It seems like large-screen cheap meters are really catching on. [TheHWcave] does a very detailed review of a KAIWEETS KM601, which is exactly the same as a few dozen other Chinese brands you can get from the usual sources. You can see the review in the video below.
If we learned nothing else from this video, we did learn that you can identify unmarked fuses with a scale. The fuses inside were not marked, so he wanted to know if they appeared to be the right values. We would have been tempted to just blow them under controlled conditions, but we get he didn’t want to destroy the stock fuses until after testing.
The teardown and analysis are quite detailed with a few interesting tidbits, especially how the current probes route through the board. One interesting observation is that the controller chip inside has one-time programmable memory and he speculates that calibration data is programmed into it once. If true, this would make the meter unlikely to have any way to field calibrate it. Of course, the meter may calibrate itself on startup using some known internal reference, but it is hard to tell since the datasheet for the part doesn’t seem to be available.
There are a few surprising details inside. There are two independent processors inside. One may be for the temperature function. The soldering workmanship — mostly removing excess solder — left something to be desired. But the meter works well enough for its price point, although he does suggest getting a better set of probes.