Service manual

Service Manual
Thus a ROM failure (fault code 00000219 on an ARM 3
machine) will be displayed as:
short short short short 0
short short short short 0
short short short short 0
short short short short 0
short short short short 0
short short long short 2
short short short long 1
long short short long 9
Using the test link
The POST is normally only run after a power-up. If the
machine is reset after RISC OS has started, the POST
will be skipped. The action taken is dependant on the
value of the power-on interrupt bit in IOC.
You can force the self-test to occur (with no IOC read
performed) by making and fitting a test link (consisting
simply of a diode - IN4148 or similar) to the external test
connector. This is shown in Fig 5-1: The test link.
The external test connector is the 6 pin link LK4 on the
main PCB. It is situated near the four RAM upgrade
sockets, as shown in Fig 5-2: Link positions on main
PCB.
Fitting this link causes the tests to be run regardless of
the state of the IOC power-on interrupt bit. This may be
useful where it is not convenient to use the full test
adapters, and you require some positive indication of a
completed test sequence.
If the test link is fitted, the test result code is always
displayed (even if no fault is found). You can then read
the status bits in the least significant part of the result
word: currently, the only useful part of these status bits is
to indicate that an ARM 3 has been detected.
The screen will be set to green while the result code is
displayed: you can take this as a test pass if it occurs
after a proper sequence of purple and blue screens.
Fig 5-3: The display adaptor
Part 5 - Main PCB fault diagnosis Issue 2, June 1991 5-3