$3 Multimeter Teardown

[Diode Gone Wild] and his cat decided to see how a $3 meter worked inside. The meter was marked as a DT-830B and he already had an older one of the same model, and he wondered how they could afford to sell it — including shipping — for $3. You can see a video of his testing, teardown, and reverse engineering below.

What was odd is that despite having the same model number, the size of the meter was a bit different. When he opened the case to install a battery, he noticed the board didn’t look like it had fuses or components appropriate for the rated voltages. He decided the missing parts might be under the board and tested the meter.

In all fairness, for $3, the meter agreed pretty well with his other meters. The AC scale appeared to be little more than a diode feeding the DC meter with some slightly different engineering unit conversion coefficients. Not the most accurate way, but certainly in line with what you’d expect from a $3 meter. Afterward, though, the case and PCB came out and there were no additional components on the other side of the board.

The original DT-830B had beefy resistors where it needed them and — most importantly — a fuse for the current measuring function. The new one had a marking on the case about the type of fuse it uses, but inside there was no fuse, even though there were PCB pads that could have been for a fuse.

Maybe those parts weren’t necessary? After sketching out the schematic, the video shows that in fact, the voltage and power dissipation really did require bigger components. In addition, a connection error could easily put very high voltages right to the IC.

This looked a lot like the DT-832 we saw a while back. That one had a fuse, though, and we aren’t sure if it had better-rated resistors or not. We’ve also seen cheap meters with fuses that weren’t actually used.