A830L Teardown/Review. A cheap multimeter with a mystery function. - Page 1
Forum section: electronics / testgear

author: lmester
author_rank: Regular Contributor
timestamp: June 11, 2018, 09:13:25 am
content: First, the mystery function. This meter has a setting marked with mA (capacitor symbol) 1.5V on the rotary switch selections. See the pictures. This is not a capacitance measurement function. Any value of cap connected to the leads shows a value of 0. The probes have no voltage or waveform on them when this range is selected.I used A bench power supply to feed A current limited voltage into the probes. This showed that this setting was actually measuring current in mA's with a voltage drop across the meter probes of 1.5V. I've got no idea what use that this might have. A mA current scale with a 1.5V burden voltage?? Does anyone have any ideas what this selection does? This function may not be working properly on this meter. That's possible since this meter is a really cheap piece of crap.Review/Teardown:Not much of a teardown. Only a few Phillips screws :-)I shouldn't have purchased this multimeter. I have no need for a cheap meter. I just couldn't resist. It cost only $6.00 with free shipping.How can you sell a meter with all of these functions/features for $6.00? My Fluke 87 cost over $300! My bench multimeters were purchased used and cost nearly as much.Why is this meter so inexpensive? I've thought of several possibilities...The economy of using an ASIC:You can see from the pictures that the PCB has a COB with only a few discrete components. Mostly SMD resistors.The build quality is very poor:When I pulled the package from my mailbox, I could hear something rattling around inside. There was an extra screw loose inside the meter case.The positive test probe tip came apart while I was pulling the probes out of the box. This exposed the probe conductor. I'd guess It's about #22 wire. Check the picture. Bad things could happen when using these probes with the 10A current range. "My probes are melting and my fingers are sizzling :-)"Banana jack conductors are rusty.Piezo beeper is just dangling by it's leads.Overload protection & safety:This meter has a CE certification.I've never done any research on the CE mark. What does this actually mean?For this meter, I'd say that "CE" might mean "Could Explode" during an overloaded!The manual lists a 500mA fuse for the low current range. The fuse holder pads are on the PCB but, no fuse is installed.The manual also says that it can handle A 250V RMS overload on the voltage and resistance ranges. I might test this. First, set the meter to a resistance range. Next, put on a pair of gloves. Then, place the meter far away from my body. Finally, Insert the probes into a 240V receptacle. Does it go Boom! or, just show an overload?The 10A current shunt also has no fuse.They did trim the shunt resistance. Several crimps in the shunt wire to increase it's resistance are visible. Amazing for a $6.00 meter! Someone actually did some calibration of this meter!There is some good news for this cheap meter.I did some tests on the DC Volt ranges.It's manual claims .8% accuracy on DCV.It met this spec out of the box. With A little tweaking of the only calibration pot on the PCB it was much better. It was even consistent when switching between all DCV ranges.I've not yet tested the Resistance, ACV or current functions.

author: sleemanj
author_rank: Super Contributor
timestamp: June 11, 2018, 09:53:00 am
content: "Mystery function" is a "battery tester", it applies a load of 42 ohms across the COM and V jack, and displays in milliamps the short circuit current of a battery under test. A good 1.5v battery thus (by Ohm's law) should produce around 35 mA.

author: David Hess
author_rank: Super Contributor
timestamp: June 11, 2018, 11:22:37 am
content: I agree with sleemanj; it is a 1.5 volt battery check function. The capacitor symbol is a poorly drawn battery cell symbol.

author: 001
author_rank: Super Contributor
timestamp: June 11, 2018, 08:47:02 pm
content: Wery funny storyRead manual first!