Thanks to CRX I managed to disassembly my Fairy. Not that it was hard, but I feared that removal of insulation would be hard to reverse and didn’t really touch the head for this reason.
The light is much simpler than I thought.
At the same time after I learned how mode switching works (it’s just a spring that shorts another path on the driver) I’m surprised it’s not just a single resistor or linear regulator for the low mode.
Now…
Aside from LED swap, is it possible to boost the output?
Sorry for low pic quality, I lack both the skills and the hardware…
ADDED:
This is unregulated driver, so if I swap a LED Vf affects output, right?
What currents are you measuring in high & low mode?
Should be roughly 14mA through the XP-G2 with the 3R6 - 3.6Ω and 510 - 51Ω in series. (54.6Ω)
Around 220mA draw with just the 3.6Ω resistor so changing that to a lower value should increase the high mode output with not too much effect on the lower output.
I think that makes sense but not 100% so experiment at your own risk
I swapped the LED to the target one (Luxeon V2) before measuring current and the result is as expected - the light doesn’t turn on.
During the process I had 2 issues:
both anode and cathode pads seem damaged, each accepts a generous amount of solder but only at about half of its surface. Did I strip them partially by removing a LED while it was too cold?
I touched the transistor and it moved a bit. I put it back where it was before.
Note: I speak about generous amount of solder but I wicked some of it before placing Luxeon V2, so it was probably not grossly excessive.
Optical inspection does not reveal any shorts but I can’t be sure with the optics that I have, the transistor terminals A and B might be shorted.
Can I apply continuity test of my DMM safely to check that?
What else should I check to learn what’s going on?
I don’t think I botched LED polarity. Cathode is -, right?
Hot air for a while, then grabbed the led with tweezers to see if it will go off. It did, I didn’t use anything I’d consider “force”.
I’ll try unsoldering the led later, maybe tomorrow.
Thanks CRX
Only today I got the energy to work on the light again.
So…I checked connections again.
It turned out that I soldered it OK but I misunderstood negative connection - it is not on the outer ring but on the pad next to 3R6 resistor.
So I put it in the pill - it worked. But it was loose. How did DQG keep it in place? Was the insulation ring enough to hold the parts together? As of now - it is not.
While screwing the pill into the body - it moved. And the 3-legged component fell off.
I took my iron and soldered it back, looks very ugly but OK, at least I didn’t blow it away with hot air.
So…it lights up. Thanks again CRX.
But it is a moonlight-special, very dim single mode. That’s not news - I modded a broken light because I was afraid that it wouldn’t survive my modding and I didn’t want to care too much. But now I would like to enjoy this warm Fairy….
Any hint on what would it take to repair it for good?
Also, the driver falls off as soon as gravity encourages it to do so. What would be the best way to keep it in place?
A little solder paste on the outer trace, insert into pill and use a jet lighter on & off to heat the side of the pill with components facing up and don’t cook it or blast the LED etc.
That’s what I do anyway.
A little too permanent for me. I thought about silicone glue…and that’s what I’ll probably end up doing. But only if I can fix the driver, otherwise it doesn’t really make sense.
Well, it’s only traces, pads, resistors, LED and that switching component so what did you break?
And remember that ground trace needs to connect securely to the pill so glue on that might not be the best.
You say it’s a switch?
OK, I think I understand how it works now.
Batt+ goes to 3.6 ohm resistor and then to the LED+.
Batt- and LED- there are 2 parallel paths. One is with 51 ohm switch the other is with a FET.
Once the FET gate gets power it reduces resistance by a lot.
I think I’ll be able to measure the circuit now.
I wonder why did DQG use a FET at all? Couldn’t it work with just 2 resistors in parallel, 55 ohm connecting the first pad to LED+ and 3.8 ohm connecting the second pad to the LED+?
Good point. Maybe I should get some conductive glue. I’ve heard that they tend to be quite fragile, unlike solder. Whether too fragile or just right…I’ll see.
There is no high-and-low, just a single mode.
Measured 0.5 mA at fresh start, quickly falling.
Checked cell voltage - 3V.
OK, let’s put it in the charger and in the meantime try a 26350 that I got at hand. 26 mA, too much to stare at the emitter.
I measured everything I knew how to measure. Importantly, I checked that gate gets continuity with the central pad.
I don’t know how to measure whether the FET is fine…I thought there might have been some short, so after optical inspection (which didn’t reveal any) I measured continuity. My DMM measures there is between all pairs of legs. Is that OK?…
I doubt it should have continuity between all the legs.
I don’t like messing with SMD’s, electronics etc, never have so don’t know much.
The way I see it, you should at least have the normal low mode when a cell is connected if the components are all ok, a partial short or fault in the 3 pin switching component sounds likely.
So you should have a direct path through the 3R6 - LED - 510 - Ground when the low mode outer cell side trace is energized.
Then when the centre pad is energized it causes the switch to connect the LED negative directly to the ground ring bypassing the 510 so only the 3R6 resistor is in play giving high mode.
So you’re getting the exact same very low output on high or low mode now?
I would remove the 3pin component and see if the normal low mode works as normal, I think it’s busted if you’re sure everything else is ok.
A2 is a small FET, I’ve stacked another before for better power or changed it out to a better one. I have seen these little three legged FET’s do up to like 5.7A off an 18650 before, so it could be a cell limitation more than anything,
And yes, you must maintain a solid ground or high mode is likely not going to work.
Edit: As I recall the original D80 driver used two of the little FET, I’ve built a lot of D80’s with our FET+1 drivers and had plenty of the stock driver to rob parts from…
I’m not sure but it could be to smooth the switch, prevent spikes?
It’s connected to the thermal pad and the 510 resistor (through the thermal pad) so it would appear to be for the low output side. I’m no electronics guru either so I can only surmise.
