NorthStar HORIZON Manual page 55

and re-install the IC into the IC socket so that pin 3 of
the IC does not make contact with pin 3 of the IC socket.
Turn on the computer power and ground motherboard pin 43 by
shorting it to motherboard pin 50 with a piece of jumper
wire. This experiment will force the processor to
sequentially read every address in the computer
continuously, including the memory-mapped I/O locations that
turn on the drive motor (s) and select the drive (s). If the
motor(s) do not turn on, then trace backwards from the
signal MOTOR-SET/ to find out why. After correcting the
problem, remove the jumper, replace the IC's correctly at
locations 7C and 6C, and start over at the beginning of step
12. If the motor(s) do come on, that indicates that the
problem detected at the beginning of this step is probably a
result of the PROM program not being correctly executed.
Remove the jumper, replace the IC's, and proceed to part E.
E. Turn off the power and ground PRDY on the disk controller
board by shorting llA pin 7 to llA pin 8. Turn on the
power. The processor should pause immediately after
performing the auto-jump sequence just before executing the
first instruction of the disk controller PROM. The S-100
address bus A0-A15 (see the ZPB Manual Appendix 2 for bus
pin numbers) should contain E800H. (If this is not so, then
the problem is with the auto-jump circuitry on the processor
board.) The S-100 data input bus DI0-DI7 (see the ZPB
Manual Appendix 2 for pin numbers) should contain 0EH which
is the first instruction byte in the PROM. If this is not
so, then the problem is with the PROM circuitry on the disk
controller board, Trace backwards through this logic to
isolate the problem. After correcting the problem, remove
the jumper and start over at the beginning of step 12.
13. Next, power up the HORIZON with no diskette in drive #1
again. Approximately 12 seconds after the drive is selected
and the heads load, the motor(s) will turn off. The
processor at this point should be executing a tight JMP loop
indicating a read error. This can be checked by observing a
continuous stream of pulses on the disk controller board at
7C pin 6 (DI-GATE/).
14. Connect a serial I/O terminal to the standard serial
interface connector on the back panel. (See the Using the
Serial Interfaces section for a discussion of serial
interface cabling.) Be sure the terminal is grounded
correctly as described in the HORIZON Grounding section.
The terminal should be set for full-duplex operation and the
baud rate must match that of the standard serial interface.
55 North Star HORIZON Computer