Panel Meter with a Panaplex display

"Beckman" name in the lower-left corner.

A friend gave me a panel meter extracted from a broken RF power meter. The object was made by Gralex Industries and there is no information online about this model 475B-10.

I got it because of my interest in old display technologies, like Nixies and first generation LED displays.

This object mounts a Panaplex display, a technology missing in my limited collection.

The display is a Beckman SP-352 that features four 7-segment digits and decimal points.

I want to find a way to power up the meter, so that I know if the display is still working. It has a 0.2" card connector on the back, so it is easy to inject signals ... once that I will have reverse engineered the circuit!