I've not seen one that needs a sound card to boot. They beep instead of playing samples. Well bullseye did and can't remember the other one.
It will boot reels then give alarms if no meters plugged in, but like other Tec they do different things depending on the fault and you get used to the wires combination of sounds and symptoms after spending hours or days trying stuff.
What size ROMs are you using for 777h? I'd go for 256 else the switch below the heat sink comes into play.
I won't spoil your fun by giving too much away as it's always good to work stuff out yourself... You know how to suck eggs?
With no ROM on board get reset high (something like 3.5v, not 5v) , 5.04(ish) volts to ram (4.5V is a fault but some try to run). Check address and data lines all pulse on the cro, and ram pin 18 looks good and it should boot with a program on.