Multimeter repair brymen 786

[ss45]

I have a dead bm786.
Inserted new fresh batteries, rotate the switch, unfortunately no display..

Could anybody with knowledge guide where to start probing/ troubleshooting ?

Background : I m familiar with simple circuit, have another working fluke multimeter

Preliminary probing.
Output from linear regulator is normal about 3.5vindicated by yellow arrow in picture, There is 3.5v going into ic which I believe is a microcontroller.
No short found on any caps ...

There are the other 2 ics which I believe to be front end ADC ic and lcd driver, but since they are custom btc IC I can't find any datasheet (including the assumed microcontroller)

No sign of 3.5v going into ADC IC and lcd driver.. maybe supplied by different circuit or there is MOSFET gate failing somewhere... Hmmm...

Greatly appreciate your help

[jinu_j]

Re: Multimeter repair brymen 786

Hope you have eliminated the basic checks
- Fuse Check
- Issue with the knob (https://www.youtube.com/watch?v=IoRks5bJw8Y)


Are they all fine ?

[ss45]

Re: Multimeter repair brymen 786

Thanks for pointing out that.

Fuses are all ok.
The knob contacts are fine.

I have seen the video, but this multimeter doesn't even show any sign of life when I pushed and wiggled the knob forcefully...

[redwire]

Re: Multimeter repair brymen 786

For the Brymen 786/789 etc. I looked at pictures and it's a 4-layer board and a bit hard to follow all the traces.
I can suggest a few things to check. But first, never run a handheld multimeter from a bench DC power supply, always use the batteries.
On handheld multimeters input COM(-) at the banana jacks is floating and not the same as DC power (-) so it is too easy to blow the A/D if they ever touch.

Main voltage regulator U20 S-812C35 LDO output should be 3.5VDC and it looks like it's always powered on by the batteries.

Next is DC power switch Q18/Q19. This switches power to U4 LCD Driver HY2613C pin 5 and big tantalum C86 it looks like. Q19 base R158 goes to whatever turns it on.
So I would not rule out the crappy on/off switch just yet. Measure the voltages at Q18/Q19 and let us know if they have numbers.

[jinu_j]

Re: Multimeter repair brymen 786

Check this video. he bypasses the knob completely to test and direct external switch. You can use it to confirm there is no issue with the knob and that power is fine.
https://www.youtube.com/watch?v=UY9Myo5ngPQ

Check at time stamp 1:06:56 for the test

[redwire]

Re: Multimeter repair brymen 786

Is that the right video? The defect with the rotary switch was never divulged. Too many Brymen fanboys that won't say anything against it.

OP, measure mosfet Q18 gate voltage (goes to R155/R152 junction) and if it's near 3.5V it is OFF.

[CapLeaker]

Re: Multimeter repair brymen 786

Isn’t that the exclusive eevblog meter?

[redwire]

Re: Multimeter repair brymen 786

Yes the Brymen BM786 and BM789 are EEVblog branded. I would not buy one and actually can't lol.
Touted as "US$150 class"- last time I'd checked that's a crock. Prices incl. shipping:
From amazon.ca CAD $382-$432, today no listings at all for them.
From amazon.com CAD $277-$432, today $277 BM786 from EEVblog store (Customs fees not known) but you need amazon.com membership. No BM789's listed.
Simon's Electronics UK sells it on eBay for CAD $336 incl. shipping.

There's no sales/repair network for Canada and I think it's because Brymen OEM's for Fluke, GreenLee etc. that they are locked out.
Either that, or EEVblog makes money having no dealers. OP in Brazil I'm not sure who they have, it could be under warranty.

Issues so far have been the rotary switch, LCD contrast, a couple F/W bugs (autoranging) and you're screwed if it needs a firmware update - have to ship it across an ocean for that. So any repairs would be costly.
The quality is all fanboys ohhh ahhh but who uses an electromagnetic buzzer and plops it on top of the A/D pcb traces? So the buzzer cause malfunctions and Brymen gave out a little shield for it, of course a bodge because it's on the top of the buzzer. Everyday they design multimeters and bungling these things seems amateur.

