$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.

43 thoughts on “$3 Multimeter Teardown

    1. It holds surprisingly well, at even twice the rated voltage. Also the measurements don´t appears to be too much inaccurate, for that price.

      It just needs better test leads and a fuse to be more safe to use, well enough for any low-voltage work.

    2. Hmmm- I have almost the exact same multimeter – mines a model “DT830D”, and it’s orange, not black, with a nice orange rubber cover. Bought it at a supermarket about 15 years ago. for R60 (about US$4 in today’s money). It’s been on mains voltages (here in South Africa we have real mains of 220VAC), 10 Amps DC, and everything in between. Never batted an eyelid. And the continuity beeper is instant on, instant off, unlike my work Fluke, which has some kind of sampling delay which makes it useless for pulse counting

      1. I was surprised that he chose to place the test leads into the mains socket with his hands, instead of using something else to hold them in and using the switch on the outlet strip to send power to the DVM.

        I also wish he had put a “good” meter in parallel with the DVM under test during the HV tests to see if the DVM was reading accurately at those levels.

    1. LOL. But seriously cheap measuring means that that kind of functionality can be incorporated into other devices. Sort of the way practically every WiFi chip also has BT, even if never used.

        1. I don’t know about that particular meter, but a lot of the cheap DVM chips require they are isolated from the ground they are measuring. So a battery is perfect, but hooking them to a power supply won’t work. Some can and some can’t, but you’d have to figure that out.

        2. If you just care about volts and amperage, there are a few panel mount meters out there for this purpose on AliExpress and co. depending on the rating they cost about 1.5$
          https://www.aliexpress.com/item/Mini-Digital-Voltmeter-Ammeter-DC-100V-10A-Panel-Amp-Volt-Current-Meter-Tester-0-28-Blue/32824062417.html

          Or if you only care about voltage you can get some for 0.80$
          Much better deal and already in the perfect form factor for the purpose :)

      1. I bought a Midland 12 volt power supply last month at Habitat for Humanity’s Re-Store for a dollar.
        It has two panel mount fuse holders on rear cover. Before plugging it in, I pulled one of the fuses, only to find it wrapped in foil!
        The other fuse was the same way…

        … at this point, I haven’t bothered to investigate further.

        1. Probably it will work fine if you put a normal fuse without the foil. This is something CB’ers used to do since there is a myth that the voltage drop over the fuses will limit the radio range, so you cover it with something that conducts better…

    1. When I was in high school none of the Fluke meters we had in the electronics lab had the fuses installed for current measurement. The 2nd and 3rd year classes could use them to measure current if you asked the intructor for the fuses, but he got tired of the first year students putting them on current and plugging them directly into the wall outlet and frying stuff. First year if you wanted to measure current you had to measure the voltage drop across a shunt and use Ohm’s Law :-P

    1. I once discovered the hard way that the ‘el cheapo’ multimeter I’d just bought was labelled incorrectly. I needed to test mains power, so I put the leads in as labelled but it turned out that was the position for current rather than voltage, so I was just shorting the mains. Made a nice bang before the circuit breaker cut in.

    2. Have one sold under a different name but same model number and board. The only thing that doesn’t hold up against a decent battery are the wire used for the leads. Replaced that wire with Nichrome wire in silicone jacket and haven’t had a problem, seems to have boosted the accuracy of the meter a bit too. Wouldn’t let a kid use it before upgrading those lead wires, the junk they sell it with melts under loads the meter is rated to handle.

    1. With a coupon.
      I have like 4. the meters are fine, some batteries are dead but the leads keep breaking. Its cheaper to get the coupon, buy a 0.59 snap knife than to buy a battery.

      1. I think I have more than a dozen still in their blister packs. They disappeared from the local stores for a couple months this past summer. I thought maybe they had quit making them.
        I see newer ones have lower maximum AC ratings than older ones.

  1. I use to have a number of these, but that AC single diode nonsense put me off. That and the weak cables and probes. On ACV any DC level present is not only visible in the final reading, but is doubled. So 12v ac with 5v dc on it reads as 22vac in one direction and 2 vac in the other. If all you’re doing is measuring low voltage DC, in a pinch, it’s ok, perhaps leave one in your glove compartment, but for anything else, spending just a little more is worth it.

  2. A friend of mine used to collect the Hazard Fraught meters when they were freebies. He would teach basic Ohms Law/Watts Law to people and when they grasped the basic understanding, and could USE IT, he would give them a multimeter.

    We tested a bunch of these alongside our Fluke meters, and they were mostly dead on for most basic measurements.

  3. These things are sold all around Brazil, at prices from US$4 up to US$8 , and have been for a long time. I have owned a couple of them, and my only claim is about the crap leads (feels specially dangerous connecting it to mains power). Other than that, a good starter multimeter

  4. For your average low voltage electronics tinker these things are just fine. And are good for beginners considering how cheap they are if you have to pay for them at all. Your typical beginner will probably destroy a multimeter or two starting out, so why not destroy one of these cheap meters instead. Just stay away from mains voltage with them and you’ll be fine.

  5. Been using the cheap “CEN-TECH” s for a decade + now. Yez they been getting cheaper inside. Fuses. Haaaa ha ha. early ones did. Leads are freaking cheap but meter works and a neophyte fries it being a dumbass not an issue. Glass fuses cost more to replace in better DMM then these cost. Vast majority of fails is due to newbies in Amp measuring volts. Decent 9volt battery costs more than it. Much of which has been said already. Never had one ‘pop’ though. No problem to 500V anyway. Quiet death from goofy oops but far better than letting borrow expensive meters which may not survive stupidity.

  6. Good multi-meters have a separate jack for current measurements. Turning the dial on one of these cheapies whilst connected, or worse thinking that when it’s switched off it is immune to such dial twisting is the quickest way to trash ’em.

  7. I have lots of old meters. I used to assume that certification/testing laboratories like UL and CU would keep unsafe products off the market, and maybe they did at one time, but it seems that foreign manufacturers have learned that testing is expensive and extremely low prices and the power of the internet will sell their products much more quickly thereby turning quick profits without the hassle of testing. Private websites like the one in this post help fill the gaps and keep us informed, but usually not before the markets have already been well flooded with the cheap stuff.

    The good news is that I have recently seen some better quality meters come out of China that actually do try to meet CAT ratings, though maybe not always accurately. You do have to pay more, but with a bit of hunting, $50 can get you a good quality meter that is reasonably safe to use.

  8. I’ve purchased half a dozen of the El-Cheapo brand meters from a couple of sources. One thing that they all had in common: resistance measurement didn’t work at the low end (anything below 1 kohm). A few of them wouldn’t measure resistance at all. Which, unfortunately for me, was the main reason I bought them—a homemade starter*** for rocket motors should have a resistance of a couple of ohms.

    ***In the US, “igniters” and “electric matches” are BATFE-regulated items requiring a user/manufacturer permit. So I don’t make igniters, nosirree-bob. I make motor starters…

  9. This is very similar (though not quite exactly the same) as the $2.75 Kelvin 50LE that I did two youtube videos on before (3 if you count the time I tried adding wifi to it). People love to bash them, but they really can handle adverse conditions safely, and are surprisingly accurate.

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