FIXED ! - Brymen BM869S rejecting fresh 9V batteries.

[rob77]

Hi Guys !

did anyone experience a problem with fresh 9V batteries in a brymen BM869S ? i just changed a battery - used a same make of a 9v battery and when turned on the meter was beeping and displaying InERR on the display. that should be the case when the battery is drained and the battery goes down below 5V under 20mA load. but my brymen violently beeps with a fresh battery.
i tried a expensive varta long life 9V battery - and it does the same. tested the batteries under 20mA load and they're all above 8,5V under load.
with the drained battery the meter works (just showing the battery low sign). so i tried to discharge one of the batteries a bit and once the battery is ~8V the meter works just fine, accepts the battery and starts up normally. the readings are spot on - tested DC volts and Ohms.

if someone knows what the heck is going on please let me know.

[retiredcaps]

Just curious, does this problem happen if you use a DC variable power supply set to 9V?  If you are doing this test, what is the current draw?

[rob77]

Just curious, does this problem happen if you use a DC variable power supply set to 9V?  If you are doing this test, what is the current draw?

actually a good idea  tested it and it's drawing ~30mA at 9V and the meter starts up, as the voltage is lowered the current draw decreases as well - down to approx 18mA at 6V (all tested without backlight - just the meter itself).
don't know what such a meter should draw.. but 30mA looks a bit high to me.

[wraper]

Have you tried switching it on with leads removed?

[retiredcaps]

don't know what such a meter should draw.. but 30mA looks a bit high to me.

Manual says 6.5mA typical.  Time to take it apart and post some clear focused pictures?

[wraper]

Just curious, does this problem happen if you use a DC variable power supply set to 9V?  If you are doing this test, what is the current draw?

actually a good idea  tested it and it's drawing ~30mA at 9V and the meter starts up, as the voltage is lowered the current draw decreases as well - down to approx 18mA at 6V (all tested without backlight - just the meter itself).
don't know what such a meter should draw.. but 30mA looks a bit high to me.

Current is high because it's beeping. InERR is shown when leads are inserted into current sockets but range selected is not current.

[rob77]

Just curious, does this problem happen if you use a DC variable power supply set to 9V?  If you are doing this test, what is the current draw?

actually a good idea  tested it and it's drawing ~30mA at 9V and the meter starts up, as the voltage is lowered the current draw decreases as well - down to approx 18mA at 6V (all tested without backlight - just the meter itself).
don't know what such a meter should draw.. but 30mA looks a bit high to me.

Current is high because it's beeping. InERR is shown when leads are inserted into current sockets but range selected is not current.

it draws 30ma when powered from my bench supply actually works fine (except the high current draw). apart from inErr when the leads are misplaced it also shows inerr when the battery is drained out - it wont let you make bad measurement because of a drained battery.

[retiredcaps]

Martin's video on the 867 (yes 7, but should be similar to the 9) shows around 4.25mA current.  With backlight on, it is around 30mA.  Start around the 36:50 mark.

[rob77]

Martin's video on the 867 (yes 7, but should be similar to the 9) shows around 4.25mA current.  With backlight on, it is around 30mA.  Start around the 36:50 mark.

thanks a lot , 867 and 869 are basically the same meter, only difference is that 869 has few extra features and a bit better accuracy.
so definitely there is something wrong with my meter it draws ~ 30mA at 9V and 50mA with backlight on. took it apart but nothing obvious there. and i'm afraid that without a service manual or at least schematic diagram it's going to be hard. readings are spot on on DC voltage and resistance (haven't checked the others yet), so the main chipset and the reference should be OK.

[TheSteve]

Have you measured its input impedance to see if it is still correct?

[rob77]

my CEM DT-9935 LCR meter says ~13Mohm on volt range and ~40kohm on mV range when measuring the unpowered 869's input. measuring another meter's input yields very similar figures, so should be ok.
going to investigate further.... considering to buy a second bm869s meter to have a reference because i doubt i can find the service manual/schematic...

[retiredcaps]

and i'm afraid that without a service manual or at least schematic diagram it's going to be hard.

Three comments/suggestions.

1) If Dave can't get a schematic for his eevblog branded BM235, it is likely you won't either from Brymen for the 869.

2) I don't know how good these thermal cameras are or even if you can detect a 30mA draw with it, but if you have one, maybe it will show a hotspot?

3) I emailed Brymen asking for some component values for the 869 as per this thread.

https://www.eevblog.com/forum/repair/brymen-bm869-meets-high-voltage-in-real-world/

To my utter surprise, within 24 hours, I got a response.  You might want to ask them if they have seen this problem and what is the likely candidate.  Point them to this thread.  If the likely bad component is not proprietary, maybe they can give you a hint?

I sent my question above to info@brymen.com

[rob77]

i managed to find the little bastard responsible for the current leak. it was a small diode - apparently a protection to dissipate peaks or over-voltage into the battery. it's marked as D13 next to the COM jack. had to de-solder the com jack to have access with hot air to remove the diode.
apparently that poor little bastard died while doing his job... it's not rare that i measure 300V DC on a mV range or ohm range... or something stupid like that (because i tend to rush things )... so definitely i killed it, i just didn't realize the fault is there until i had to replace the battery and the meter thrown an error.  considering the current draw and the lifetime of a 9V battery it had to be few days before when i was repairing a small computer PSU.

