Star Force (bootleg) repair log

Recently I've been sent a load of bootleg boards for repair, there was a Star Force  (a vertically scrolling shooter released in 1984 by Tehkan).It's a two stack set made by a CPU board :

and a VIDEO one :

Despite its age ( a sticker on CPU board says March 1985!) it was in good shape but faulty since on boot it was stuck on a static garbage screen.

Main CPU is a classic Z80 along with another same one for sound.Probing them revealed both was missing a proper clock signal on pin 6 which was stuck HIGH :

Looking at hardware and doing some tracing I quickly figured out the clock for both CPU was derived from the same circuit made by a 4MHz crystal plus the RC oscillator :

Both pin of the crystal were stuck, I traced them back to pin 1 and 2 of the near Toshiba TC40H004P which likely was faulty and forcing the crystal to not propery oscillate.I had no spare of it but, after found its datasheet, I realized it was CMOS HEX inverter :

 Hence I could replace it with a more common 74HC04 which I promptly did :

I applied power and board sprang to life, game was fully working with no issue :

Repair accomplished.