It gets dimmer and a bit unstable below roughly 1.25 volts a cell, so it wont give full power over the entire span of the NiMHs. It still gives a nice green dot, but not nearly as poweful - i estimate below 10 mW.

I very much doubt the IR is doing any work here... i had one of these units cooled so it wouldn't produce any green, and i could see the (808 nm) IR come out as a dull red. The IR is not focussed like the green is, comes out in a pattern a few degrees wide not unlike a flashlight.

Also, i hooked up both the failing DX20 and the good DX30 to shunt connected to a scope today.

The bad DX20 actually has very steady current draw (270 mA or so), but optically the beam goes from bright to very dim in a second or two. The electric circuit seems to play no part in this whatsoever. I'm about ready to sac this laser and drive the pump diode at various currents directly just to see what happens.

The good DX30 shows current that drops off after a few seconds when ran off too low a voltage (somewhat depleted NiMH's). From sufficient voltage, it draws around 300 mA steadily, on the depleted cells it draws 280 mA or so to start with dropping off to 240. The difference in output light is bigger then you'd expect for such a small drop in current, but we are dealing with nonlinear optics here.

Thanks for the great info ben.
I always found it strange that my nimh don't last as long on my lasers as they do on other stuff. Irritates the hell out of me that I can't fully discharge it bofore having to recharge it.

So I guess you've sort of ruled out the current as a cause of dimming if I read correctly. The problem must be in the mca crystals then or the pump diode itself.

In case of the dud DX20, i'm quite conviced that something is wrong in the crystal asssembly, or at least in it being able to accept IR from the pump properly. It might also be mechanical misalignment, but i have to way to diagnose or cure such problems...

As the unit is pretty worthless right now, I'll probably just drive the pump at 300 mA from a current source to see what happens. Chances i'll just blow it up are quite real, but i want to make certain that its just operating just on the lower edge of the KTP's power range.

Since the feedback isn't used at all, i'm fairly certain a good unit should work on a steady current source, but i have no idea what the current for good operation is, nor am i sure the pump diode is still working properly. The latter i can perhaps verify after total disassembly.

A progress report...

I removed the existing driver board, and hooked the LD straight to a current source to get some more information, with reasonable results too.

First of all, i tried pump current vs green output. There is no green up to 200 mA, it gets really visible around 250, and it peaks around 300 mA. With this sort-of defective DX20, i doubt the output was up to spec even at 300 mA.. but the amount of light procuded was usuable no less. Voltage accross the LD measured 2.05 volts at 300 mA.

I produced to build a driver that could give it 300 mA with some regulation from 2 AAA's, which isnt an easy feat since there is only about 0.4 volt to work with (from full NiMHs). I devised a crude current control circuit, and managed to sort of fit it into the casing (see pictures).

The board was a bit longer than the original, but i managed to fit it in, though the endcap can't be pressed on well. I fixed that with some tape for now, electrical contact is okay between laser unit and tube.

End result: It still starts with a bright flash and ten dims, but not as bad as it used to. In fact, its quite a usable pointer right now, up to par with any 5 mW.

Some sidenotes:

- This mod isnt worthwhile moneywise, its a lot of work and results are not top notch. I did it to just see if i could.

- The current source provided here is a BAD design. It relies on a drop of a specfic LED and set of transistors, and current still rises with voltage. It works here, but building it is at your own risk entirely.

Also, i don't know if i'm overdriving the pump, and if so to what degree. I'll play with it a couple of times and let you know if/when it poops out.

Attached Thumbnails

 

I finally got my return back. If you remember, I told them to test this next one before they send it out. I got an email 3-4 weeks ago that said they were having a problem with QC. Anyways, I got this one yesterday and it seems good so far. I was 60 degrees this morning and the dot was really dim but I held it for a while and once it warmed up it seemed good again. I think I got the older one with the bigger hole?

I can smoke electrical tape slowly, won't light a sharpied match and I can feel a very light sting when I put it on my skin. Having tried a balloon because I don't have one.

