I check continuity from U850 pin from circuit diagram to U853 all ok I found no problem and all the 74F245 all been Replace for the fast Ram
The four 74F245 pin 2,3,4,5,6,7,8,9, they have no pulse which go to the fast Ram
The four 74F245 pin 1,11,12,13,14,15,16,17,18,19,they have pulse