Products > Test Equipment
BM869S not reading correct voltage
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LDDM:

--- Quote from: J-R on July 12, 2024, 06:52:25 pm ---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?

--- End quote ---

Yes, like you said, it is very well sealed, with o-rings at the jack, battery, and all around the shell as well. I would love to check it with a microscope, but I need to buy one.

I will order one and see if I can find something, but by looking at the board closely, I did not notice anything unusual. By the way, any recommendations for a cheap USB or HDMI microscope?

Yes, I have checked the fuses on both meters, and they are all okay.

I was using a Duracell Plus (6LR61) in the first meter and a Varta (6LP3146, long life Alkaline) in the second meter. Yesterday, I bought a cheap brand (PKCell 6LR61 long life "Ultra" alkaline :-//) to try and see if it makes any difference.

Unfortunately, no difference at all.
LDDM:

--- Quote from: BeBuLamar on July 12, 2024, 07:23:17 pm ---Can you send it to manufacturer for repair at reasonable cost?

--- End quote ---

I did not check what it would cost yet, i have to ask local post, DHL and Fedex.


--- Quote from: robert.rozee on July 13, 2024, 01:51:24 am ---
have you checked the meter leads using a known-good multimeter? this meter may be even the cheapest "dm830" giveaway from harbour freight.

from your results i'm rather suspicious that all your leads have been 'stretched'; when a multistranded cable is stretched it is possible for every strand to be broken, but each in a different location down the length of the cable. the result is that while the cable may appear to have end-to-end continuity at first, over time as oxidization occurs due to moisture ingress the cable becomes highly unreliable. it could well be that the sheathing Bryman uses happens to be particularly susceptible to moisture ingress in high humidity environments.

the risk of stretching cables is why meter leads should never be wrapped tightly around the instrument, or in any other way subjected to force along their length. good leads are made of multiple very fine strands to provide for flexibility, and those fine strands are more susceptible to breakage than heaver ones.


cheers,
rob   :-)

--- End quote ---

I only tested resistance of the lead with the multimeter itself (which seems good), they were my only multimeters seens i bought them, so i have to buy a new one / borrow to check. However, is tested with my PSU lead witch are good.
J-R:
For sure an odd situation, still feels like we're missing something...

But maybe Brymen got a bad batch of a component.  You could e-mail them with the serial numbers and see if they come back with any help.

Some other random thoughts:
- enter calibration mode and note the display in different switch positions, but don't actually calibrate it (https://www.jackenhack.com/calibrating-brymen-bm-series-multimeter/)
   (on my BM869s, I get 2.50000 for VFD and VAC, 0.00000 for VDC, 000.000 for mVDC, 250.000 for mVAC, 0000.0C for T1/T2, 000.00 for capacitance, 250.000 for resistance, 50.0000 for A/mA and 500.000 for uA.)
- connect maybe around 1VDC to the input and using another DMM, follow that 1V input as far as you can on the PCB to see where it goes
- also with the same 1VDC, bypass the obvious parts of the COM & V input protection and see if there is a difference
- power the DMM with a DC supply (carefully!!!) and note the power draw, or, are the 9V batteries still full after using them with the DMM for a bit?
LDDM:

--- Quote from: mqsaharan on July 13, 2024, 05:01:01 am ---
--- Quote from: LDDM on July 12, 2024, 07:16:11 am ---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.

--- End quote ---

If all else is all right, I mean, if there is no problem with the support circuitry of the processor(s), it could be (analog front end) processor die rot. As Dave once said and I quote "One of the failure modes seem to be related to some sort of processor die rot."
https://www.eevblog.com/forum/testgear/brymen-bm789-360289/msg5042728/#msg5042728

And in his next message (in the same thread,) he said that Brymen uses well known brand but he cannot disclose because of NDA.
I think it is Fortune Semiconductors. For some of their meters, they might be using custom chips but I doubt it will be the case with all their products.

I don't own any Brymen meters. I might have tried to trace the circuitry to figure out the chip they are using.


--- End quote ---

So, if the failure I'm seeing is related to this, there is little to zero chance that it could be fixed, right? Unless I can get a working processor and the matching firmware.

I would love to send one of them to Dave if he wants to have a look at it. I even have a family member going to Australia next week, so it would be cheap to get it there.

I will investigate and see if I can find the issue, but I have to buy a new meter first!
LDDM:

--- Quote from: J-R on July 13, 2024, 08:04:20 am ---For sure an odd situation, still feels like we're missing something...

But maybe Brymen got a bad batch of a component.  You could e-mail them with the serial numbers and see if they come back with any help.

Some other random thoughts:
- enter calibration mode and note the display in different switch positions, but don't actually calibrate it (https://www.jackenhack.com/calibrating-brymen-bm-series-multimeter/)
   (on my BM869s, I get 2.50000 for VFD and VAC, 0.00000 for VDC, 000.000 for mVDC, 250.000 for mVAC, 0000.0C for T1/T2, 000.00 for capacitance, 250.000 for resistance, 50.0000 for A/mA and 500.000 for uA.)
- connect maybe around 1VDC to the input and using another DMM, follow that 1V input as far as you can on the PCB to see where it goes
- also with the same 1VDC, bypass the obvious parts of the COM & V input protection and see if there is a difference
- power the DMM with a DC supply (carefully!!!) and note the power draw, or, are the 9V batteries still full after using them with the DMM for a bit?

--- End quote ---

Just checked the serial numbers, and they could be from the same batch: MFR.#: xxxxxx240 and xxxxxx185 (all "x" are the same).

Regarding the values in calibration mode, I also have the same on both meters (VFD: 2.50000, VAC: 2.50000, VDC: 0.00000, mVDC: 000.000, mVAC: 250.000, T1/T2: 000.0C, Diode/Cap: 000.00nF, Resistance: 250.000, A/mA: 50.0000, and uA: 500.000).

I powered the meter with my RD6006P at 9.1V, and it drew 0.0038A with a peak at 0.0051A, depending on the mode.

For the other tests, I will buy a multimeter locally (might be a Uni-T for now) and revert back.
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