Extech EX430 teardown

[Lightages]

I need to say that the problems are specifically with the EX series. The EX series are made by CEM. The MM series are made by Brymen and the quality control is completely different.

[retiredcaps]

Those four resistors must be some kind of input protection. Their value is too high (4 * 110k) to be the shunt resistors. Moreover mA and uA ranges still work.

Last question before I go to sleep.

Does the buzzer beep when you make an incorrect setting in the multimeter with respect to the A and uA/mA as per manual?

That is, if you have your black probe in COM and your red in uA/mA and the rotary switch set to DCV, does the EX430 beep and show the wrong connection indicator?

[retiredcaps]

Yeah, these pictures really show how much Extech cares about quality control.

CEM Instruments makes it for Extech, but since Extech's name is on the product, they should care more about what their partner produces.  Either Extech should get CEM to have a better process or dump them and get a different partner.

When an Extech representative was here, he would be participating and generally putting out fires like this, but I don't know if he could actually influence who Flir/Extech chose as a manufacturing partner?

[bazsa56]

Regardless of who manufactures what, the bottom line is you can't trust the Extech EX series, or anything Extech made by CEM. I don't really want to check who is the manufacturer of a particular Extech meter nor should I have to, I'd rather just get something from another manufacturer.

And yeah, I checked back in the forum and saw that Extech normally replaces these defective units, so at the very least the're customer service seems good, but that doesn't change the core issue.

[Grapsus]

Those four resistors must be some kind of input protection. Their value is too high (4 * 110k) to be the shunt resistors. Moreover mA and uA ranges still work.

Last question before I go to sleep.

Does the buzzer beep when you make an incorrect setting in the multimeter with respect to the A and uA/mA as per manual?

That is, if you have your black probe in COM and your red in uA/mA and the rotary switch set to DCV, does the EX430 beep and show the wrong connection indicator?

You're right, in Volts mode, an alarm turns on if I plug a lead into the 20A socket, but no warning with the mA socket.

[Grapsus]

I've populated the missing resistor and now the warning signal works with the mA/uA socket.

[retiredcaps]

I've populated the missing resistor and now the warning signal works with the mA/uA socket.

That is what I suspected and why I asked you test the warning buzzer.  I noticed that the EX430 had split input jacks and after looking at the Fluke 87 schematics for their input warning, I suspected that the resistors were for input jack warning.

So that is at least two multimeters now where I have helped people discover the functionality of the missing smd component.

[retiredcaps]

@Grapsus, Did you buy your EX430 brand new or used?

[Grapsus]

I bought it new from Conrad. It's still listed here :

http://www.conrad.fr/ce/fr/product/121640/Multimetre-numerique-Extech-EX430-CAT-II-1000-V-CAT-III-600-V-Affichage-nombre-de-points4000

I had a coupon so I paid 70 euros instead of 100.

[Hydrawerk]

I do not like the position of fuses. It is bad as my own multimeters. UT70A is the worst at this.

[Rasz]

I do not like the position of fuses. It is bad as my own multimeters. UT70A is the worst at this.

UT70A is <30 euro, and this comparison makes extech look even more ridiculous
at this price point I dont care if my uni/t dies.

[Grapsus]

I do not like the position of fuses. It is bad as my own multimeters. UT70A is the worst at this.

Yep, when the two boards are sandwiched together, the big current shunt and the fuses are just a few millimeters away from low-voltage circuitry underneath. Correct me if I'm wrong, but 6 kV can easily arc over a few millimeters of air...

[Hydrawerk]

The fuse should be easy to replace like this. Unfortunately, most cheap multimeters do not have this feature.
EDIT: I do not own this multimeter.

[RoboTechEd]

The fuse should be easy to replace like this. Unfortunately, most cheap multimeters do not have this feature.

I am impressed with that. Why dont more DMMs feature that? It doesn't seem like a technical marvel or anything. And with an Ex430 MSRP at >$100USD, it is something that should be standard for sure. Especially seeing where else they ignored cost

[Lightages]

Easily accessible fuses are not necessarily easy to implement. If you are designing a meter for safety then the fuses and any other internal circuit need to be sufficiently sealed away. If you make the fuses easily accessible it might make any internal explosion path a very shot one to the hand. It adds complication and cost to the design. Replacing fuses should not be a regular thing you need to do. If it is something you are doing regularly then you need to learn how to be less careless around electricity.

If a meter is rated for any kind of water proofing, then the design problems go up another magnitude.