Make sure no capacitor goo leakage from C7, C8, C9, C10 has spread and caused corrosion or shorts. If 20 pin PAL UI6 is socketed, note its direction, carefully remove it, and inspect all pins and socket metal for corrosion under magnification. Especially pin 18. Clean as required. Carefully replace. You may wish to do same for all other 20 pin PALs as sockets do become intermittent.

Turn board over. Look for R24 near J12 pin 10. Verify 75 ohms and continuity to UI6 pin 18, J12 pin 10. Locate all long black bar shaped parts designated by L followed by one or two digits. Using an ohmmeter, verify all these individual ferrite decoupling chokes have end to end continuity, and are not cracked.