A few years ago I bought 3 of these 4-30 v panel meters, one of each color , and mounted them into a box, each with a separate 9v battery and on off switch. I made a very small modification to remove 1 part so that it could have a 3rd wire connected and thus become a 0-30 v voltmeter using a separate supply to power it. However this week two of the 3 meters did not work – the blue one had 1 of the 7 segement drivers stop working, and the green one stopped measuring voltage, just reading 0v.

So I bought 3 new meters, to replace these previous meters. But I need to know how to modify these newest units to become a separately powered voltmeter.