Author Topic: BM789 continuity behaviour  (Read 7216 times)

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Offline giosifTopic starter

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BM789 continuity behaviour
« on: September 03, 2023, 11:58:53 am »
Has anyone else noticed this rather annoying behaviour with the BM789 in continuity mode where, when connecting the probes to a part of a circuit where there is no continuity (or low resistance), it gives a short beep, but then stops.
If you then move one of the probes away from the part of the circuit to which it was connected, wait for a second or two, the connect back the probe, you get the short beep again.
To be clear, I'm not talking about parts of circuit which have capacitors connected.

This is annoying because, when trying to trace connections on a board, you get distracted by all these false positives and you end up having to keep the probes in a given location for longer, to make sure the meter beeps because of actual continuity.
In other words, the meter's fast response in continuity mode is being defeated by these (brief, but often) false positives.

Also, it is interesting that a BM257s or a 121GW do not exhibit this behaviour on the same board, same connection points, and same probes (i.e. these other meters don't beep at all in those same locations).

Could it be that the BM789 in continuity mode is too sensitive to the stray capacitance in the circuit and/or meter probes?
 
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Offline giosifTopic starter

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Re: BM789 continuity behaviour
« Reply #1 on: September 03, 2023, 12:10:20 pm »
Just adding another observation I've just made (again, with the BM789 in continuity mode): if I hold one of the probes in my hand (touching the metal part) and I touch the other probe to a piece of metal somewhere in my lab (I've used the boom stand of my microscope for this test), I also get the short beep.
 
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Offline LuisBe

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Re: BM789 continuity behaviour
« Reply #2 on: September 03, 2023, 12:46:35 pm »
Sorry for my level of English, everything I write is done with a translator. I have just checked that my BM789 does the same as yours, both in the circuit and against the chassis of a remote and unconnected equipment. I have measured the resistance between the short beep points in the circuit and there is 1.35 Kohms.
 

Offline BILLPOD

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Re: BM789 continuity behaviour
« Reply #3 on: September 03, 2023, 01:31:56 pm »
I have a similar experience with my 121GW in 'reverse' continuity mode.
Actually it's called cable testing mode, but it's supposed to beep when continuity is broken.   I get these short beeps when I test a suspected open in a DMM test lead :wtf:
 

Offline siealex

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Re: BM789 continuity behaviour
« Reply #4 on: September 03, 2023, 02:46:46 pm »
Is the continuity mode combined with the diode test mode? A short beep in this mode means a forward voltage drop between 0.1 V and 2.0 V for a normally functioning diode.
 

Offline giosifTopic starter

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Re: BM789 continuity behaviour
« Reply #5 on: September 03, 2023, 04:08:41 pm »
Sorry for my level of English, everything I write is done with a translator. I have just checked that my BM789 does the same as yours, both in the circuit and against the chassis of a remote and unconnected equipment. I have measured the resistance between the short beep points in the circuit and there is 1.35 Kohms.
Thanks for confirming!


I have a similar experience with my 121GW in 'reverse' continuity mode.
Actually it's called cable testing mode, but it's supposed to beep when continuity is broken.   I get these short beeps when I test a suspected open in a DMM test lead :wtf:
Hmmm... I don't think this is the same problem, even assuming the DMM test leads you are testing are good (although, it sounds to me the issue you are seeing is caused by those leads).


Is the continuity mode combined with the diode test mode? A short beep in this mode means a forward voltage drop between 0.1 V and 2.0 V for a normally functioning diode.
No, this is continuity/low resistance mode only.
Diode test mode is a separate function with this meter.
 
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Offline LuisBe

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Re: BM789 continuity behaviour
« Reply #6 on: September 03, 2023, 04:49:53 pm »
I just made a home video and uploaded it to youtube in hidden. I have no idea how to upload videos, nor how to edit videos so I hope you can forgive me if I did something wrong.
I compare the same actions with a BM235 and with a BM789 on a chinese arduino board.

I have deleted the video in this post because I had an error in my installation. There are two videos further down the thread where it is explained.
« Last Edit: September 06, 2023, 06:02:46 pm by LuisBe »
 
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Offline giosifTopic starter

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Re: BM789 continuity behaviour
« Reply #7 on: September 03, 2023, 05:27:12 pm »
I just made a home video and uploaded it to youtube in hidden. I have no idea how to upload videos, nor how to edit videos so I hope you can forgive me if I did something wrong.
I compare the same actions with a BM235 and with a BM789 on a chinese arduino board.

Thanks for the video!
That's exactly the behaviour I am talking about.
 
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Offline LuisBe

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Re: BM789 continuity behaviour
« Reply #8 on: September 03, 2023, 05:38:19 pm »
Thank you for informing us of the anomaly.
 

