Service manual

1. 8 channels of GP output lines each consisting of relay connections NC, NO and W
corresponding to 'normally closed', 'normally open' and 'wiper'.
2. 8 channels of GP input each of which is connected to the anode of an opto isolator input.
There is also an isolated return from the common cathodes and ground and 5V lines which
can be used to drive the opto isolators via external switches.
3. The external RS485 connection which can be used to control the rack.
J16 carries the following signals which go to the XLR connector PCB via J69:
1. Four balanced output signals. These are intended to be used for local monitoring and are
at a slightly lower level than the standard line outputs to reduce the amount of headroom
wasted when feeding amplifiers. 0dbFS from the console is output at +20dBu balanced.
There is no headroom control from the console relating to these outputs.
2. The AES sync input from an external sync source. This is a balanced AES audio line.
3. The AES sync output from the digital control module's sync circuitry.
4. A TTL word clock signal from the external Wordclk input.
5. Power to drive the Wordclk receiver and output buffer.
Power Supply
Mains is present on the backplane in this area. The two power supplies have independent
mains connectors each of which feed the power modules via J33, J34 and the two 15 way
power DIN connectors J13 and J14.
48 Volts from the two supplies is dioded together by D4 and D5 and filtered by L3 and C30.
The two 48V lines are sensed by the two comparators U2 and logically or'ed to give a single
n48VP_OK line for the digital control module.
The two 5VA lines are dioded together by D1 and D2 and filtered by C34. The two 5V digital
or VCC lines are dioded together by D6 and D7 and filtered by C33. The four 5V lines are
monitored by the comparators in U1 and diode or'ed to give a composite n5VP_OK line.
The 48V ok and 5V okay lines are also diode or'ed to give PSU1 and PSU2 okay lines for the
digital control module.
The +16V and -16V line have already been sensed in the power modules and the
composite 16V okay lines from the power modules go to the digital control module.
Because the +/-16V lines have diodes in line within the power modules the outputs of the
+16 supplies and -16V supplies are simply joined together on the backplane before
filtering by L1 and C31 and C32.
The returns of the various supplies are kept separate but are joined at the central earth point
which is in the middle of the two power module connectors on the backplane. A wire from
there goes to the rear panel earth lift switch where it can be connected to chassis or not as
required. For safety the chassis would normally be left securely connected to chassis at the
earth lift unless it can be guaranteed that the audio circuitry 0V has a secure path to earth via
another route.
Digital Service Manual
Issue 3 Page 37