Digital power meter mod for voltages down to zero

[ccktek]

No hardcore engineering here, just a tip that may be useful to others.

The widely available D85-2058 panel power meter seemed ideal for a recent variable isolation transformer project.  There are several cosmetic variants of the meter that may have very similar or identical circuits.  The D85-2058 operates down to 40V, below which the display is extinguished.  I wanted to display voltage down to 0V.  That necessitated separating the 60Hz fixed and variable feeds to the D85-2058, accomplished by cutting a trace on the PCB that runs from the hot side of the mains input to a string of 510K resistors.  The variable voltage from the Variac wiper is then fed to the resistor side of the cut trace while the fixed 120V supply to the display is left intact.