Offline mwb1100

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Re: BM789 continuity behaviour
« Reply #9 on: September 03, 2023, 05:52:02 pm »
FWIW (probably not much), I cannot reproduce this behavior with a BM786 that I bought from welectron 1 year ago.
 
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Offline giosifTopic starter

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Re: BM789 continuity behaviour
« Reply #10 on: September 03, 2023, 06:55:01 pm »
FWIW (probably not much), I cannot reproduce this behavior with a BM786 that I bought from welectron 1 year ago.
Thanks for checking!
That's good to know, since the BM786 is part of the same series as the BM789.

I have contacted Brymen about this issue; let's see what they say.
In the meantime, anyone else owning a BM789, could you please test and report here, so we understand how widespread this problem is?
 
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Offline Electro Fan

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Re: BM789 continuity behaviour
« Reply #11 on: September 03, 2023, 08:24:23 pm »
Just adding another observation I've just made (again, with the BM789 in continuity mode): if I hold one of the probes in my hand (touching the metal part) and I touch the other probe to a piece of metal somewhere in my lab (I've used the boom stand of my microscope for this test), I also get the short beep.

I haven't read this whole thread but my 789 doesn't do that.
 

Offline Caliaxy

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Re: BM789 continuity behaviour
« Reply #12 on: September 03, 2023, 08:41:16 pm »
My 789 does something similar, too: random very short beeps when touching metal parts of various equipment with only one probe (the other probe in the air). Looks like some static charge pick-up - touching repeatedly the same metal part does not result in multiple beeps; you have to wait a bit or touch something else before being rewarded with a new beep. Not sure what to make of it...

Haven't noticed it (and it never bothered me) until reading this post. Thank you, Mr. giosif :)

Bought from Welectron in 2001.
 

Offline giosifTopic starter

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Re: BM789 continuity behaviour
« Reply #13 on: September 03, 2023, 09:10:21 pm »
[...]
Haven't noticed it (and it never bothered me) until reading this post.
[...]

To be clear, the behaviour on its own doesn't bother me; what does, though, is its impact on being able to use the meter's continuity function to trace connections in a circuit.
In other words, because of all these beeps I get when placing the probes on points which are not actually directly connected, I have to keep the probes in a given location long enough until the beep stops, before I can determine there is no connectivity and can move on to the next location.
And this is no better than having a multimeter with a slow response time in continuity mode.

Have you used your BM789 for this purpose?
 

Offline Caliaxy

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Re: BM789 continuity behaviour
« Reply #14 on: September 03, 2023, 09:43:28 pm »
And this is no better than having a multimeter with a slow response time in continuity mode.
True.

Have you used your BM789 for this purpose?
Not that much, it's not my primary meter. I actually tend to avoid it, for reasons other than this one (now I have one more reason...)
 

Offline Electro Fan

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Re: BM789 continuity behaviour
« Reply #15 on: September 03, 2023, 10:17:09 pm »
My 789 does something similar, too: random very short beeps when touching metal parts of various equipment with only one probe (the other probe in the air). Looks like some static charge pick-up - touching repeatedly the same metal part does not result in multiple beeps; you have to wait a bit or touch something else before being rewarded with a new beep. Not sure what to make of it...

Haven't noticed it (and it never bothered me) until reading this post. Thank you, Mr. giosif :)

Bought from Welectron in 2001.

OK, this thread has me testing more.  Mine does the same as Caliaxy describes:

random very short beeps when touching metal parts of various equipment with only one probe (the other probe in the air). Looks like some static charge pick-up - touching repeatedly the same metal part does not result in multiple beeps; you have to wait a bit or touch something else before being rewarded with a new beep.

I can reproduce this ^ .  Not sure what the interval is between no random beep and a random beep but sometimes it seems less than a minute.  I have tried various combinations (meter off/on, replugging leads, etc) to find the pattern and interval but so far it just seems like a random beep and a random discharge.  In one instance I found that just plugging in the red lead caused a beep.

In typing this for about 2 minutes I had the meter off.  When I turned it on and touched just the black lead to an Arduino component I got a beep; within a couple seconds I pulled the black lead off and touched it with my fingers and got another beep.  2 minutes later after more typing I just touched the black lead with my finger and got a beep.  Half a minute more typing and no beep from touching either lead.  Another half a minute of typing and a beep touching the black lead with a finger.  Another half minute of typing and no beep from touching either lead with a finger.   Another 30 seconds and no beep from a finger touch, but a beep from just touching the black lead to an Arduino circuit.  Red lead doesn't seem to be beep happy.

