Leadlight clone still dimming slightly- suggestions?

[joniverson]

I have a silver Leadlight clone, but not exactly like a usual Leadlight. When I did the simple pot mod, there was a green glue holding the pot in place which broke loose when I turned the pot, but I thought continued to interfere so I removed the pot completely. Now, the laser starts off very bright, as before, but dims slightly after a couple of seconds. It's difficult to see the dimming, but it definitely happens and then levels off. Sometimes though, it will brighten back up and sometimes not. Is there any way I can get around this and have the laser more stable as when I first did the pot mod? The batteries, being lithiums, seem fine and I tested them in an identical laser and there was no dimming. The dimming is very slight and hard to notice unless looking at the beam at an angle (the beam becomes harder to see) or looking at a slightly dimming reflection from a light colored wall.

Thanks,
Jon

 

[Lew Fong]

I have a silver Leadlight clone, but not exactly like a usual Leadlight. When I did the simple pot mod, there was a green glue holding the pot in place which broke loose when I turned the pot, but I thought continued to interfere so I removed the pot completely. Now, the laser starts off very bright, as before, but dims slightly after a couple of seconds. It's difficult to see the dimming, but it definitely happens and then levels off. Sometimes though, it will brighten back up and sometimes not. Is there any way I can get around this and have the laser more stable as when I first did the pot mod? The batteries, being lithiums, seem fine and I tested them in an identical laser and there was no dimming. The dimming is very slight and hard to notice unless looking at the beam at an angle (the beam becomes harder to see) or looking at a slightly dimming reflection from a light colored wall.

Thanks,
Jon

Hi Jon,

The performance your getting is very good if the clone is non-APC'd, like other Leadlights are. Can you see if an APC window assembly is in place? It will be a black plastic housing that slips over the output end of the MCA with a few small wires running back to the PCB. If you have one, the issue becomes more complicated.

 

[joniverson]

Hello again Lew,

Thanks for the response. I can't remember the internal configuration of this dimming clone as each one I have has a different circuit. Once I reopen it, I'll let you know.

Jon

 

[Lew Fong]

I wouldn't take it apart again unless you are sure you want to risk it; I was just curious about the configuration. I don't own a 105 clone...but if I remember correctly I saw a thread about them elsewhere concerning APC circuits not found on the originals.

The bottom line is, there is always going to be some power instability with non-APC units, and APC'd units that are modified can partially defeat the APC circuit, making it less effective than it might be otherwise at keeping output power constant. If you turn the pot back down a little and regain some APC effectiveness, that could indicate that the circuit is regulating power better. I've seen a few APC'd Leadlights that have this property...once you go beyond a certain output power level, the APC circuit has difficulty regulating as well as it did at a lower setting. Basically, the circuit is not expecting the output to be so bright, and tries to throttle back right away, and hard. Normally, the idea of APC is to ramp-up as the unit gets hotter, smoothly compensating for the power lost as temperature increases. Turning up the power with the pot can even invert the power vs. temperature characteristic for some portions of the normal operating temp range, making effective APC unlikely.

Something else, too: If it is a non-APC laser, you might want to walk away from it for a while and be sure it is really cold (room temp) before checking for stability issues again, since during testing they can get overheated easily and will give the impression that they are operating strangely, when in fact they are just a bit too warm.

Cheers,
Lew