[retiredcaps]

it was a small diode - apparently a protection to dissipate peaks or over-voltage into the battery. it's marked as D13 next to the COM jack

Good job finding it and more importantly documenting this.    I doubt I would have been able to solve this problem if it were my meter.  I learned something today.

[rob77]

it was a small diode - apparently a protection to dissipate peaks or over-voltage into the battery. it's marked as D13 next to the COM jack

Good job finding it and more importantly documenting this.    I doubt I would have been able to solve this problem if it were my meter.  I learned something today.

actually wasn't that hard.. i found approx 200ohm resistance between the + rail and the com jack (- of the battery is switched by the selector switch) , so the suspect was the protection circuitry. fortunately it's just a a 2 sided PCB with narrow (higher resistance) traces so it wasn't that hard to trace and find the low resistance point.

[pascal_sweden]

Brymen kit seems very fragile then! Shouldn't it manage to take over 1000V?

[rob77]

Brymen kit seems very fragile then! Shouldn't it manage to take over 1000V?

not at all, it's a very robust meter, i'm abusing it for a long period of time and this was the first time something noticeable happened. and actually it wasn't the input protection on the input jacks of the meter, it's part of the input protection of the chipset (dissipating spikes/over-voltage into the battery to protect the chipset). don't forget that on mV range you have the input resistor, PTCs, MOVs , few diodes as a last resort protection and then the ADC.... there is no 10meg resistor network in the path like on the volts range.

furthermore that psu i was mentioning was killing itself with spikes - the PFC circuit was killing the switcher with spikes, so no wonder it killed that poor diode in the meter while i was accidentally (actually pretty common for me ) "measuring" the 300VDC rail on the mV range (or ohms range).

[pascal_sweden]

Okey fair enough!

Is there any official Brymen supplier in Europe?

Even better if it is in Benelux or Scandinavia.

Any pointers here?

[rob77]

only source in europe i know of is www.tme.eu - i bought mine there.

[marber]

Is there any official Brymen supplier in Europe?

Even better if it is in Benelux or Scandinavia.

eleshop.nl sells some Brymen meters.

[Wytnucls]

Brymen kit seems very fragile then! Shouldn't it manage to take over 1000V?

not at all, it's a very robust meter, i'm abusing it for a long period of time and this was the first time something noticeable happened. and actually it wasn't the input protection on the input jacks of the meter, it's part of the input protection of the chipset (dissipating spikes/over-voltage into the battery to protect the chipset). don't forget that on mV range you have the input resistor, PTCs, MOVs , few diodes as a last resort protection and then the ADC.... there is no 10meg resistor network in the path like on the volts range.

furthermore that psu i was mentioning was killing itself with spikes - the PFC circuit was killing the switcher with spikes, so no wonder it killed that poor diode in the meter while i was accidentally (actually pretty common for me ) "measuring" the 300VDC rail on the mV range (or ohms range).

The meter must be able to handle 1000Vrms on all ranges, so higher spikes must have killed it.

[rob77]

The meter must be able to handle 1000Vrms on all ranges, so higher spikes must have killed it.

actually the spikes could have been over 1kV - the PFC was boosting into no capacitance (dried cap)... and the VSB switcher was killed instantly under slight load (TNY268 with 700V breakdown voltage), strangely the main switcher survived (UC3842
 + mosfet)
or the spikes were under 1KV but the diode was defective... (but the spikes must have been above 700V because they killed the TNY)

another point is - the meter basically survived (in terms of features) and the readings were spot-on, it was just leaking a bit of current   as i mentioned, i didn't even realize the fault till battery replacement.

[Fungus]

The meter must be able to handle 1000Vrms on all ranges, so higher spikes must have killed it.

actually the spikes could have been over 1kV - the PFC was boosting into no capacitance (dried cap)... and the VSB switcher was killed instantly under slight load (TNY268 with 700V breakdown voltage), strangely the main switcher survived (UC3842

On joe's testing thread the BM869S survived up to 5.9KV.

https://www.eevblog.com/forum/testgear/hear-kitty-kitty-kitty-nope-not-that-kind-of-cat/

[pascal_sweden]

How come that there are not more Brymen dealers in Europe?

Aren't there many dealers from Europe reading about Brymen on this forum?

It's a weird observation that it does not take up faster in Europe if it is such a great brand.

This makes me conclude that there must be other good alternatives next to Fluke and Brymen, that we don't know about yet

[joeqsmith]

That's correct but this is a 100uS FWHH exponential decaying pulse with a 2 ohm source.   Would a 1mS 2KV pulse damage it?   Would a 2KV MOT, I think we have that answer.      But I have supplied the Brymen (several times now) with 1KV DC and a 1KVp-p square wave with a +/-500V offset with the meter set to the voltage modes.   I have also put a 220V 60Hz full rectified signal into it and rotated the switch through all of it's positions.   Plus the grill starter.....   It's not the most robust meter I have looked at but it's still by far my favorite portable bench meter.   

The meter must be able to handle 1000Vrms on all ranges, so higher spikes must have killed it.

actually the spikes could have been over 1kV - the PFC was boosting into no capacitance (dried cap)... and the VSB switcher was killed instantly under slight load (TNY268 with 700V breakdown voltage), strangely the main switcher survived (UC3842

On joe's testing thread the BM869S survived up to 5.9KV.

https://www.eevblog.com/forum/testgear/hear-kitty-kitty-kitty-nope-not-that-kind-of-cat/