I might be wrong here but it seems overrated and the quality intentionally on the cheap side. The low test currents 0.3mA sealed the deal this puppy cannot beat a Fluke or any other made in USA multimeters. Sigh.

[CapLeaker]

Re: Multimeter repair brymen 786

Yes the Brymen BM786 and BM789 are EEVblog branded. I would not buy one and actually can't lol.
Touted as "US$150 class"- last time I'd checked that's a crock. Prices incl. shipping:
From amazon.ca CAD $382-$432, today no listings at all for them.
From amazon.com CAD $277-$432, today $277 BM786 from EEVblog store (Customs fees not known) but you need amazon.com membership. No BM789's listed.
Simon's Electronics UK sells it on eBay for CAD $336 incl. shipping.

There's no sales/repair network for Canada and I think it's because Brymen OEM's for Fluke, GreenLee etc. that they are locked out.
Either that, or EEVblog makes money having no dealers. OP in Brazil I'm not sure who they have, it could be under warranty.

Issues so far have been the rotary switch, LCD contrast, a couple F/W bugs (autoranging) and you're screwed if it needs a firmware update - have to ship it across an ocean for that. So any repairs would be costly.
The quality is all fanboys ohhh ahhh but who uses an electromagnetic buzzer and plops it on top of the A/D pcb traces? So the buzzer cause malfunctions and Brymen gave out a little shield for it, of course a bodge because it's on the top of the buzzer. Everyday they design multimeters and bungling these things seems amateur.

I might be wrong here but it seems overrated and the quality intentionally on the cheap side. The low test currents 0.3mA sealed the deal this puppy cannot beat a Fluke or any other made in USA multimeters. Sigh.

I actually just bought one 4 weeks ago. The cheapest was to get it from Dave's store himself. Came fast with DHL. The BM-786 was ~ CAD$267 incl. shipping, import tax and exchange rate. So far so good! It's living on my bench. I am comparing it against my 20 year old Fluke 179. Never had a Brymen... so I'll give it a try. The latest Fluke acquisition I made was the Fluke 1587. So far so good with it too. Needed it for my new contract.
Greenlee is not selling rebranded Brymen's anymore. They are selling Flir DMM's now...
So far there is no issue with the rotary switch nor a lcd contrast issue with my BM876.

[redwire]

Re: Multimeter repair brymen 786

Congrats and let us know how it works. At first I was waiting for the H/W and F/W bugs to get ironed out and the thought of sending it Down Under for any of that was gross. Then people said Greenlee USA does work on them?
Check the F/W rev. you got, 78607 seems recent.

Uni-Trend is making for Amprobe, Milwaukee, Grainger, Minipa (Brazil), Voltcraft, Greenlee (USA), Digimaster, Urrea Surtek (Mexico), SPERRY Instruments USA, Tenma, PeakTech, Koban, CDI Electronics (USA), MCM, Di-LOG (UK), Klein Tools (USA), EXTECH Instruments, Southwire, UNI-T.

[ss45]

Re: Multimeter repair brymen 786

Thanks for your replies and input guys !
Will check it further this weekend ..
Definitely will post any findings

[CapLeaker]

Re: Multimeter repair brymen 786

Congrats and let us know how it works. At first I was waiting for the H/W and F/W bugs to get ironed out and the thought of sending it Down Under for any of that was gross. Then people said Greenlee USA does work on them?
Check the F/W rev. you got, 78607 seems recent.

Uni-Trend is making for Amprobe, Milwaukee, Grainger, Minipa (Brazil), Voltcraft, Greenlee (USA), Digimaster, Urrea Surtek (Mexico), SPERRY Instruments USA, Tenma, PeakTech, Koban, CDI Electronics (USA), MCM, Di-LOG (UK), Klein Tools (USA), EXTECH Instruments, Southwire, UNI-T.

