BM869S not reading correct voltage

[LDDM]

Hi Everyone,

First post here. Some time ago, I bought a BM869s after watching some videos of EEVblog on YouTube. The first one I received had a leaking battery, so I was sent a second one and was never given a return label for the first one.

Long story short, I repaired the first one and had 2 brand new BM869s. Both of them were working perfectly for 1.5 years of really light use (for hobby project). However, the last time I used them, for some reason, both gave me incorrect voltages AC and DC.

At first, it was with AC voltages from mains power (230V). I measured between Live and Neutral and only got around 156V (now it is 0V). I did the same with another multimeter (Major Tech brand) and I had the expected voltage (230V to 240V). Then, I tested with my power supply (RD6006P) a DC voltage and had the same issue: I got lower voltage than expected (please see pictures below).

Has anyone had this issue? Can it be resolved, or is the multimeter fried (both have a similar issue)?


Please also see video here: https://youtube.com/shorts/29_wXrWJ6-4?feature=share

[Fungus]

It seems impossible that both would fail simultaneously. These are very robust meters.

There must be some information missing.

[LDDM]

Maybe I did something wrong by accident, but these are not the first meters I've used, and I've never managed to break a meter before. Additionally, I did not do anything unusual with them, only measured battery voltages, voltage in small circuits (ESP32, Arduino, and similar), and very few times mains voltage.

What could cause this sort of issue?

(Note: The first meter with a leaky battery also had an issue with the amp jack sensor, which I fixed.)

[LDDM]

I just found someone with a similar issue, it seems:

https://www.eevblog.com/forum/testgear/brymen-bm869s-no-longer-reading-ac-voltage/msg5529979/#msg5529979

Update: Also find this (I'm having this issue as well)

[joeqsmith]

I bought my first one in 2016.  Even after all of my abuse, both meters continue to work fine.  For two to fail, there's more to the story.

Switch point hunting is a common problem.  Agree, it should never happen but it's not something that has ever caused me a problem outside of the reviews.   The BM789 should be solid in this regard. 

[Martin72]

A few questions for the OP:
-Batteries in the devices are OK ?
-Test leads OK?
-Have you tried a different voltage source, e.g. a battery?
-Tested other measuring ranges, current, resistance, capacitance, frequency?
-What are the environmental conditions where the meters are usually located, i.e. average temperature and especially humidity?
It is very unlikely that both have broken, unless both have suffered the same fate.

[TheDefpom]

Maybe try a different set of test leads, if you are using the same pair of leads that could be the problem instead.

[radiolistener]

I just found someone with a similar issue, it seems:

I know Brymen brand by their faulty gold-plated probes.

The one pair that I got with my new Brymen BM867S is going to 5-10 Ω resistance just after 2-4 years of very rare and light usage (just as a home dmm for diy projects). I contacted with Brymen about it and they said the following:

For reliability, our test lead design uses mechanical grab to harness wire for connection. Its design does not use soldering. Thus its loop resistance is slightly higher naturally. You may use Relative feature to offset it.

The tips of your test lead set should be already with some oxidized stuff. You may try using a cloth or tissue with a little of baking soda powder to dry clean their tips by rubbing. Our experience told us it could solve their unstable resistance problem.

In reality there is some issue with contacts inside probes banana plugs, if you push and pull the wire back and forth it can solve issue for some time, but it again going worse and worse with time. So there is no way to fix it with no probe disassemble. And if you disassemble it you can just put it into garbage bin because it has not repairable design.

So, first try to replace original Brymen gold-plated probes with some new one from another brand, even cheap Chinese 2 USD probes should work better.

[Antonio90]

As @radiolistener said, try different probes or a cable with banana plugs. I have a set of brymen leads with intermittent connection problems. Drove me crazy for a while too.

[LDDM]

Thank you for your replies. If I did something wrong, I genuinely do not know what, but I would happily take the "blame" and learn from it!

How can something like this happen? What would it take to break a meter like this?

(Note: No blown fuses, no burned components in the meter.)

Moreover, I replaced both 9V batteries this morning and tested the test leads / used banana test leads from my PSU with no luck.

So I did a few tests to see, please see the table below:


 

[J-R]

The selector switch on the BM869s has multiple pieces with wipers in specific locations.  Any chance you disassembled that and didn't reassemble it 100% correctly?

[Fungus]

How can something like this happen? What would it take to break a meter like this?

Without disassembling it? A lot.

Two of them breaking simultaneously is very suspicious.

