I am trying to repair a fitness machine control PCB with an SMD component with unknown markings MVRB and LFNB. Could you please help me to identify this integrated circuit?

From the PCB, it is labelled RG2 so my guess is that it's a linear voltage regulator.

By testing with my DVM when 6V of a power supply are connected, I could read from the TP1 6V but on TP2 OV (should be 3.3V according to the labeling at the rear side of the PCB).

Also, these two test points are connected directly to the integrated circuit, so I believe that there is something wrong with it. I have discovered that pins 1,4,5 go connect together to the TP2 and pins 2,7 connect together with TP1. Hence, there is an electrolytic cap of 10uF connected to pin 2, which I believe should be the input according to some datasheets.

Therefore, I looked online to find the integrated circuit but sadly, I could not identify it because of the unknown markings. Please see the attached photos.

RG2 Integrated Circuit

Picture 1 is the PCB snapshot. Picture 2 is the integrated circuit

  • \$\begingroup\$ Thank you ever so much. \$\endgroup\$
    – Jonped
    Dec 10, 2023 at 17:31

1 Answer 1


Ti part marking lookup yields a result with LFNB. This leads to LP3981IMM-3.3/NOPB, which seems to be compatible with your pictures in terms of pinout.

LP3981 Pinout


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