Service manual

the processor data bus. If this functions correctly it is close to a guarantee that the whole system is functional.
9.2 A test tape is available which exercises most of the functions of the QL and is a useful initial diagnostic tool. See Section 3 for details.
FIGURE 1.3 QL BLOCK DIAGRAM
FIGURE 1.4 QL CIRCUIT DIAGRAM (Issue 5)
FIGURE 1.5 QL CIRCUIT DIAGRAM (Issue 6)