Open circuit Lux - fried LS driver?

[Ty_Bower]

I've got a factory second Arc LSH which I modded myself. I've added a second resistor to boost current to ~600 ma and swapped out the optics for a Fraen. I noticed while reassembling it that the torque from the optics tended to twist the Lux on the driver board.

The leads to the Lux weren't that great to begin with (maybe why it was a second?) and apparently one of them twisted enough to break. I foolishly applied power while the driver was open load - essentially no Lux in there to complete the circuit.

I've since replaced the faulty Lux with a good one, but she still won't light up. When I apply power, I get a very brief, faint pulse from the Lux. Then it shortly goes out again. If I disconnect power for a little while, it will repeat this.

I thought I read somewhere that the design of the LSH was such that applying power without a load on the driver would fry some component. I'm afraid I've done that now. Can anyone suggest a remedy?

Thanks in advance.

 

[LitFuse]

You cooked the converter most likey. The LT1618 chip needs to be replaced.

There should never be enough torque on the Lux to cause one of the leads to shear.

Peter

 

[Ty_Bower]

[ QUOTE ]
LitFuse said:
You cooked the converter most likey. The LT1618 chip needs to be replaced.

There should never be enough torque on the Lux to cause one of the leads to shear.

Peter

[/ QUOTE ]

Oh hell. I was afraid you'd say that. That's the one with eight tiny legs, right? How am I supposed to replace that? (Duh, with SMT soldering equipment, silly).

I was very surprised when the leads twisted off. As I tightened the retaining ring, I noted the beam went out of alignment. I found a pair of needle nose pliers in the holes in the back of the driver board could turn it back into place. I fiddled with the alignment for a long time until the beam started to look good, then it went out. I twisted it slightly back, and it came back on. Lucky, I guess. This actually happened to me a couple times before I caught on to what I was doing.

After I realized I was shearing the Lux off, I took it back apart and tried to beef up what was left of the leads with a little solder. It worked well enough for about half a year (I wasn't so picky about getting it aligned "just right").

Then a couple days ago, I turned it on and got the short pulse of light. I guess I must have dropped it too hard, or maybe the force of the battery pack shifted it again. I took it apart, checked the Lux leads, and found that it would still light up (full brightness) while it was apart. Put it back together, and it was bust again. Took it apart once more, and now it's completely broken. /ubbthreads/images/graemlins/frown.gif

I replaced the Lux, but it's still no good. Can anybody solder in a 1618 for me?

 

[mahoney]

Been there, done that, ... almost exactly that

If you just want to send it out for fixxing, there's lots of modders on the board who can help you.

If you have a small soldering iron, you can replace the chip yourself. Linear Technologies was very kind about sending some "samples" of the chip to me. I found contact info in the CFP archives as well as the secret to doing the repair without SMT gear, desoldering braid.

Carefully note the orientation of the old chip on the board and remove it. (did I mention carefully noting...?) Clamp the new chip in place lined up with it's pads, I used a "whittled-down" clothespin. Use your small but still comparatively huge soldering iron to solder all the pins on one side of the chip in place and then do the other side. Despite any effort to use a minimum of solder while doing this, there is no doubt now a blob of solder covering all the pins on each side of the chip. Take a well fluxxed piece of desoldering braid and lay it over the pins and heat it with your soldering iron. Remove the braid when you see the solder wick into it. Inspect with a magnifing glass to insure that all the excess solder is removed. This trick worked fairly well for me, it took a couple of tries, but at the time, there wasn't quite the well developed network of LS service stations that there is now so I didn't have much to lose by trying it myself.

Remember, you can always grind or file a soldering iron tip to a smaller size. Just re-tin it before use, if your flux isn't strong enough, get a sal amoniac "tinning block" at the electronics store.

 

[markdi]

or wrap some skinny wire around the tip of your iron
and use the wire as a tip adaptor.

I read this some where - I have not tried this method

 

[kaseri]

I don't want to step on anyones toes here. Just an FYI.. Wayne from the Shoppe should be able to solder a replacement chip on that board for you. If I'm not mistaken he has some soldering gear made just for soldering items like that.

 

[cgpeanut]

Ty,

It can be done, you will need a plastic vise, radio shack heat sink clip, soldering paste and a fine tip soldering iron.

You can also get the LT1618 from digikey I think they are 5 bucks a piece I have some.

Once the LT1618 is removed flux the pads on the board, use the heat sink clip to hold and position the LT1618 the solder.

Be extra carefull removing the chip because you may remove circuit traces aswell /ubbthreads/images/graemlins/frown.gif use a combination of solder wick and solder sucker to remove all the solder from the pads before prying the chip off.

I've used this product to repair damaged circuit traces.

CircuitWriter: