Bad day for modding

Flashlight Modding and DIY Parts
1

I received a FT order today that included two of these drivers:
https://www.fasttech.com/products/1127404

They don't look as neat as on the pictures, pcb is green, quality of soldering not exactly top notch. Decided to build a dropin with one, but wanted to swap the thin wires for better ones (probably not needed at 1.4A, but you know, just because ;))

Alright, soldered wires onto the driver and the dropin went together as usual. Checked it with a DMM before firing it up and noticed I had a dead short between positive and negative battery connection. What?! Opened the dropin up again and found out that where I had soldered the red wire to the driver board, the insulation of the wire had cracked open and shorted against the pill. OK, so I desoldered the wire, snapped the end off and redid the connection.

Driver goes into pill, dropin goes into my P1 along with an xtar battery and... it lights up! Yee-haw! Pulled out my DMM again to check the tailcap current and it read.... 1.05A! Are you kidding me? One of the 7135s must have a bad connection... Opened the dropin again to have a look at the solder joints, but couldn't see anything bad. Reheated a few of the solder joints just to be sure, but still only 1.05A.

I decided to use the other driver, this time with the original wires, and that works fine. At least something.

Well, now I'm left with a driver that will most likely spend the rest of its days unloved in the parts bin. Currently I have not the nerve to harvest the 7135 chips to see if or which one is faulty, and I don't want to contact FT for a refund because it might have been me who killed the driver while soldering the wires.

Anyway, thanks for listening, I'm feeling better now :)

2

I didn’t check which driver is it, but are you sure your tailcap current is the same than your led current?

3

You don’t need to harvest the chips. Have you fine enough tips for your DMM and calm hands?
While driving the LED, clamp your negative probe to GND and measure on the VDD pins directly on every chip with the other one. (Should be close to battery voltage)
If that’s ok on every chip, measure directly between OUT and GND on every chip. There should be your battery voltage minus your LED forward voltage. If not, it should be the faulty one (either somehow disconnected or dead)

4

Thanks a lot Dave, think I'll try that tomorrow night when I had enough booze to calm my hands :bigsmile:

@totilde: It's a linear driver, so basically yes...