Oops, there is a Zener on the PCB; didn't notice that before smile I just plugged the chip in and played a few games, and it still seems to work fine - lucky me. But the sound is annoying as hell!

With 6 AA batteries installed, I measure 6-7 volts between VSS and VDD at the chip depending on how many LEDs are lit. The 444L data sheet says standard operating voltage is 6.3 max, with an absolute max rating of 10V at any pin with reference to ground. So I guess it could handle 9V for the 2 minutes or so that I dumped the ROM.