Slight output at 0V modulation on 500mW CNI MGL-H (WL203)

[m0f]

I've had these lasers for awhile and always have had a problem with them not shutting off all the way. When an physically connected to an FB3 dac (most likely any dac) with no cue loaded and output disabled I get a low powered beam from the greens.

It's in the area of 5mW and I've been working around it by aiming the zero point of the scanners into a zone I'm not using and using a beam stop to hide the output. But is a pain as I need to constantly adjust the scanners depending depending on the venue so that the center point / rest point of the scanners is in line with by beam block / beam stop.

Now with the dac completely disconnected, I get no output, but once physically connected it appears. Is there any way to fix this ? Could it be as simple as adjusting the 0-bias ? Will doing so have any potential negative consequences on the life of the pump diode ?

What are the other options ? Would adding a buffer circuit to the input either 1:1 or a via a colour correction board solve the problem ?

It acts in a similar way to a blue ld without a beam suppression driver, but the strange thing is when the dac is physically disconnected it does turn off. Though the dac should be outputting 0V, it seems there is some kind of signal present causing the green to output just slightly.

Could it be bad regulation of the green power supply, messing with the 0V reference point ? It is the wl203 style driver with power brick style power supply.

[dnar]

Its unusual for greens to bleed. Check your grounding, measure the mod signal pair at the driver, is it really 0V?

A small freak of the bias should suffice, but beware it could effect your modulation curve and timing. If your design includes a DZ color correction board then the "offset" trimmer will also give what you need.

[RGbee]

You could take a look at the minimum voltage' setting in your projector settings in QS (if that's what you are using).

[dnar]

You could take a look at the minimum voltage' setting in your projector settings in QS (if that's what you are using).

That won't help, it sets the minimum level during scanning only, not at idle.

[m0f]

Thanks for the advice. I ended up lowering the 0-bias a little bit which took care of it. One side effect I notice is that the ktp isn't quite as ready to go upon launching a cue. The resulting white is a tad more purple for the first few seconds until the green warms up.

I can deal with that, though I'm hoping it won't have any side effects such as cracking one of the crystals from sudden temperature differential. I'm happy to finally get rid of the green streaks I used to get when a cue was scanning but brightness at 0, and of course the static 5mW beam when the scanners were centered.

One big problem with these greens is modulation is not great at the lower power levels, below 25-30% or so they pulse on and off so a solid line appears line a dotted line (jelly beaning ?), they've done it from day one and was rather disappointed with them when I first bought them, but got used to working around it to a degree. As I haven't heard many complaints about CNI's in general I'm wondering if it's just this particular low power / low cost model. It sure kept me from giving CNI another chance as all my later purchases were DHOM because of this (and very happy with them).

I've always wondered if it's something that could be tec tuned to improve the situation but have always sort of depended on these for ongoing gigs. Now that I have the 10W's as a backup, I might look into trying to give these a tune.

[mixedgas]

Try a 560 ohm resistor to ground on the input. You may have needed some current sinking.

Steve