In exploring this rabbit hole I tested the leads for resistance with a 4 wire meter and didn't find anything surprising.  However, in an effort compare the leads to other leads I found that while most pairs show the same resistance on the black and red leads, one of my Fluke 175 pairs shows that one lead has about twice the resistance of the other.  If it isn't one rabbit hole it's another.

(After some more typing the black lead touched to an Arduino component gives a beep, followed by silence for about a minute, followed by another beep when touched to the Arduino circuit.  Then silence from any type of touch for about a minute.)

Edit:  After owning the 789 for  couple years or so and using it along side various other meters, I'd say that for anything other than continuity I think it is an accurate and robust meter - but it seems that in continuity mode it's a tad overly sensitive and and sometimes goes into "listen to me and look at me" mode.

- After sitting here for several minutes and getting no beep I turned it off and on.  Then touched an Arduino component with the red lead and got no beep, but within a couple seconds touched the black lead to the same component and got a beep.
« Last Edit: September 03, 2023, 10:28:13 pm by Electro Fan »
 

Offline Electro Fan

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Re: BM789 continuity behaviour
« Reply #16 on: September 03, 2023, 10:44:36 pm »
As per the attached images, these behaviors seem pretty consistent.  Maybe this can help someone better diagnose what's happening.
« Last Edit: September 03, 2023, 11:16:36 pm by Electro Fan »
 

Offline Electro Fan

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Re: BM789 continuity behaviour
« Reply #17 on: September 03, 2023, 11:51:15 pm »
Maybe grasping further at straws but when checking continuity with the Fluke 179 you can get a beep between the VOUT and the INPUT to repeat after about 10 seconds (or sometimes less).  With the Brymen 789 you can get a beep to repeat in about 3-4 seconds. 

Edit:  Or maybe not; my theory was that the Brymen is more sensitive to something but I can't confirm it - test results are too random.
« Last Edit: September 04, 2023, 12:01:47 am by Electro Fan »
 

Offline sonpul

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Re: BM789 continuity behaviour
« Reply #18 on: September 04, 2023, 07:33:17 am »
It seems to us that everything is allowed to us with a multimeter and we can demand everything. Despite the length of the wires and the huge interference when touching anything.
I can also call a short beep to something massive or a component on a PCB. I call a lot and often during the repair of devices, but this behavior has never interfered strongly. I perceive it as the behavior of a living organism or a feature of the character of a work partner.
 

Offline giosifTopic starter

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Re: BM789 continuity behaviour
« Reply #19 on: September 05, 2023, 05:58:35 pm »
It seems to us that everything is allowed to us with a multimeter and we can demand everything. Despite the length of the wires and the huge interference when touching anything.
I can also call a short beep to something massive or a component on a PCB. I call a lot and often during the repair of devices, but this behavior has never interfered strongly. I perceive it as the behavior of a living organism or a feature of the character of a work partner.

Do you own a BM789?
If yes, how often have you used it in continuity mode to trace circuits?
 

Offline sonpul

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Re: BM789 continuity behaviour
« Reply #20 on: September 05, 2023, 07:40:31 pm »
Do you own a BM789?

I use two BM789 in my work.

Quote
If yes, how often have you used it in continuity mode to trace circuits?

Often and a lot.
 

Offline giosifTopic starter

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Re: BM789 continuity behaviour
« Reply #21 on: September 05, 2023, 08:39:39 pm »
Do you own a BM789?

I use two BM789 in my work.

Quote
If yes, how often have you used it in continuity mode to trace circuits?

Often and a lot.

And, from your perspective, don't the spurious beeps significantly slow down your tracing process (i.e. making the experience similar to using a slow continuity response meter)?
Or it does, and you just learned to accept it?
 

Offline joeqsmith

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Re: BM789 continuity behaviour
« Reply #22 on: September 06, 2023, 01:39:06 am »
I tried to reproduce with my 789, firmware 78911 but no luck.   I tried with a single lead to various equipment, a large plate and sheet of foil.  Then tried both leads with foil, plate and other metal equipment.  I never had it trigger.   Foil sheets and plate were about 2' sq and floating.   Equipment I was touching off on is all grounded to earth.   Meter sitting on grounded ESD mat.   

Offline Electro Fan

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Re: BM789 continuity behaviour
« Reply #23 on: September 06, 2023, 03:39:34 am »
78905 produces random continuity beeps.
 
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Offline NoisyBoy

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Re: BM789 continuity behaviour
« Reply #24 on: September 06, 2023, 03:57:08 am »
No issue with 786.

I wonder if it is firmware version related. 

Not that it matters since Bremen will not provide end user firmware upgrade. But at least it may help for those who are shopping for a used 789 if it is firmware related.
 
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