Elenco M-2666K Multimeter Kit teardown

[Robomeds]

Is it really a teardown if you just built the thing?
Anyway, a while back I had a build your own DMM kit based on the 830 meter design.  Recently I found this more advanced kit and thought it would be fun to put the thing together.  So in the end I have a meter that I won’t use but was fun to assemble.  For those who are interested let’s take it back apart. 

Before I do let’s review the outside of the thing.  Well it’s cheap plastic.  It does have a protective boot but I’m not sure if offers that much protection.  It’s rather stiff but I guess it does help hold the thing together.  Case integrity is optimistically handled by just 2 screws!  Those two screws hold the battery door on and hold the bottom half of the case together.  The top half is held by to snaps. 

Function wise I guess this is decent enough for a manual meter.  Kind of that old 1980s lot’s ‘o ranges manual stuff.  For a 2000 count meter it seems to have a good range of measurement ranges.   However, it lacks things like hold, relative or anything other than a power switch.  It does have a weak continuity test which is handled outside of the main IC.  The display is at least easy to read with very good contrast and well formed digits.  However, the very small print on the range switch might negate that ergonomic advantage.  The tilting bail is cheap feeling but I guess it works. 

[Robomeds]

On to the inside. 
Well the company can be forgiven any poor soldering or haphazardly inserted components as they didn’t assemble any of that.  Clearly there are lots of groups of resistors used to make the various ranges.  The opamps are used for the capacitance testing and… well I didn’t actually read the theory of operation part of the manual so some other stuff too.  The manual for these things can be found on line for the curious. 

Accuracy is stated as 1% VDC.  I was able to trim it to match my BK 5390 (.025%) but that was at one temp etc.  I’m sure it won’t hold that accuracy over time and conditions. 
What about safety?  Well the safest way to use the meter is to avoid it.  Actually it’s not quite that bad but it’s still very bottom of the barrel.  You can see there are no routed channels in the PCB and no blast shields.  Heck, why worry about blast shields when the 20A terminal isn’t fused.  The mA range does at least have a glass fuse and I see a PTC for over voltage protection.  The case is made out of plastic with no sharp edges  and the wire test leads are insulated.  I don’t think you can get better than that. 

Would I do it again?  Sure!  I think these old kits are fun to assemble.  I didn’t really learn anything but I wouldn’t learn anything by putting together a puzzle either, it’s still kind of fun. 

[retiredcaps]

Thanks for sharing your project.  At least this multimeter has an on/off switch so you can leave the rotary switch in your most "used" position.

I have a manual meter that has 30 rotary positions with no on/off switch.  It always draws 5 to 6mA which suggests < 100 hours from a 9V battery.  Needless to say, I don't reach for it first, but I keep it around for learning purposes.