I got my DX True30 about 2 weeks ago. Other than the switch becoming more "rattly" with time, I've noticed only a slight drop in light output over time.. I've been assuming it's due to batteries weakening.

First day out of the box with the batteries new, it popped a sharpied balloon at about 2' no problems. Now with 2 week old batteries (pretty light use) it's still quite visible in a darkened room and very visible at night.

The metal part you press pushes against the switch on the PCB. You may find with pressing the button, over time, the PCB gets bent away with the pressure, this allows the metal part to rattle more...It may be worth trying a non conductive packer behind the PCB to support it.

Regards rog8811

On some models, there is a little plastic spacer on the other side of the circuit board, preventing it from getting pressed in or bent.

I've been following this post for a while now as I waited for my True DX 30 to arrive. I'd convinced myself that I'd a 50% chance of getting a pile of crap - the button would give up or that it would dim to nothing after a couple of minutes.

Well it turned up today and I'm really impressed. Solid feel. positive action on the button and dazzling beam from the supplied no-name alkalines. Beam seems well collimated and no sign of dimming after about 5mins continuous use. Doesn't seem to vary as it gets warm through hand holding. Haven't tried popping but it wrinkles a black bin liner pretty instantly from a few inches. I'll wait till these supplied alkalines give up and then try it with some other batteries. I paid about UK £10 for this with free shipping so even if it does give up any time soon its been worth it because now I know what to expect *when I order my Nova 85 ! *

Update - it pops prepped balloons almost instantly from a few inches!

Are they sure this is only >30mW ???

my 35mw WL pops sharpied balloons quite easily, they're probably right on spec

I bought one too and the same thing happens T_T :'(

well, some positive feedback here:

Got mine about a week ago, and man, that thing kicks A55!!!
Beam is quite visible indoors, and when it's getting twilighty, outdoors produces a nice beam, too.
Man, that thing is so strong! Either mine is overpowering, my friend's DL 125mW is underpowering, or it's just really dusty at our house (or any combination of the three).

Now, more to some facts: I used it quite a lot the first days, shining at whatever I could, and soon output started to flicker, i.e. start full power, decrease in two steps to (guessed) 30% in about 1-1.5 seconds, or start off weak, and "fade" to full power. Sometimes it helped to just continuously click on-off-on-off...until it was working normally again, sometimes it helped to unscrew the battery case a bit (1/2 turn), screw back on, maybe repeated two, three times.
But after longer use, it just was "no more fun", so I had to change the batteries. Worked like a spell then again. Now I use rechargeable NiMHs @ 700mAh, these are really fine, and last about two days (that is, two days of playing around, maybe 30min of lighting) before it starts to noticeably fluctuate/dim again. I put mine into the charger every evening i have used it, so it's always fresh and nice.


An interesting thing was that at first, the beam was a bright dot with some zoneplaty pattern to one side, i.e. next to the spot was a 60°-segment with three segments of a circle . But now for some reason it's gone, and now I just have a "fat blob" around the dot.
Concerning that, the laser has quite a large aureole or corona, whatever you call it, around the dot. Its diameter is about 30 times spot diameter, and its intensity decreases something like a 1/r - function (no idea what that lokks like, but that's how I picture it in my head at least ).
I think ist is fairly large, but then again I don't know what the DPSS standards are here and for 26$ I can't complain.

Another odd thing is that the beam is gay, in the sense that it does not go straight forward, but instead at an angloe to the central axis of the pen (maybe 15°, so noticeable).


To sum it all up, those were some nice 26$, although I seriously need to get goggles now! My battery charger has green LEDs indicating charging is complete, but they are two-colored LEDs and the green seems to consist of green and red/orange. Now several times now when I stopped playing with my laser, my "parts in eyes responsible for seeing green light" were so saturated, that the LEDs appeared to shine orange, although I knew they were green...get goggles!!!




Is that spam filter abuse? I wanted to type "beam is not straight", but then it occured to me that the forum spam filter makes g-a-y to "not straight". so I typed beam is g-a-y. Is that an abuse now???

Just got a shipping confirmation, only took them 5 days too!

I'll keep you posted on the quality of my true DX