EEVblog 1520 - Troubleshooting a Faulty BM786 Multimeter

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Looking at a faulty returned BM786 multimeter.
Warning: Some components were harmed in the making of this video.

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#ElectronicsCreators #Repair #Multimeter

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LOL. EVERYONE including myself missed a major goof in this video. Can you spot it? It's not the fault, but it's something I was wrongly assuming. I can't believe not a single viewer picked me up on it!

EEVblog

My 22 year old Fluke 177 and 15 year old Fluke 85-V still has the plastic film on the display. I enjoy the fact that it drives people nuts.

kevincummins

Repair videos are always welcome, thank you. Always good to learn about troubleshooting electronics.

bertblankenstein

Dave: A quickie test I use on stuff like this where you are not sure the micro is clocking (bad Xtal, no power, whatever...) is to hold a small battery operated am radio tuned to a dead channel next to the device and turn the device on. If the device is clocking you will pick up a bunch of "hash" in the AM radio. Not 100 % foolproof, but very quick and easy to do and it gives some direction to your troubleshooting...

Vincent_Sullivan

About those protective films. I try to keep them on as much as possible (well unless they are annoying). I remember that my Nokia 3310 had the protective film during all the years that I used it (I nicely cut off the smal lip to peel the film off so that it would stay on nicely).
A real funny story is when I bought a plastic cutlery tray for my kitchen drawer I saw that the surface started to look bad after a few years and was about to throw it away when I saw that it actually had a protective film on it leaving me with a brand new tray after all those years (peeling off that film was ... omg, best day of my life).

ppdan

0:40 A while back I got a magnifier for viewing DSLR sensors, and it seemed to have mediocre (but usable) optics. Then I peeled the film off!

michael.a.covington

For whatever it is worth, I would clear that debris between the multimeter chip pins. It takes pretty much no effort and removes that small possibility. Maybe my ocd, but I'd do that.

bertblankenstein

Thanks for sharing the journey, because the journey is always worth it! I know I learned a few things, got to flex my grey matter and find out that I was right a couple times during your journey. And that I was wrong a couple times as well, too!

stevedaenginerd

Been using one of these for over a year now, well worth the money. No hesitation to probe around the 480v sprinkler systems we use, the 240v wells, etc and it still has all the features for the electronics stuff

trapperjohn

At this point of the troubleshooting without having a replacement chip I would suggest trying to reflow the BTC chip, just in case one of the pin is not soldered properly

Chris-xutf

It failed because they didn't take off the protective film. That'll teach them! 😉

Niei

When you suspect a bad mosfet, or any transistor, it's prudent to check the voltages at the terminals first of all. That will reveal quickly if it is faulty or not. Before changing components and potentially lifting traces.

MatthiasWelwarsky

We learn more from how you troubleshoot, than from you repairing this one fault on this one device. Much appreciated Dave

Fake_Blood

Drinking game: take a shot after Dave says "schematic"

Rorschach

I think the U1 "microcontroller" you are pointing to is actually the HY3131 DMM front end (48 pin). The NCs pins seem to line up. The pins you pointed to are AGND, REFO and VSSA on the front-end. The location of Xin/Xout seem correct and the HY3131 spec sheet specifies that 4.9152 Mhz Xtal. Perhaps U16 (64 pin) next to the buzzer is the microcontroller? Maybe U16 is a HY16F 32bit microcontroller?

phil