Topeak Whitelite 1W LED Cycle torch-repair - Page 1
Forum section: electronics / repair

author: andypandyplod
author_rank: Contributor
timestamp: August 16, 2015, 01:10:16 pm
content: Hi,I am trying to repair a 'Topeak Whitelite 1W LED Cycle torch'which is powered by a 3.7 volt CR123 battery.I had to replace the Luxeon 1 watt LED.It works correctly at full brightness when connected to a 5v supply to the 3.5mm socket (allows a separate 5 volt battery to be connected).The push button allows Full on,Flashing and off.I found the 3 pin SMD device marked 015PB,(M1 on PCB),was open circuit.I have managed to get the torch to work by replacing it with a BC327 PNP transistor on short leads,because of its size.It appears the brightness is down 50%?.I cannot find any info on the faulty device,and wondered if it was a digital transistor,or a mosefet?I know there is a LD1117 3.3v output,used a constant current device,and a 5104A device used to boost the 3.7 volt battery to 5 volt. I have attached a PCB photo,and a circuit.Any ideas please?

author: mikerj
author_rank: Super Contributor
timestamp: August 17, 2015, 01:27:46 pm
content: The fact that the mystery component has an M prefix suggests it may well be a MOSFET.You might need to have another go at the schematic, I think there may be a few mistakes. The LED anode and what appears to be the supply pin of the microcontroller is connected to ground and the output of the switching regulator (cathode of D1) doesn't seem to be actually powering anything.The wiring around the micro and LD1117 looks odd as well. Could you post a picture of the bottom of the PCB?The switching regulator is possibly aGMT G5104, a 300mA boost converter. It's a bit odd that it's permanently being powered from the Li-ion cell with no way of switching it off though.

author: andypandyplod
author_rank: Contributor
timestamp: August 18, 2015, 04:44:22 am
content: Hi,thanks for taking an interest. I was puzzled by what I had drawn,but worked out there were two parts to the circuit. One was using a +5 volt separate battery to give longer operation of the LED.The other using a 3.7 volt li-on rechargeable battery. I did the circuit quite quickly, and at the time could not find the 5104 pinout details on the internet,so there was a bit of quess work.Thanks to your info I will have another go later today. I worked out,that inserting the 3.5mm +5 volt plug disconnected the battery -ve,and supplied +5 volts to the L1117, 3.3 volt regulator. I have attached a photo of the rear of the PCB.

author: mikerj
author_rank: Super Contributor
timestamp: August 18, 2015, 02:51:07 pm
content: This is my best guess based on what I can see, since some traces are hidden in the pics and I can't see the resistor reference next to the wires. Pin 1 is the one closest to the edge of the PCB.The two resistors from the micro to the transistor gate/base are confusing however, so not 100% sure that is correct. I've drawn the transistor as a P channel MOSFET, I think that's more likely than a PNP.

author: andypandyplod
author_rank: Contributor
timestamp: August 18, 2015, 06:36:10 pm
content: Hi,thanks for drawing the circuit. By the way the mosfet is in the circuit do you think it will be a P channel one?.Any ideas of ones to try please?thanks again

author: mikerj
author_rank: Super Contributor
timestamp: August 19, 2015, 05:06:14 pm
content: Something like a Si2301DS should be ok.

author: andypandyplod
author_rank: Contributor
timestamp: August 22, 2015, 02:55:16 pm
content: Hi,thanks