EEVblog Electronics Community Forum

Electronics => Repair => Topic started by: Kijo on January 13, 2020, 11:58:03 am

Title: EEVBlog BM235 Meter strange resistance fault
Post by: Kijo on January 13, 2020, 11:58:03 am

My BM235 Meter is having an issue in resistance/continuity mode. It never did this in the past and just noticed it when I picked it up a day ago.

If I switch from volts or the off position to resistance the meter gets stuck on what it thinks is a short, and keeps beeping constantly even when the leads are not touching. The display shows all 0 's and flashes. When I switch to resistance mode (without beep) it still says all 0's and attempting to measure anything fails. This also occurs when there is no probes attached. - as in it thinks there is a short when no probes are present!

However if I switch from the diode/capacitance side, it seems to work fine. I get the 0L display and I can measure resistance. This is until I touch both leads, and then its back in the same state again. Not sure why this happens but its proving annoying.

* Firmware is "d"
* Batteries are good - tested on my $10 Chinese meter
* Checked leads, they are fine
* Checked fuses, they are also fine
* Pulled apart meter and checked for any solider balls or dodgy components - none found (at least from what I can see)
* I keep the meter stored at my workbench, and can confirm it was not abused recently

Any help will be much appreciated!

Title: Re: EEVBlog BM235 Meter strange resistance fault
Post by: mzacharias on January 13, 2020, 03:02:39 pm

Probably an issue with the function switch contacts. There have been a few reports; not the same problem exactly.

I would service that switch assembly or return to the manufacturer for service - they have a three year warranty if memory serves.

Title: Re: EEVBlog BM235 Meter strange resistance fault
Post by: Kijo on July 29, 2020, 05:44:27 am

Thanks mzacharias,

I have been away (and stuck there) for a bit and hadn't got the chance to check this out. I was able to open up the meter and clean the switch contacts. everything looks good! Pics attached. Unfortunately the issue still happens! Here is a video of the issue:

https://youtu.be/NFgXKiKVJss

Also, the meter was gifted, so I don't have ny details on purchase date/etc - Do we go direct through Bryman?

Thanks,
Edward

Title: Re: EEVBlog BM235 Meter strange resistance fault
Post by: Kijo on July 29, 2020, 05:46:26 am

more photos of the board

Title: Re: EEVBlog BM235 Meter strange resistance fault
Post by: Kijo on July 29, 2020, 05:48:06 am

top

Title: Re: EEVBlog BM235 Meter strange resistance fault
Post by: Kijo on July 29, 2020, 05:48:56 am

bottom

Title: Re: EEVBlog BM235 Meter strange resistance fault
Post by: goaty on July 29, 2020, 08:15:45 am

I had a similar problem with a Voltcraft VC890 with EFM32 controller.
Problem was that a digital-I/O was dead on controller and it couldn´t detect the change when turing the range knob.
Maby an idea.