Laser is not turning off, ALways high... sorry for the repeat of topic

[Letchy]

Hi All

So my laser will not turn off, stays on high as soon as I hit the power button to let the 12v into the system. I know you have heard this a thousand times and I tried to search and read all the other posts but they still didn't fix my issue so here we are.

First up:
No clue where the machine was originally brought, its an Eleks laser though. The laser/machine did originally use to work as intended. The weak button works as intended when pressed.

The control board is not a standard one. See attached images, there is no jumper under the Arduino, maybe there is space for one? There are some random 3 pads underneath but no silkscreen to say what they do (refer to pictures).


What I have tried:
1. Benbox and its LT.hex (2 different sources) - I could not control the laser through their interface
2. T2laser and its default firmware and the GBL 1.1e Non-PWM one, also tried post-processing to D12 as well - All would not let me control the laser through the interface.

Is something blown? am I missing something? Is there a sure way I can test if it works and narrow it down? I assume the signal from the Arduino is not telling one of the ports to go to 0? as the laser I would assume (2 wire) would just be binary?

I do not have an oscilloscope to trial but I do have a multimeter but that doesn't help me with signals. 



 

[Zax]

The most likely cause is the MOSFET has shorted, simple answer is you need a new controller board.

The newer boards are designed for a TTL laser so the port has constant 12VDC and a TTL/PWM signal. As you have an older laser you would need to use the "motor" output port as that's the same as your current boards laser ouput, a 12VDC PWM switched output from the MOSFET.

https://www.banggood.com/EleksMaker-ManaSE-2-Axis-Stepper-Motor-Driver-Controller-Board-For-DIY-Laser-Engraver-p-1015557.html?rmmds=search&cur_warehouse=USA

You can find others on Aliexpress which are the older design if you prefer (just an example, there are literally hundreds).

https://www.aliexpress.com/item/32998500445.html

[Letchy]

Hi Zax

Thank you for responding, probably the likely cause.

I shall look at getting a new board but was wondering, can you point me to where the MOSFET is on the board? can I just replace it?

[ggallant571]

It is the relatively large IC with 3-pins and a tab. Pin 2 is internally connected to the tab and may be cut off. I would physically cut the remaining two pins before trying to unsolder the body and try to read the the part ID prior to applying destructive heat. Elsewhere on this site I posted a reversed enginered schematic of an earlier L7 controller board that has my guess of the major components.

[Letchy]

Cheers,

Is there a way I can test if the MOSFET is actually blown before replacing it? Sadly don't have an oscilloscope

[Zax]

Most boards have an IR7843 or equivalent MOSFET, picture for reference and datasheet attached.

I agree with ggallant571, snip the leads and then removed individually to prevent damaging the thru-holes.

[ggallant571]

Do you have a 2 or 3 wire connection to the laser?
Is the "weak" laser button on the controller or diode module?

You could create a dummy load with a resistor. The MOSFET should be capable of switching 3 amps so a 100 ohm at 12 volts should be very safe. Then use a terminal emulator or low level grbl command utility to issue gcode. The laser enable/disable commands are M03 & M05 while the laser power (PWM) is Sxxxx where 0 is OFF and 255 is full ON. With the laser OFF you should measure 12V at the MOSFET pin 2 and close to 0V when it is fully on.

[Letchy]

Thank you both for responding,

I have a 2 wire Laser and the weak button is on the diode module.

What size resistor are you suggesting for the dummy load? I assume I will be placing it between 2 of the terminals on the MOSFET? I could be completely wrong there.

I'll see if I have a replacement MOSFET lying around.

[Letchy]

So I had a look at the MOSFET and it says "FUO24N, IR217A, 16 03"

If I google that it does not bring up the MOSFET 

FUO24N brings up a IC's and MOSFETs but it is of a different Number (2N7000), Does that matter?

What is a suitable replacement for this part? Would an IR7843 be fine?

Cheers

[ggallant571]

Do you have an Ohm meter? This part is typically located close to the power jack and laser header. Can you post a picture of the board?

[Zax]

I would replace the controller, that is a very old design.

https://benboxlaser.us/index.php?topic=780.0

[Letchy]

I have ordered a new board but it might take a while given this virus and I live in Australia.


Hence why I was wondering if I could hack something together to make the laser work. I have attached images of the MOSFET and there are pictures of the overall board in my original post in this thread.

[Zax]

If you get a suitable replacement MOSFET you can replace it. I believe it's an N-channel MOSFET, but you will need to trace the connections or use a meter to determine pin out.

[Letchy]

Let’s give that a go. Would you happen to know all the suitable MOSFETs that I could use are?

I can’t find the datasheet or any specs on the current one on the board. Would you know the rating and specs of what MOSFET is currently on it? Pictures above.

Thanks for all the help, look forward to your response so I can get this done

[Zax]

Just use one of the electronics lookups for a replacement, or you could buy the exact same MOSFET as it's still available.

https://www.infineon.com/cms/en/product/power/mosfet/12v-300v-n-channel-power-mosfet/irfu024n/