World's cheapest multimeter teardown

[rolycat]

This was purchased out of idle curiosity during a discussion in another thread.

As mentioned there, this is the 'deluxe' DT-830D variant of the infamous DT-830B meter, and boasts a (scratchy) continuity buzzer.

The meter cost £1.95 including postage in the UK. It was sent via 2nd class 250g Royal Mail large letter post, which costs £1.17, and included a PP3 battery. The cheapest zinc chloride PP3 batteries I can find are 50p, so the multimeter itself effectively cost 28p, or about 40 cents US.

The (new and boxed) meter:

As you can see, this apparently boasts "new improved quality", which does make one wonder just how ghastly the old model must have been.

Because this is the rather horrible interior:


The only discernible input protection appears to be a 200mA glass fuse for the low current range.
The battery terminals have no polarity marking and the battery fits either way round...

[EDIT] Here is the backside of the beast, by popular request:


As is often the case, DC voltage reading on the meter was pretty accurate:


Since it would clearly be dangerous and irresponsible to use this meter for measuring anything higher than about 30V, I connected it to a 1000V power supply:


...which it seems to have survived.

Incidentally, the vendor sold eight of these in very short order after it was mentioned on this forum, and has now jacked the price up to £2.95.

[wraper]

Looking on the PCB, definitely this is not the cheapest one I have seen.

[rsjsouza]

Incidentally, the vendor sold eight of these in very short order after it was mentioned on this forum, and has now jacked the price up to £2.95.

Why wouldn't he? The meter withstands 1kv!

[rolycat]

Looking on the PCB, definitely this is not the cheapest one I have seen.

Cheapest in cost, not necessarily in quality. I know some shops give similar meters away, but you normally need to buy something else. Maybe it's possible to buy a new multimeter complete with battery for under a dollar somewhere in the world, but it seemed like an arresting title 

[paulie]

Arresting title yes, but I don't think this is actually "Worlds Cheapest" in cost or design. The freebies from harbor freight here have no beeper and many corners cut like no glass fuse or quality shunt. I also don't believe there is any way I could get one even for the new price of $4.40 or anything close to that.

[McBryce]

My father actually has the "not yet improved" version of this which he regularly uses to measure up to 240V. His version has a 9V battery clip on a flylead instead of those very questionable springs.

McBryce.

[PA0PBZ]

I wonder what would happen if you really tried to measure 10A for anything longer than a second. I don't like the path to the shunt, and the return path can only be guessed.

[rolycat]

I wonder what would happen if you really tried to measure 10A for anything longer than a second. I don't like the path to the shunt, and the return path can only be guessed.

It has just successfully swallowed 10A for around 10 seconds. I had the back off, and the shunt got pretty warm, but the reading was correct.

I was half expecting it to let the magic smoke out 

[rjardina]

Arresting title yes, but I don't think this is actually "Worlds Cheapest" in cost or design. The freebies from harbor freight here have no beeper and many corners cut like no glass fuse or quality shunt. I also don't believe there is any way I could get one even for the new price of $4.40 or anything close to that.

This is a coupon that I have now. I have seen some that are completely free. You do have to buy something, but they do sell 10 cent phillips #2 1/4 hex bits. And at my local HF they do allow printed coupons.

[Hydrawerk]

Hey, is that thick copper wire just lying on the PCB?

[Hydrawerk]

Note that solder joints that will not last long and a PTC replaced by a resistor.

[paulie]

This is a coupon that I have now. I have seen some that are completely free. You do have to buy something, but they do sell 10 cent phillips #2 1/4 hex bits. And at my local HF they do allow printed coupons.

As hard as it might be to believe I've acquired over 250 of those HF meters over the last 15 years starting with the black, then yellow, and finally current red ones. Most w/o any purchase necessary but they are tightening up due to inflation.

I guarantee those are not as good as the ones rolycat shows. HF "Centech" ($3 Ebay shipped) are a good deal and have that great on/off switch to cut dial wear but a beeper like in this threads is a priceless feature for my application. Usually available only on much higher cost units.

BTW It wasn't the shunt heating up but rather cheapo banana contacts. However the first thing to go in a high current short is always those low gauge leads. Melted insolation everywhere.. and that SMELL!

[rolycat]

Hey, is that thick copper wire just lying on the PCB?

Not quite.
I'd say there's nearly a millimeter between the wire and the board. For the guys who build these things I guess that's as good as a mile.

BTW It wasn't the shunt heating up but rather cheapo banana contacts. However the first thing to go in a high current short is always those low gauge leads. Melted insolation everywhere.. and that SMELL!

I suspect the first casualty would be the trace running from the 10A jack to the solder joint linking it to the main PCB. The shunt does get warm, but that gets toasty. The leads seem to have a decent amount of copper in them - resistance is around 0.1 ohms each; not far off the Fluke leads which are admittedly twice as long.

[PA0PBZ]

I suspect the first casualty would be the trace running from the 10A jack to the solder joint linking it to the main PCB. The shunt does get warm, but that gets toasty.

