The problem was the same on my test rig as shown below. All colours present but the video wouldn't sync to the monitor.
I cracked open the schematics and headed straight for the sync circuit section. Using my trusty logic probe I checked the LS32 at J7 the HSync* input on pin one was dead, pin 2 Vsync was pulsing away OK on my probe. The Hsync* signal comes from a 7474 at A9, Input signals on pin 12 looked good along with the horizontal timing on pin 11, but pin 9 was showing now activity and no high or low signal on my probe.
I piggybacked a new 7474 and the game synced back into life, the IC was removed, a new socket fitted and replacement IC inserted.
Another classic game lives to be played again. :)