PROSTER BM4070 Digital LCR Tester

[jebem]

I got this BM4070 some years ago.  I believe it is still available on several web shops.

This tester comes from an era when a linear potentiometer was needed to adjust for Zero (only for on Capacitor ranges).

It needs now calibration on the higher capacitance ranges, as the readings are far off to be trusted.
It uses trimmers for calibration. Just need to remove the back cover by undoing four screws.
The daughterboard PCB  has nine trimmers labeled as follows:

VR1   200pF
VR3   20-200uF
VR4   2000uF

VR5   200uH
VR8   200uH-1
VR6   2mH
VR9   2mH-1
VR2   20mH-200mH
VR7   2-20H

I am waiting to get my new ZT-DQ02 LCR tester to have another tester to compare readings.

Meanwhile I opened it for inspection and took the opportunity to take pictures.
There are two PCB's. The main board with reference BM4070 REV:2.0 220106 (2022-JAN-06), and the daughterboard is BM4070x REV:2.1 211210 (2021-DEC-10).

Main board - Main components:
IC1   BLOB      MCU - 44-PIN IC
IC2   14053BG      16-PIN MC14053B Triple SPDT Analog Multiplexers/Demultiplexers
IC3   TL062G      8-pin TL062G Dual Low Power JFET OpAmp
Q1   S8050      TO-92 S8050 NPN BJT 2W 1.5A 40V
Q1   S8050      TO-92 S8050 NPN BJT 2W 1.5A 40V
Q3   J6              SOT-23 SMD S9014 NPN BJT 0.2W 0.1A 50V
Q4   2A              SOT-23 SMD MMBT3906 PNP BJT 0.2W 0.2A 40V
D3-D7   M7      1N4007 1A 1000V Si DIODE
D8-D12   M7      1N4007 1A 1000V Si DIODE
R27   PTC              1500R
VR10   Zero Adj   1MR Linear Pot

Daughterboard - Main components:
IC4   072C      8-PIN TL072 Dual Low Noise FET OpAmp
IC5   072C      8-PIN TL072 Dual Low Noise FET OpAmp
IC6   4093BF   14-PIN CD4093BF Quad 2-Input NAND Schmitt Trigger
IC7   14066BG   14-PIN MC14066B Quad Analog Switch/Quad Multiplexer
IC8   OPA1612   8-PIN OPA1612 Dual High Performance Bipolar Audio OpAmp

The BM4070 runs on a 9V dry battery and consumes around 10mA independently of the selected scale.
A value too high for such a small battery imho.

[jebem]

Additional pictures:

[Stray Electron]

  Thanks for the review.  I was just gifted one of these yesterday and I just tried it out this afternoon.  It seems to work very well for $37 meter! But I was curious about what frequency they tested inductors and capacitors on. I looked in the meter's manual and it doesn't says anything about it so I looked up the specs on Proester's website and they claim that it test at "99.99Hz/999.9Hz/9.999KHz/99.99KHz/999.9KHz/5MHz".  Do anyone know anything about that? My guess is that they must change frequency with each range on the meter. 

[Martin72]

Do you have an oscilloscope?
Then you can measure it.

My guess is that they must change frequency with each range on the meter.

That will also be the case; for example, pF is difficult to measure at 100Hz, so the measurement frequency must be higher.