Veraxis
Active Member
(EDIT: the original title was: "A quick spiel: Dangerous unfused '830' multimeters and how to add fuses in easily", but it appears that most of these generic multimeters with "830" in the model are clones of the Mastech MAS830)
Hello all,
I was recently looking into finding a compact multimeter with a continuity buzzer to use for "away" jobs where I need to debug hardware but don't want to bring out my nicer and somewhat bulkier meter. Looking around online, I was able to find many listings for variants of an ultra-cheap "830" model multimeter, which in some cases can be had for as little as $3 including shipping. At such a low price, I brought two different ones-- an 830D and an 830L (with a backlit LCD), and decided to see which one I liked better. The listing also mentioned that it had a replaceable fuse for the lower current range, which is actually not always the case on these ultra-budget meters.
...Well, it turns out that last part of their description-- for both meters-- was a total lie. can you spot what's missing on the back of that board?
As it turns out, cheekily hidden underneath the piezo buzzer for the continuity test were the pads for the fuse holder, unpopulated and actually shorted out with a trace on the board (EDIT: it seems that the thin portion of the trace was meant to act as a fusible trace, but it is dubious at best that this would allow for an accurate fusing current, and would obviously not be replaceable. Credit to djsfantasi and Tony Stewart for this insight).
So, I took an exacto knife, scraped off the solder mask on the trace, made horizontal cuts across it down its entire length, then used a hot soldering iron to chip the trace up off the board. (The heat of the soldering iron works really well at de-laminating the trace off the PCB)
Finally, I added a bit of solder to the pads and tacked down a pair of fuse holder clips
Hopefully now I can feel a little better about bring this meter with me. If it weren't for this critical component they decided to leave out, these would otherwise be decent meters. The 10A range is still unfused aside from that piece of wire, but that isn't as unusual, and I could add a fuse to that too if needed.
Overall, I was disappointed but not exactly surprised to see that they had left out the fuse. Fortunately, they had the courtesy to leave the pads in so I could fix the issue. Even so, they are still pocket-sized, reasonably usable meters for what they are, and I won't feel too bad if I blow one up by accident.
Hello all,
I was recently looking into finding a compact multimeter with a continuity buzzer to use for "away" jobs where I need to debug hardware but don't want to bring out my nicer and somewhat bulkier meter. Looking around online, I was able to find many listings for variants of an ultra-cheap "830" model multimeter, which in some cases can be had for as little as $3 including shipping. At such a low price, I brought two different ones-- an 830D and an 830L (with a backlit LCD), and decided to see which one I liked better. The listing also mentioned that it had a replaceable fuse for the lower current range, which is actually not always the case on these ultra-budget meters.
...Well, it turns out that last part of their description-- for both meters-- was a total lie. can you spot what's missing on the back of that board?
As it turns out, cheekily hidden underneath the piezo buzzer for the continuity test were the pads for the fuse holder, unpopulated and actually shorted out with a trace on the board (EDIT: it seems that the thin portion of the trace was meant to act as a fusible trace, but it is dubious at best that this would allow for an accurate fusing current, and would obviously not be replaceable. Credit to djsfantasi and Tony Stewart for this insight).
So, I took an exacto knife, scraped off the solder mask on the trace, made horizontal cuts across it down its entire length, then used a hot soldering iron to chip the trace up off the board. (The heat of the soldering iron works really well at de-laminating the trace off the PCB)
Finally, I added a bit of solder to the pads and tacked down a pair of fuse holder clips
Hopefully now I can feel a little better about bring this meter with me. If it weren't for this critical component they decided to leave out, these would otherwise be decent meters. The 10A range is still unfused aside from that piece of wire, but that isn't as unusual, and I could add a fuse to that too if needed.
Overall, I was disappointed but not exactly surprised to see that they had left out the fuse. Fortunately, they had the courtesy to leave the pads in so I could fix the issue. Even so, they are still pocket-sized, reasonably usable meters for what they are, and I won't feel too bad if I blow one up by accident.
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