The serial number does end in 89-3. The computer does nothing but buzz until the reset buttons are pressed. The ROM seems to have 4 chip selects, two active high and two active low. The two "active high" ones are tied to +5 so they're always high. The two "active low" are high until the reset buttons are pressed, then there's data continuously on both. It seems like the CPU is executing code from the ROM. I think the problem might be with the RAM or the video circuitry.