Besides the suss tranny, how does the connector look? is that 'row pin' corroded/burnt out?
(maybe pull ALL the lamps out on that row, 1 of them might still be shorted in it's filament).

Might also be worth wiggling the lamp matrix connector and note of the row comes back or not.

Also, pull the IC out, and FORCE the ic socket pin hi/lo that drives into the tranny.
This will prove that the whole tranny/connector/wiring/lamps are all OK, then you can look backwards to the suss 74ls74 IC etc....

MM.