Acorn BBC Master 128, Service Manual

Page: 52 / 87

Master Series Service Manual
5 Have voltages outside the supply range been applied to any of the
pins? If so, the VIA may have been damaged.
Note: this could arise if a cable is left connected the the User Port
and the other end is, for instance, left trailing across a carpet.
7.11 1MHz bus
1 Is there anything in the configuration system that would cause the
1MHz bus to be deselected? For example, this would happen if the
computer were configured to power up with a floppy disc drive as the
default rather than a hard disc, therefore making the hard disc seem
not to work.
2 Ensure that the software has not selected the internal pages &FC
and &FD.
3 As with any straightforward parallel data bus, any faults with this
have to be found by methodical checking of all connections.
a) Ensure the remote equipment is not at fault (if possible).
b) Ensure the cables and connectors are in good condition and are
correctly assembled, i.e. cable clamps are fitted and effective.
c) Ensure that any non-polarised connectors are correctly inserted.
d) Cables longer than 1m should in general not be used.
e) Check that each and every connection is correct as per the circuit
diagram.
f) Check that the READY signal from the I0 Controller (IC15 pin 17)
goes to both the CPU (IC14 pin 2) and the Peripheral Bus Controller (
IC21 pin 11).
g) Check that the FIT connection from the I0 controller (IC15 pin 38)
goes to the PBC (IC21 pin 5).
h) Check that all address connections to the Memory Controller (IC20)
are correct.
i) Check that the two data bus connections to the I0 Controller are
correct (IC15 pins 18 and 19).
7.12 The Tube
1 Check 3 a) b) c) d) e) f) g) h) and i) as for 1MHz bus above.
7.13 Internal co-processor
7.13.1 Not being recognised.
1 Is the configuration status correct?
2 Are the two connectors correctly mated?
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