EEVblog 1667 - Reverse Engineering the Brymen BM2257 Multimeter LowZ Mode

Reverse Engineering the Brymen BM2257 Multimeter front end to understand what changes have been made from the BM235 in the Low Z mode. DaveCAD time. Also some testing of the LowZ mode and how it works.

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[trader]

Love these teardown RE videos. Always learn something new.

[humidbeing]

lowz is super useful for automotive repair, where ghost voltages are super common red herrings that cause tons of wasted time and unnecessary part swapping.

[bacphan]

In School: An ideal voltmeter have infinity resistance. Engineer: LOL no we gonna short circuit the shit out of it

[hadibq]

great thing that Orange backlight, I thought I'm the only one loving that. I love eevblog meters 👍👍 I think I'm gonna get that one too only for the backlight haha

[ferrumignis]

I learnt something interesting about PTCs recently; at high temperatures the capacitance between the semiconductor grain boundaries increases, so the PTC impedance becomes strongly frequency dependant. The capacitance can be high enough for relatively low frequencies to have a significant effect e.g. in the example chart shown in a TDK document it shows the impedance at 1kHz is nearly two orders of magnitude lower than at DC. Not a problem a line frequencies, but potentially bad news if a high frequency voltage is sufficient to start the PTCs working.

[ElliottVeares]

Imagine using the Low Z mode to measure 3 phase voltage at 400v AC. That's nearly 70W of dissipated power by my calculations at 2.3K ohms.

[qzorn]

Most excellent!🎉 I have seen people chasing their tail testing voltage in a bundle of wires when the false signal was induced from a different live circuit.

[monstergamingff]

This is what i am looking for, thank you for video 😊

[lucafurna]

Great reverse engineering video about a nice cute small DMM!

[khangaudio]

❤❤❤ everyday i repair radio cassette. when i know your videos. i learned some things. thank you very much

[Petertronic]

It's back! This video disappeared when I was about to watch it, haha

[andymouse]

Confidence is low...I repeat confidence is low.

[richardbrobeck]

Great meter !! great price on the BM2257 the price is great too !

[BlownF]

I know it not in the electronics vein but I would love to see an EEVblog AC/DC clamp meter for those of us that do residential/commercial electrical trouble shooting.

[EsotericArctos]

I like the Low-Z mode. That is a really great idea. I'd also like an ultra high Z mode, something similar to what Vacuum Tube / Valve Volt/Ohm meters can provide. I sometimes do measurements that require the meter to be virtually invisible to the circuit, with impedance high enough to remain invisible to the circuit under test. Actually, a High Z analogue meter would be a welcome addition. These seem to be hard to find new

[threeMetreJim]

Strange how Brymen are so adverse to releasing a schematic. Not like there is a great deal on the boards nowadays with everything being done in firmware; without which a copy would be non-functional (You'd have to have the dev kit for an SDIC IC and a coder). Just makes minor repairs more tedious.

[sdp]

I picked up a BM2257, it's a bobby dazzler.

[rialtho_the_magnificent]

I always wanted a DMM like the one above and I finally got one. For some reason it's in a RED cover and it came from Poland (I live in the Netherlands). Strange that the supplied batteries were carbon zinc and not alkaline. Now I have to 'play' with it to see what the additional options are compared to my 20+ years old DMM, which is running on it's last legs.

[urugulu]

if would wanna know if a cell has high esr (and i do not have a esr meter; and when we arent talking 18650 or similar high power cells) i would short out the battery with a meter in amps mode -- if i get a reasonably large current the cell likely isnt too bad (which i know might be bad advice)

[karim]

Hi Dave, if you manage to convince Brymen to spec the DMM to your likings, why couldn't you add a "Inductance" menasuring mode that uses your "inverse 2pi trick" in capacitance mode? It would have been so convenient.