Cordless drills are very convenient to use, removing the worry of power cord management. But the batteries that give them their independence from an extension cord is also their weak point, degrading faster than their mechanical parts. This Makita M651D cordless drill system dutifully served many years, but its nickel-cadmium (NiCad) batteries could no longer hold enough charge to last a work session. Replacement cartridges are available, but it was more cost effective to upgrade to more powerful and longer-lasting cordless drills with lithium-ion battery packs. Which was why this system was retired.
The least useful part of this system is the DC1414 charger, as it was precisely tuned to charge those out-of-fashion NiCad chemistry batteries. I’ll take it apart first.
The charger disassembled easily, no glues or anything annoying held it together. Which is a good thing, because in the lower right corner of the circuit board I see a fuse that requires disassembly to replace. I also see a dotted line across the middle of the board, likely marking separation between high and low voltage areas of this board. I see the logo for Tamura corporation, who Makita apparently subcontracted for this device.
The circuit board is a single-sided design, with through-hole components on the top side without copper traces. On the bottom we see a few surface-mount chips and copper traces, some quite wide for more power-carrying capacity. There is a notable gap across the middle, corresponding to high/low voltage divider line drawn on the other side.
Unusual shapes at several solder joints for high-voltage components caught my eye. In addition to the typical cone shape structure, these solder joints have a five-fingered extension from the base of their cone. Is this intentional or accidental? If intentional, what is their purpose? If accidental, what caused it to happen? I don’t know enough to make educated guesses. The plastic enclosure for this charger will go to landfill, and the circuit board will go to electronic recycle. I shift my attention to the M651D cordless drill itself.
New Screwdriver 
The finger-like protrusions around some solder pads help distribute the rather high current to the copper. The soldering material (tin), although of lower resistivity than copper but having much more thickness increases the cross section, this way the conductivity. So they are fully intentional.
LikeLike
Do you know the technical terminology I can use to search for more information about this? I’d like to learn about the tradeoffs involved relative to, say, a larger diameter copper circle versus these finger protrusions.
LikeLike
Studying the PCB I noticed another reason for the solder fingers. They add more mechanical strength and rigidity to the parts having higher mass.
LikeLike