I quickly checked the firmware, its 78607... I think Dave ships them out only with the latest firmware at the time of purchase.
Talking about buy american... read my Agilent DMM display issue thread... that really pissed me off. Figured wtf... spending twice as much on a new Agilent... I am going to try that Brymen... Even if the Brymen only last 6 years, I am ahead money wise compared to my Agilent. However I did buy a Fluke 1587FC very recent.
NEVER EVER buy an DMM with OLED display, unless you only want to have it for a couple of years.

[stj]

Re: Multimeter repair brymen 786

isnt fluke a holding of a financial investment group that has everything made in china now?

if i had to buy a high performance meter - money not an issue, it would be a uni-T 181

if i needed a meter for high voltage work, it would probably be a Hioki now.

[CapLeaker]

Re: Multimeter repair brymen 786

isnt fluke a holding of a financial investment group that has everything made in china now?

if i had to buy a high performance meter - money not an issue, it would be a uni-T 181

if i needed a meter for high voltage work, it would probably be a Hioki now.

I figured you would suggest these 2 brands. I considered Hioki too and would have bought one, but the convenience of the 1587 being able to do an insulation test and have a full DMM features like a Fluke 179 lesser the 10A current measurement, plus the remote (and I got a good deal on it), I pulled the trigger on that. It’s more useful to me. Others can’t do certain things and it requires me to bring multiple meters and I don’t really want to do that. I am lugging already too much stuff.

[ss45]

Re: Multimeter repair brymen 786

For the Brymen 786/789 etc. I looked at pictures and it's a 4-layer board and a bit hard to follow all the traces.
I can suggest a few things to check. But first, never run a handheld multimeter from a bench DC power supply, always use the batteries.
On handheld multimeters input COM(-) at the banana jacks is floating and not the same as DC power (-) so it is too easy to blow the A/D if they ever touch.

Main voltage regulator U20 S-812C35 LDO output should be 3.5VDC and it looks like it's always powered on by the batteries.

Next is DC power switch Q18/Q19. This switches power to U4 LCD Driver HY2613C pin 5 and big tantalum C86 it looks like. Q19 base R158 goes to whatever turns it on.
So I would not rule out the crappy on/off switch just yet. Measure the voltages at Q18/Q19 and let us know if they have numbers.

Sorry late, was busy, here is the measurement results

Q18 Pin1 0v pin2 3.2v pin3 3.5v

Q19 P1 3.2v p2 0.05v P3 0v

C86 0v

It looks like both q18 and q19 are PNP transistor. For q18 to turn on it needs to be pulled down by q19, and in turn q19 also need to be pulled down through 10k resistor connected to who knows what.
Here is the funny thing, the base of q19 was several mega ohm high, so whatever supposed to drive it is whether not responding, sleeping, or dead

Edit
Found the trace, that 10k resistor is driven by main ic.
See attached
Maybe the main UC is dead ? Or need reprogram ?
Either way, sad violin ......
Another meter bit the dust

[CapLeaker]

Re: Multimeter repair brymen 786

Or the display is dead. When you turn the meter on, the display should run with all the segments on, then it goes in what ever measurement mode it is selected to.
So it could be the MCU, the EEPROM, the display controller or the LCD itself. It's a tough repair. All you can do is to probe the MCU to see if it is doing anything at all or not with and oscilloscope and go from there.

[ss45]

Re: Multimeter repair brymen 786

Yeah .. it's not worth fixing...
Case closed

[retiredcaps]

Re: Multimeter repair brymen 786

Put it up for sale on ebay. Some eevblog fan may want to buy it for repair or parts?

[CapLeaker]

Re: Multimeter repair brymen 786

Before I'd do that, I put a thread into the EEVBlog... that's gotta generate some interest.

[retiredcaps]

Re: Multimeter repair brymen 786

Before I'd do that, I put a thread into the EEVBlog... that's gotta generate some interest.

He's already got a repair thread on eevblog with no help. See

https://www.eevblog.com/forum/repair/repair-brymen-786/