Some series of Wouxun chargers have the tendency to fail faster than you can blink your eyes. OK, I’m exaggerating a bit here, but the number of defective chargers is way higher than simple statistics could ever explain. Sometimes it’s just the 12V 1000mA switching power supply that gave up, but in most cases you will have to open up the charger.
A week ago I got one of these infamous chargers from a fellow HAM. A quick look at the circuitry explained a lot. Someone at Wouxun apparently tried to cut costs at the expense of reliability. One PNP transistor, the 2SB546 (or equivalent), can run a bit hot. On the PCB you can see that the designer made room for a heat sink, but somehow that 10 cent part never made it into the production process.
Three other components are missing too: a 56μH inductor (brutally bypassed by a piece of wire), and two capacitors. These parts are not essential for the reliability, nor for the charging process, but designed to kill most of the RFI the charger produces. Unfortunately I didn’t have these components in stock, but I will fix this later. First things first.
I picked up a few NEC 2SB546A transistors in a TO-220 package, added a small heat sink to one of them, and replaced the original one. A bit of thermal grease was applied too. Total costs: about $1. Don’t worry about the height, nor the 2mm the heat sink sticks out of the PCB – there’s plenty of room in the plastic case. The charger works great again, and now I have a nice spare on my desk.