Fixing a Kids’ Educational Toy

Alphabet training toy

A while back, my wife got this alphabet-training toy for one of our nephews. When they opened it and tried it, it “didn’t work and the batteries got hot.” Sounded like a short to me, so I figured I’d take a look.

Alphabet training toy, interior

The inside was interesting — I wasn’t expecting a bunch of little pushbutton circuit boards and a ton of fly wires (bundled together with cellophane tape), but I guess it makes sense. In China skilled labor is cheaper than automation, so a bunch of little boards with hand-soldered wires probably cost less than one big board made by a machine.

Alphabet training toy main circuit board

I put my meter across the terminals of the (empty) battery compartment and measured 0Ω — a dead short. I visually inspected every connection on the main PCB, assuming I’d find a solder bridge, but I didn’t. I desoldered the battery and power LED ground wires from the PCB (outlined in the white rectangle) so I could start isolating the short, and the short went away.

Let me say that again: I measured across the battery terminals (with the ground wire disconnected from the circuit) and got no short, as expected. I measured across the LED and got no short. I measured from the ground pad on the PCB to the positive terminal and got no short. I reattached the ground wires, still had no short, and the toy powered on and worked.

I’m quite certain I didn’t fix a solder bridge at the ground pad. My best guess is that while I was moving all the other wires to make room to work, I pulled apart something that was making contact and shouldn’t have been. But it’s quite a mystery what I really did that fixed it.

Except for the Batteries

Except for the batteries, which weren’t making reliable contact.

Kids' toy battery compartment

The shoulders of the cell compartments were too thick for the positive ends of several different brands of AA cells to make contact with their . .  uh, contacts. So I sharpened up my best $3 wood chisel (the one that I use to pry up leads on circuit boards I want to desolder) and shaved them down, and now the batteries make great contact.

But It’s Too Late

My wife says the nephew has outgrown the toy, so it won’t go to him. We have a couple of nieces about the right age, so one of them might get it, or she might take it to a thrift store.

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