z")
You are to kind, Grant.