DMM Mastech MS8268

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This is a cheap DMM with all common function.

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It arrived in a box with a picture of another meter, because the box is used for multiple models. On the box is a comparison between the 5 meters in this series. This model has is the only auto ranging model, this also means it has more current ranges.

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It included the DMM, a pair of probes, a transistor/thermocoupler/capacitor adapter and a manual.

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The probes has removable tip covers. The CAT rating is marked on the tip and will change when the cover is removed.

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The plug is fully shrouded.

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This multi purpose adapter can be used for transistor tester, thermocoupler (Not on this meter) and for capacitor testing.
Supplying the transistor tester socket this way makes it safe (Build-in sockets are not safe).

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The tilting bale is easy to deploy and can hold the meter both for range switching and for pressing the buttons.

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The range switch is fairly soft with good clicks.

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Battery can be replaced without removing the sleeve.

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Meter without rubber sleeve,





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 number and what measurement is selected.
Auto means automatic range select.



Functions

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Buttons: Rotary switch:
Input

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The terminals are not deep enough to cover standard banana plugs, but they do connect. The light in the terminals is a very nice feature.



Measurements 1uF

A look at the capacity measurement waveform.

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Frequency input resistance.

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Tear down

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Four screws and the back could be removed.

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4 more screws for the circuit board

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And 4 clips for the range switch and lcd display cover.

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On the side with the voltage input R21A & R21B is the 10Mohm voltage input. The PTC1 is the ohm and capacity current output.
On the side with current input R32 is the mA shunt and R31 is the uA shunt, D5 and D6 is protection of the shunt resistor.
D2 is protection against reverse mounted batteries.
The meter uses trimmers to adjust the ranges (VT1, VR2, VR3, VR4). The meter chip is called SC9711.

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There is no parts on this side, only the lcd connection, the buttons and the range switch.

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All the input terminals is on an small circuit board together with a 10A fuse and the 10A shunt. Each terminal has a switch at the back, making it possible to detect when a banana plug is put into it.
The long fuse it not going to help much, the tracks on the circuit board are very close together.

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On this side the terminals can be seen with two leds around each of them. The current range PTC is also here. The chip is a PIC16F54 that controls the leds, depending on what plugs are inserted.

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A socket with a banana plug into it, as can be seen the switch part is moved away from the circuit board.



Conclusion

As usual this type of cheap meters do not have much safety and probably do not live up to its CAT rating, i.e. keep it away from high voltage and lots of current.
With that said it is a nice meter for occasionally hobby usage in the house and on the bench, due to the led indication of where to connect the probes and the resetable fuse, but the current ranges has a very high burden voltage, i.e. measuring at a few volts will not work correctly. The backlight cannot really be turned on, it can only be activated to get a single reading, because it turns off very fast.


Notes

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