Did you find where it returns to the common jack? You probably have to lift the pcb for that but I can't see a lot of space for a decent track there.
Looking at the picture it must be the middle solder joint, but where it goes from there (both directions) is a mistery.

[rolycat]

I suspect the first casualty would be the trace running from the 10A jack to the solder joint linking it to the main PCB. The shunt does get warm, but that gets toasty.

Did you find where it returns to the common jack? You probably have to lift the pcb for that but I can't see a lot of space for a decent track there.
Looking at the picture it must be the middle solder joint, but where it goes from there (both directions) is a mistery.

PCB duly lifted and photographed - I've added the picture to the original post. The trace looks to be the same (inadequate) width as for the 10A jack. But hey - it works (just).

[meeder]

I think that I have the same thing somewhere around the house. It was sold in the Netherlands at the ALDI discount supermarket a number of years ago.

[Macbeth]

I think that I have the same thing somewhere around the house. It was sold in the Netherlands at the ALDI discount supermarket a number of years ago.

I don't recall ALDI (UK) selling the 830B's. I have a"Workzone" aka Mastech M92A from them. It's an altogether much higher class of meter - it even has a FLUKE YELLOW style rubber holster. I paid £7.99 IIRC with the ALDI 3 year warranty.

Why, it looks like our favourite Israeli seller is up to his usual ebay tricks. $50 + $25 P&P + $ import duties on a bashed up POS. It is working though and doesn't look like HAMAS have had their way with it, so it's not quite up to his usual rubbish. Oh wait... he does have a useless dead one for only $20+. I was beginning to lose faith in our Israeli surplus guy. 

Found a teardown and repair of an M92A here, in Hungarian.

[dannyf]

I have been the biggest fan of 830, using them since the 1980s. It is very difficult to get them to get inaccurate readings out of those guys.

Best buy for the money, especially when you get them for free.

[paulie]

I suspect the first casualty would be the trace running from the 10A jack to the solder joint linking it to the main PCB. The shunt does get warm, but that gets toasty. The leads seem to have a decent amount of copper in them - resistance is around 0.1 ohms each; not far off the Fluke leads which are admittedly twice as long.

So yours seems to be a little better than the HF version which has almost no copper in the leads. .5 ohm at Best. Several of the customers and friends I gave meters to ignored my warning and decided to measure amperage of their car battery by putting probes across or the like with expected result. In all cases it was the wires that went first. IMO those runs are more than adequate for 10a.

Anyway there's an improved DT830D version on Ebay ( http://www.ebay.com/itm/111512622657?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT ) with built-in signal generator for $5, I have 2 coming. Here's a REAL teardown of that model: http://www.petervis.com/meters/dt830d/dt830d-multimeter-circuit.html . It's multi-part article so check the other links at the end.

BTW is beeper response quick or slow? That is very important.

[miguelvp]

That meter looks a lot like the GB GDT-200A, at least from the outside:



Not that the inside looks much better:



What drives me nuts is that one of the two ball bearings always gets dislodged, and it's rattling inside. Tried many times to place both so they stay in place but one always tends to get loose, since the board is held by self tappers I don't want to over tighten them.

[rolycat]

BTW is beeper response quick or slow? That is very important.

It's pretty quick - faster than a Fluke 27, for example - but very scratchy and rather anaemic.

[Fungus]

I took a couple of them apart in one of my videos:



The plastic case on yours looks quite nice but the insides are awful. Those battery springs - shudder.

Still, you got a beeper, a fuse and a proper box. You can't really complain for that price.

As noted, they're really accurate meters. Worth keeping one around for emergencies.

( I also did a more extreme test of one of them here:   )

[paulie]

It's pretty quick - faster than a Fluke 27, for example - but very scratchy and rather anaemic.

I can live with scratchy (older Excel versions had solid tone) and anemic can be fixed with some holes in the case. It's not possible to live with slow response though. There's a meter costing almost 100x more gathering dust here due to delayed beep. 90% of my use is continuity so this is very important.

I got a few B.O. for $4 and change so would have to agree now this really is very close to "Worlds Cheapest". IMO definitely "Worlds Best" if the signal generator and beeper work out. Cheap, accurate, cheap, compact, cheap, and commonly available.

ps. Did I mention cheap?

[McBryce]

Several of the customers and friends I gave meters to ignored my warning and decided to measure amperage of their car battery by putting probes across or the like with expected result. In all cases it was the wires that went first. IMO those runs are more than adequate for 10a.

A car battery?? Shorted?? They can push >60A! That'll fry anything including your best Fluke, never mind some $3 dollar Chinameter.

McBryce.

[paulie]

No kidding. It's not certain that's what they actually did in every case. Maybe tried to measure mains voltage on resistance or current range. But it's the general idea. I've got a whole box of dead HF meters, probably with no more than blown fuse.  9v batteries were salvaged but not worth fixing considering the price.

I should have mentioned that to qualify for "Worlds Best" these Ebay units should have a fuse too. If not then first order of business solder in a thin wire across those pads.