Frizz, you probably missed this line:
Perform the Preliminary Procedure under Hardware Diagnostic Tests and set the option switch at location 10D on the Main PCB as indicated in the test.
Which point to this:
Preliminary Procedure
Set the Self-Test switch to the on (up) position.
Ground the DIAGN test point on the Main PCB.
Set the option switches as indicated in the test procedure and momentarily ground the RESET test point on the Main PCB. If an unimplemented switch position is selected, LED 1, 2, and 3 on the Main PCB will all flash on and off about once per second. Also, the display will show the number of the test for Hardware Diagnostic Tests 10 through 26 (if the AVG PCB and display are working).
Consider the following suggestions:
If a significant number of tests are to be performed attach a small momentary on, normally off, pushbutton switch to the RESET test points.
Remove the high-score and bookkeeping nonvolatile RAM (NOVRAM) from location 1E on the Main PCB while troubleshooting the rest of the hardware. Each time the RESET test point is grounded, one of the RAM store cycles is used up. The nonvolatile RAM is rated for either 10,000 store cycles if the data is not changed, and 1,000 store cycles if the data is changed.