HP98780 monitor graphics PCB

Does anyone here have an HP98780 (enhanced mono monitor for the HP9845B) easily to hand, and if so, could they do a little electrical test on one of the PCBs : Remove the top cover (4 screws), the screening cover under it (4 more screws). the 2 board hold-down strips (3 screws each), and the 2 screws holding the heatsink pillars from the rightmost board to the right side panel (directions given with the screen towards you). Pull this board out. When putting it back, put a little silicone grease on the ends of the pillars. In my monitor it's a 98780-66552 Rev B, I am particularly interested if you have that version... Anyway, the test : Check for continuity between pin 7 of U53 (this is a 74LS157 mux chip) and pin 2 of U55 (a 4116 or 4816 DRAM). The reason is that on my board, these 2 pins are not conencted, although the other outputs of that mux -- and of 3 other similar mux chips -- do go to the DIn pins of the RAMs. The 'missing' one would be bit 6 (of a 16 bit word), and I can't for the life of me think of a good reason why it should be different. I wonder if I have a cracked trace in the board somewhere (this is a multi-layer board so I can't check by eye). Thanks in advance -tony