DMM Mastech MS8216

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This is a small pocket DMM with voltage, frequency, ohms and capacity.

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The meter was in a clamshell pack. On the back is a the specifications.

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In the pack was the meter and a manual in English.

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The probes are small and they are not round, but ellipse shaped.

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The probes are directly connected to the meter, no plugs and sockets.

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The range switch is easy to turn, but the detents are not very strong and it is very easy to place the switch between ranges.

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A pouch is included.

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Two screws must be removed to get battery access.



Display

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The above picture shows all the segments on the display.

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Typical display during usage, it will show the selected range and value.



Functions

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Buttons: Selection of Rel and Hz/duty will disable auto ranging and it stays disabled

Rotary switch:

Input

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This meter only have a red and black probe coming out, no other connections.


Measurements
1uF

Capacity measurement waveform.

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Frequency input resistance in voltage frequency position, V and mVDC is similar.

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Frequency input resistance in voltage AC position.

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Lowest capacity range is sometimes out of tolerance (Up to 8%) and next time I measure the same capacitor it is inside tolerance.



Tear down

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I had to remove two screws, to open it, this is also required when replacing batteries.

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The battery holder is for two button cells.

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I had to remove 6 screws before I could get the circuit board out.

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The buzzer is mounted on the front plate.

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On this side there is only two capacitors and holes for adjusting the 3 trimpot (VR1, VR2, VR4).

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On the input is a PTC (R24), it is not used for all ranges. The main input resistor (R21 & R'21 2x5Mohm) goes directly to the multimeter chip. My guess is that the input protection is a single transistor (Q1), it looks like the 5 diodes (D3..D7) is used for coding range switch to multimeter chip and the two other diodes (D1 & D2) may be rectifier circuit for AC measurement where VR2 is used to adjust it with.
The multimeter chip (IC1 CS7721) handles everything in the meter.

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Conclusion

The meter is specified at 600V, but the ranges can only handle 250V in overload.

The meter has about the expected functions for a pocket meter without any current ranges. There is a few problematic areas with it: Range switch must be carefully placed in the correct position it do not snap into position, buzzer is difficult to hear, duty cycle is low performance and the lowest capacity range is not completely reliable.



Notes

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