The original 3VZ80 mezzanine board was powered by EPM240 dev board's 3.3V regulator.  The regulator is smallish and may not be enough to power the mezzanine board.  More importantly, only about 1/3 of CMOS Z80 can operate correctly at 3.3V, however my experiences have shown that most CMOS Z80 can operate correctly at 3.5V.  So I redesigned the 3VZ80 mezzanine board so it has a local adjustable 3.3V regulator. The local 3.3V is adjusted to 3.5V.  Mezzanine board operating at 3.5V won't affect the 3.3V EPM240 CPLD because EPM240 can tolerate I/O voltage up to 0.3V higher.

I tested 10 used CMOS Z80 that I recently purchased on eBay and sure enough at 3.5V and 16.7MHz CPU clock, every Z80 will boot into RomWBW and passed first few tests of zexall (zexall is a long test, but once a processor passed the first 3-4 tests it is likely to pass the remaining tests).