DMM HoldPeak HP-770C

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This is a fairly cheap DMM with 40000 count display and lot of functions.

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It arrived in a universal HoldPeak cardboard box.

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Inside the box was a pouch with everything inside.

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It included the DMM, a pair of standard probes, a pair of alligator clips probes, a thermocoupler, a instructions sheets and the pouch.

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No tip covers on these probes that is rated for 1000V Cat III and 20A
This means the rating is wrong.

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The plug is fully shrouded.

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The alligator clip probes are without shroud and fairly short because they are designed to be used with the LC test function.

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The thermocoupler is encapsulated, this makes it useful for inserting in stuff, but not as good for measuring surface temperatures.

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The tilting bale has multiple position, including one as a hanger.

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On a smooth surface the meter needs two hands to turn the range switch.

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There is light in the range switch, it turns on together with the backlight.

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The metal ring on the back is a magnet, i.e. it is possible to attach the meter to metal surfaces.



Display

The meter do not show all display segments when turned on.

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Display during normal usage, it will show selected range and value.

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At the top is two leds used for the NCV, green when no field detected and red when a field is detected. The center position is a photosensor used to turn on the backlight on the display and the light in the range switch.



Functions

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Buttons: Rotary switch:

Input

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The capacitance and inductance input connectors. The are used with 4mm banana plugs.

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The shutters secures mostly that only the correct inputs are accessible, the capacitance and inductance are not covered by shutters.




Measurements 1uF

A look at the capacitance measurement waveform when measuring 1uF.

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Here is the inductance measuring waveform, the frequency is about the same on all inductance ranges.

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Frequency input resistance.

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When input voltage contains both AC and DC, the DC readout will be too low.






Tear down

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I had to remove two screws to open the DMM.

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To remove the circuit board there was 6 more screws.

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The shutter is controlled by a track on the range switch.

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This meter has a lot of chips, many of them are OpAmps: 2xLM358, TL062, TL072, a analog switch (4066), some Schmitt triggers / gates (7414, 4093) and a dual timer (4528).
The current shunts are near the 20A fuse (R10: 1ohm, R9: 9ohm, R8: 90ohm), there is two diodes to protect the current shunts (D7 & D8).
The 200kHz frequency range use the PTC and the transistor pair (T2 & T3) for protection, then the signal is going through a resistor and capacitor into the timer. This probably means that a analog voltage proportional to the frequency is generated and the meter measures that voltage to show frequency (Not very precise). Ohm output current is secured with the PTC and some transistors (T5, T6, T7). The voltage 10Mohm input is two resistors (R1 & R2: 2x4.5Mohm). The inductor measurement use some of the OpAmps and probably also the other chips.
There are many trimpots on the board to calibrate it.

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At the end of the circuit board is the NCV antenna, this an external part. There is 3 resistors (R77, R78, R79: 3x10Mohm) to maintain the potential on it.

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I had to remove 5 screws more before I could remove the display.

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This side of the circuit board has the power switch and transistor tester socket and at the top two leds and a LDR to control the backlight. The sockets for the LC tester is also here.

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Conclusion

As usual on cheap(er) DMM's the CAT rating is wrong, meter cannot be rated for 1000V and use 500V fuses. The transistor tester may also be problematic and the LC tester is very problematic.
Looking at the range switch it might look like the meter has a lot of ranges, but it do not. The inductance range is seldom seen on a multimeter and here it is missing some low ranges to check the uH inductors used in modern switchers.
The shutters reduces the risk of mistakes when switching between voltage and current, it is a good safety feature, but the LC inputs are missing them.
To supported as many different measurements as possible the meter has skipped a lot of ranges, this means it is often possible to measure stuff, but with lower resolution.



Notes

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