[coromonadalix]

yep strange issue ... 2 of them ? 

i would have said  high voltages spikes, blown fuses,  battery  ... the usuals suspects ??

if probes are ok  not loose  ... dismantling associated problems ... sure its hardware related ...  movs  tvs ... bad dial contacts or broken ones   

probing inside them   ....    ask brymen for a schematic under non disclosure if they would help in some ways

you do need to read the internal dividers in manual mode and keep the same impedance for many ranges ... ? 
you have many schematics with the meter chipset who could help you follow voltages paths ...

[Fungus]

How were they stored? Could they have been exposed to weird vapors or liquids?

Could anybody have "borrowed" them without you knowing?

[LDDM]

Yes, so I disassembled the first meter to replace the 9V battery connector after the provided battery leaked and seeing the seller did not want to get it back (it was replaced under warranty). Afterwards, the meter turned back on but was stuck with "InErr" (jack beep). I managed to find the issue: the two sides of the amp jack were connected together due to a soldering issue, causing the meter to think the lead was in the amp jack. After that repair, the meter went back in the box, so I never really used it (except one time where I had to measure the temperature in my fridge) so maybe it had other problems that i did not see at the time.

Yesterday, I disassembled the rotary switch of this meter for the first time (to check if it could be the cause of my problem). I marked with a Sharpie the position of the switch before taking it apart and took the following pictures (please ignore the position of the lead, was testing the jack beep feature).

For the second meter, I never disassembled the switch, i only check if i could have blown a fuse (none were blown).

The strange thing is that the last time I used my main meter (the second one) several months ago, it was working normally and has been sitting unused on my desk until now. o my knowledge, no one has used it besides me.

I live in a tropical climate with temperatures around 25-35°C and humidity over 80%.

I will try to clean the board of the first one with some electronic cleaner and see if it makes any difference.

Update: Forgot one picture

[joeqsmith]

You work on electronics without proper ESD protection? 

I see three photos of one side of the switch, none of the other. 

[coromonadalix]

?  is the dial has being flipped by mistake or a contact has flown into space

you have 3 pairs of pcb traces and i see only 2 contacts = 2 pairs    

you seem to miss the one near the center hole m or more than 3  since you have some level shifting in the pcb traces


search for teardown videos

this site has photos who does show 2 contacts

https://lygte-info.dk/review/DMMBrymen%20BM869s%20UK.html

[Fungus]

You're definitely missing some switch contacts here...

(I think there should be four of the gold spring things on the dial)

[Martin72]

I live in a tropical climate with temperatures around 25-35°C and humidity over 80%.

Phew, that's right on the edge.
For such regions, we install dedicated "tropicalized" measuring devices in our system, for example.

[coromonadalix]

yeah    but  see my link on my post    we see only 2 contacts

https://lygte-info.dk/review/DMMBrymen%20BM869s%20UK.html

a simple dial miss-alignment in functions

[LDDM]

Sorry  i forgot one picture (please see update to my previous post, Meter_16)

[Fungus]

yeah    but  see my link on my post    we see only 2 contacts

https://lygte-info.dk/review/DMMBrymen%20BM869s%20UK.html

Here, too...

https://www.eevblog.com/forum/testgear/brymen-bm-867-teardown-pictures/msg156229/#msg156229

But that makes no sense to me.      

[LDDM]

I just found this post from 2022 of someone having (I think) the same issue.

https://www.eevblog.com/forum/testgear/brymen-bm869s-suddenly-weird-behaviour/

Similar thing here. It seems to be more common than I thought...

https://www.eevblog.com/forum/testgear/brymen-bm869s-stopped-measuring-ac-volts/25/

Port from 2018 with similar problems:

https://www.eevblog.com/forum/repair/brymen-bm869s-ol-problem-with-ac-measument/msg1918175/#msg1918175

[joeqsmith]

Sadly as you have seen, seldom people who post about their problems ever provide a conclusion. 

I live near fresh water and it's not a problem like other parts of the USA.  I've never had to consider conformal coating.  Do you have to store your electronics in special containers or is not a problem where you live?  Is the humidity always high enough that ESD isn't a concern?   

[J-R]

The BM869s is actually pretty well sealed.  There are gaskets/o-rings around the battery cover and the banana jacks, even the screw heads.  So I don't think humidity would impact it.

But you could still fully inspect the PCB under a microscope looking for any solder issues or corrosion, clean selector switch and jack contacts.

A side note is that each jack's BeepJack feature does not function if their respective fuse is blown, so double-check those.

What 9V batteries are you using?