Brymen 807 -help me repair my first multimeter!

[de_light]

Just starting off in the world of electronics. Having read around carefully, I decided to try and buy a quality multimeter - lo and behold, a Brymen 807 appeared on Gumtree for a reasonable price. Looked good, seller stated it was in 'good order'. Drove down to buy it and excitedly opened it up to put some fresh batteries in.

Disaster.

Two old Duracells had exploded. Blue crystal in the battery holder compartment and the battery holder was FUBAR'ed. Negative terminal lead fell apart. The board itself seemed in reasonable condition: some minor corrosion around the + and - terminals. I cleaned it all off with IPA and replaced the x2 AAA battery holder and replaced the case.

It worked! - kind of. There was an intermittent fault - turning the rotary selector led to all sorts of strange things. The buzzer rang continously (? a short). The selectors flicked on and off - acting all weird. Now, with the multimeter out of the casing and unscrewed, it works fine!! The minute I screwed it down with the casing on - problems occurred.

To cut a two hour story short, I decided to take off the rotary selector switch. And there lay the problem, I think. There was some corrison under the switch, adjacent to the battery terminals. I used some IPA and scrubbed off the corrosion on both the board and the golden selector pins.

Here lies my first problem. During my excitement at potentially finding the fault, I scrubbed the gold contacts with a toothbrush, not realising they were held in only by friction.


I can't remember how they went in the first place!! I have a gold connector that I can't find a home for. Can anyone help?

[de_light]

Wow! Fantastic customer service from Brymen. Gary from Brymen replied to an email I sent within an hour attaching the correct rotary switch contact placement, which works. Below for future reference.



Think I've also found the problem. The device seemed to be intermittently shorting - when the case was on, if you pressed hard on the rotary switch, the display would change and the buzzer would sound. It just seemed like it was shorting somewhere. On opening up the case, it seems like a spring is missing to prevent contact with the foil and the buzzer.

[de_light]

Unfortunately, problem isn't fixed.

Everything now works ok when the case is closed....apart from

The buzzer sounds continuously in all modes except mA and uA.

[goaty]

Maby it is a problem with the sockets detecting a plugged cable where there is none ?
Check if both halfs of the sockets do not touch when no plug inserted.

(They even call it Beep-Jack(TM) in the brochure)

[retiredcaps]

Two old Duracells had exploded. Blue crystal in the battery holder compartment and the battery holder was FUBAR'ed. Negative terminal lead fell apart. The board itself seemed in reasonable condition: some minor corrosion around the + and - terminals. I cleaned it all off with IPA and replaced the x2 AAA battery holder and replaced the case.

Anytime you have battery leakage and still have strange or intermittent problems, it's always a good idea to dunk the entire pcb, minus the lcd, fuses and battery, in an IPA bath and scrub with a clean toothbrush.  An ultrasonic bath is another alternative.

Let pcb dry thoroughly overnight or use a small pc fan to get it completely dry.

Then, retest your functions.  Many times, they will disappear.

Try also cleaning the input sockets as per

http://mrmodemhead.com/blog/gallery/fluke-189-clean-up/

[de_light]

Thanks for both of your replies. I have carefully cleaned off any corrosion (there wasn't a great deal, to be honest) under 10x magnification with a needle and have scrubbed it with a toothbrush in IPA. I have also cleaned out the multimeter sockets with a cotton bud in circuit cleaner. I have also run it through an ultrasonic cleaner, two 10-minute cycles.

I shall reassemble when I get home and see what happens.


I think the clue is something wrong with the speaker connection. With the board screwed down firmly, the buzzer sounds continously in all modes except uA and mA. Continuity doesn't work (as the buzzer is on constantly). If I slightly loosen the board screw where it connects onto the case, the buzzer doesn't sound....unless you press down on the case firmly where the buzzer springs lie. On the board itself are two pins that are soldered onto the buzzer springs: these are labelled BZ1 and BZ2 (marked in image). If you short, these two pins with a tweezer say, the device 'panicks': the LCD screen flashes randomly and turns off. Not sure of the significance of this.

[de_light]

Well, update time. It is so much better than what it was before. That intermittent speaker fault has gone. Now, only if you press a little too hard on the selector switch it can flick between resistance and mA and the buzzer squeals.

I put it through an ultrasonic cleaner x2 and then under 10x magnification, picked off any specs of corrosion I could see. I also cleaned all the input jacks with cotton tips and alcohol as described.

I'd be really interested to hear if anyone has any ideas on how to fault-find the problem with the rotary selector. It would be great (even just for my experience).

[garrettm]

Nice work on the repair de_light!

I think my first multimeter was a Wavetek 38XR. Picked it up used for maybe 25 USD. Great DMM for the price. I eventually sold it to some fellow in Australia come to think of it. Small world.

Now you know why most folks avoid using alkaline batteries! A lithium or NiMH 9V AAA is a much better choice, especially considering that they are rechargeable. Though the NiMH can still leak if left discharged for a prolonged period of time.

I'm not familiar with Brymen meters, but it might be possible that there is too much "play" in the selector switch, allowing it to wobble or even compress the spring contacts a hair too much. If it takes considerable force to cause the erroneous behavior I wouldn't worry about it, but if even light pressure from normal use causes the fault I'd look into the alignment of the switch.

Edit: Didn't realize these used AAA batteries.

[de_light]

It's not bad at all. It is perfectly workable and really doesn't cause a massive problem. The beep-jack function is quite good and it shows there is some 'scratchiness' on the rotary contact where there is corrosion (at the 7 oclock position). But that's life - the main thing is that it has gone from non-functional to functional!

I've put some eneloops in.

[rsjsouza]

Goos job on the repair, and Brymen customer support is indeed stellar!

As mentioned above, perhaps the corrosion increased some space on the mechanical switch or the surrounding PCB. I can't feel any vertical juggle on the rotary switch of my BM857 (same housing and rotary switch as the 807). I suspect you did that already, but perhaps re-inspect thr board for micro fissures around the rotary switch PCB contacts?