This is why you don't buy cheap multimeters.

[retiredcaps]

Re: This is why you don't buy cheap multimeters.

What were you trying to measure? The explosion does look pretty spectacular.

Details at

http://www.eevblog.com/forum/index.php?topic=2585.0

A few times I tried to measure DC on the AC mains - again, no explosions. Perhaps I've been lucky?

See the very popular $4 or less Harbour Freight multimeter on Fluke's test and safety promotional video.

http://assets.fluke.com/video-MULTI/...afety_lab.html

The above multimeter is shown near the end of the video. Unfortunately, there is no timestamp that I can see on where it starts, but you get to see the flames in slow motion.

I think the Harbour Freight multimeter is set to 200 ohms when it is fed with 300+ DC volts.

[severach]

Re: This is why you don't buy cheap multimeters.

The same way everyone ruins their first meter:

"So this plug can supply 15 amps, eh? I can check that with this amp scale."

Then you learn that measuring amps is not like measuring volts.

[tom66]

Re: This is why you don't buy cheap multimeters.

What were you trying to measure? The explosion does look pretty spectacular.

I can't remember, might have been some high current or voltage. I was just shocked when smoke started pouring out the back of it. It might have been a manufacturing defect because I've still got one of those meters and it's survived many more abuses.

Did it look like this? I got this one free, but not working.

Nope, it was this one: http://www.rapidonline.com/Tools-Equ...st-leads-31052

[999999999]

Re: This is why you don't buy cheap multimeters.

Sometimes the problem is poor knob contacts, you might try popping it off and cleaning the areas.

[Agent24]

Re: This is why you don't buy cheap multimeters.

Well, since a couple weeks ago it started working erratically on resistance. More specifically, on the low ranges it reads in the hundreds of ohms even if there's a short, then it slowly counts down to the real value...

I noticed a similar problem (though not as bad) with my meter (it's one of the better-built 830B types)

Turned out to be dirty contacts on the rotary switch.

I cleaned the copper springs on the knob and the gold contacts on the PCB and haven't had the problem since.

[Th3_uN1Qu3]

Re: This is why you don't buy cheap multimeters.

Well, since then, i have dropped it (a few months ago) and it now displays entirely rubbish. So it's definitely not the range switch which is the problem on mine.

[Agent24]

Re: This is why you don't buy cheap multimeters.

Maybe the spring-contacts went out of alignment from the drop? They just sit there on a little plastic ledge (Though you probably already know and have checked that!)

[PeteS in CA]

Re: This is why you don't buy cheap multimeters.

This is normal for the 830B and part of it is due to the crummy probes it comes with. With good probes it should read 0.6 to 0.9 ohms when shorted.

This is a prime suspect - both the probes (either end) - and the banana sockets into which they plug. I'm spoiled rotten - HP 73As are the "worst" DMMs in my test area, plus some Fluke 187s and some top-end Agilent handhelds. When you're trying to set voltages in the 4000 volt range to +/- 1 volt, a +/-1%, 3-digit meter is not adequate. I'm not the paying for the meters I use, while you guys are. Still, cheap @#$% meters will cost you more in the long run - in $$ and time wasted - than a Fluke 10, 20, 70 or 80 series DMM (also, look into Extech, which seems less expensive, but still decent quality). This is in the US ... not sure what's commonly available in EuroLand and Asia.

[Th3_uN1Qu3]

Re: This is why you don't buy cheap multimeters.

In EU you can find Uni-T meters. Uni-T makes pretty good stuff. From bottom-of-the-barrel to Fluke level accuracy, they got everything covered. What you pay for is what you get. Uni-T is from China so no problems getting them in Asia either.

[retiredcaps]

Re: This is why you don't buy cheap multimeters.

This is a prime suspect - both the probes (either end) - and the banana sockets into which they plug.

Since my 99 cent 830 variant from ebay arrived DOA back in June 2010, these probes were NEVER used and have been put away. I took them out last week due to some of these threads and it literally fell apart in my hand.

Evidence.

And yes PeteS, I have much better quality name brand multimeters now.

[retiredcaps]

Re: This is why you don't buy cheap multimeters.

Uni-T makes pretty good stuff.

I'm thinking of getting a low end one (at the right price) just to see myself first hand what they are like. I have read most of the reviews here and at eevblog.

[mockingbird]

Re: This is why you don't buy cheap multimeters.

I have a DM210 and DM350, two real low-end meters... The DM210 works fine and I have had it now for a while... The DM350 I got recently. I turned it on and it was giving me very erratic readings. I opened it up, just to peek inside, and then I put it back together. I don't know what I did, but nothing comes up at all now. The LCD has some really weird connection, like some sort of plastic block with black things sandwiched in-between that somehow links it to the PCB... Does anyone know how that works?

Oh yea, the difference between them is that the 210 has only voltage and Ohm, and the 350 has a diode finction, so I have been using the 210 as a glorified battery tester.

[retiredcaps]

Re: This is why you don't buy cheap multimeters.

The LCD has some really weird connection, like some sort of plastic block with black things sandwiched in-between that somehow links it to the PCB... Does anyone know how that works?

Post some pictures please. I'm always curious to see the insides of any meter.

[mockingbird]

Re: This is why you don't buy cheap multimeters.


And here is the PCB (Full size 300+ KB version is attached to this post)L


Fuse is ok... Could it be the custom IC or you think it's a diode or transistor?

[retiredcaps]

Re: This is why you don't buy cheap multimeters.

The LCD has some really weird connection, like some sort of plastic block with black things sandwiched in-between that somehow links it to the PCB... Does anyone know how that works?

That black/pink thing is a zebra stripe.

http://www.repairfaq.org/REPAIR/F_au...#AUDIOFAQC_012

For those curious, I figured out these are Sperry brand multimeters through some searching. Sperry DM-210A and DM350A.

[retiredcaps]

Re: This is why you don't buy cheap multimeters.

Fuse is ok... Could it be the custom IC or you think it's a diode or transistor?

If you are talking about that black circular blob, that is a chip on board (COB). It is probably a ICL7106

http://www.hobby-hour.com/electronics/icl7106.php

[mockingbird]

Re: This is why you don't buy cheap multimeters.

Thanks for the model... Yea, I knew it was the IC, I was asking if he thought the IC was the culprit or maybe a diode or resistor was shot. I've read about transplanting these ICs, but like Unique said, for a $5 DMM... I dunno.

[momaka]

Re: This is why you don't buy cheap multimeters.

Since my 99 cent 830 variant from ebay arrived DOA back in June 2010, these probes were NEVER used and have been put away. I took them out last week due to some of these threads and it literally fell apart in my hand.

Yep, cheap probes are cheap.
I was measuring some current last week with my 830D. After measuring about 1.7A for over 2 minutes, the wires on my probes were actually warm to the touch!
... and to think the meter can measure up to 10A. I bet the probes will melt at 5A.

[Th3_uN1Qu3]

Re: This is why you don't buy cheap multimeters.

I bet the probes will melt at 5A.

4A actually. Melted a few myself.

[momaka]

Re: This is why you don't buy cheap multimeters.


No wonder they don't put fuses for the 10A current setting - it's just not needed when the probes are acting as a fuse .