Help fix a dead Small Sun ZY-777!

[kosmarnik]

Hi!

Preamble:
Got this thin 3xAAA light from DX, and would you believe it was DOA. Never mind that now. After siting in the closet for a year I decided to try to revive the little fella and learn more about flashlights fixing/maintenance.

Problem:
The problem is that it just doesn't turn on.
The tail switch is fine I checked and the switch works.
The led itself is also ok.
The driver in the head seem to be the problem, but it's out of my depth.


So I thought to turn to you for help This is THE place for all things flashlight.

I'd be grateful if you helped me diagnose and fix this.
I can do some light soldering and can poke my multimeter wherever you tell me to.


So here's the photo of the patient:



If you need more/better photos just ask.

PS: admins if this is the wrong forum for this kind of question, please move it to the right one. Sorry, I'm new here.

 

[qwertyydude]

If you've already tried to apply voltage to the center contact and ground ring and confirm it doesn't work then the only thing to do is buy a new driver board.

 

[kosmarnik]

If you've already tried to apply voltage to the center contact and ground ring and confirm it doesn't work then the only thing to do is buy a new driver board.

I have tried that, and no it doesn't work, Also if it did work, I would not be here asking
As there are only 4 components on the driver I would think that replacing one that is dead would be all the fixing it need to bring it back to life.

IDK, I'll try checking for continuity of every component later. Would that work?

 

[qwertyydude]

It really doesn't make sense to diagnose and repair these boards to the component level because it is kinda difficult to buy smd devices retail and by the time you do find one you've probably spent more money than a board because I never see anyone selling individual smd components. Not to mention soldering smd's is a pain in the butt.

Just measure the diameter and buy a new board from dx for 3-4 bucks and you can even upgrade to multi-mode or higher currents. If going for the higher current route it's a good idea to improve heatsinking.

 

[Illum]

c'mon guys, wheres the fun in buying a new driver when you can learn about the broken one?
Besides, this isn't exactly a light that requires urgent repair anyway

The driver your looking at has a couple cold solder joints, apply some new solder, swap out the wires, reflow the center bud, check to see if the inductor bobbin is damaged, use a multimeter to check if that diode still works, if not unsolder it and try on an 1N4148 signal diode available from radioshack.

When you bias the input with your power supply, is there any current pull?
Does it indicate a short?
Check the output pins with your multimeter set on ohms, is there resistance? if theres very low resistance between those wires in the absence of the LED the ceramic cap under the wires probably failed, again probably due to heat. If it failed use a 0.1uF ceramic cap and see if it works.

If the driver wobbles when seated, theres probably intermittent contact on the driver. No harm in adding some extra solder on the rim of the driver board. Any excess can be filed off and reflowed

Complete all the procedures I highlighted above, then report back on your findings

honestly though, its too much of a hassle to buy a single SOT-223 chip and pay the same amount of shipping that you'd pay if you were to buy 1000 SOT-223 chips. You'll have to then figure out a way to solder it back in if your iron was a general purpose iron and not one with a pencil tip specialized for SMTs...

What would I do with it? wipe the board, figure out a way to mount a ZSXC380 in the original drivers place and play with the existing inductor connected to the right places. If its between 22-100uH it will guarantee output of about 3.5V ~62-70ma at 3V input, no caps needed. Vin is good up to 6V, but being a step-up efficiency is max at 3V [95%], I'd remove the battery carrier, solder a wire between the contacts for one of the battery catches, and use the light like a 2AAA shower head LED light. If there was only a couple 5mm LEDs to begin with, I'd locate a high flux piranha LED, solder it in the LED board they have, center it on the reflector then superglue it in place. The drive current will go from up to 70ma [Vin = 3V, inductor = 100uH] and down to 20ma [Vin = 1V, inductor = 100uH]. Between then it'll be a screaming bright "5mm LED" light that runs on 2AAAs, if I really want to, its even 18500 Li-ion compatible :nana:

 

[kosmarnik]

c'mon guys, wheres the fun in buying a new driver when you can learn about the broken one?
Besides, this isn't exactly a light that requires urgent repair anyway

Exactly. This is supposed to be a learning process

The driver your looking at has a couple cold solder joints, apply some new solder, swap out the wires, reflow the center bud, check to see if the inductor bobbin is damaged, use a multimeter to check if that diode still works, if not unsolder it and try on an 1N4148 signal diode available from radioshack.

When you bias the input with your power supply, is there any current pull?
Does it indicate a short?
Check the output pins with your multimeter set on ohms, is there resistance? if theres very low resistance between those wires in the absence of the LED the ceramic cap under the wires probably failed, again probably due to heat. If it failed use a 0.1uF ceramic cap and see if it works.

If the driver wobbles when seated, theres probably intermittent contact on the driver. No harm in adding some extra solder on the rim of the driver board. Any excess can be filed off and reflowed

Complete all the procedures I highlighted above, then report back on your findings

Wow, thanks. I'll get some time over the weekend (too busy ATM) to check all that out.
BTW how does one check if an inductor widget?
I was poking the board with the meter set to continuity check and sometimes the LED would light up (weakly, but I guess that's ok as it's been powered by the meter). I guess I should have written down exactly what happened when I poked where, but I forogt. Oh, well I'll just do it again on weekend.


BTW if you have some links like, "LED drivers for dummies" or "Electronics for morons", I'd appreciate if you posted some. Really, ATM I suck at it. But I'd love to learn.

honestly though, its too much of a hassle to buy a single SOT-223 chip and pay the same amount of shipping that you'd pay if you were to buy 1000 SOT-223 chips. You'll have to then figure out a way to solder it back in if your iron was a general purpose iron and not one with a pencil tip specialized for SMTs...

OK, now I lost you Is there such a chip on this driver?

That reminds me, I got an a nice DFI x48 sli mobo (cost ~$280) that needs power inductors replaced. I searched and searched, but an individual just cannot buy these things, only in thousands it seems

 

[Illum]

well, use your fingers to gently pinch the top of the inductor, there shouldn't be any give to it. ferrite bobbins are like minature wire reels, the neck part of the reel is most fragile from lateral shock and some lights have in the past failed simply because the light got dropped.

Most SMT inductors are either low profile or epoxy conformed to resist such trauma but for your light it isn't.

SOT-223 is the package ID, its dimensions are as follows:
http://www.dl7avf.info/charts/outlines/sot223.gif
what appears to be an SOT-223 package might turn out to be a SOT-89...so one can never be too sure

There are many drivers like it, the most well known aboard the forum is the AMC7135 used by DX. And no, I do not think its a 7135 that resides on your board because they are LDO current sinking regulators, not a switcher IC, which would need the inductor and a diode...and probably the decoupling capacitor too...:shrug:

as for links...you know, I've been looking for the same thing for years

 

[^Gurthang]

Kos,

I can think of a possible source for driver info is the mfg's web site. Most have "application notes" PDFs w/ sample circuits w/ all voltages, currents, resistance, etc. LOTS of good info.

 

[Illum]

Kos,

I can think of a possible source for driver info is the mfg's web site. Most have "application notes" PDFs w/ sample circuits w/ all voltages, currents, resistance, etc. LOTS of good info.

If the light is from DX...dunno, might be worth a try but chances are generic lights dont have datasheets.
If I can just read the words on the chip I'd be able to guess on its manufacturer. Motorola, national, ON-semi, and fairchild are the ones most easily distinguished.

 

[^Gurthang]

IL,

Yep, my bad.... I meant the driver CHIP mfg.... a constant current driver design is WAY over my head.