Solid State Logic AWS 900+ Owner's Manual page 133

Appendices
The following problem highlights a Multidrop Bus fault and explains how the fault might be located. After
powering on the console you notice that all of Bay 2's channel strip LEDs are extinguished, and the switches do
not respond; all other bays are working correctly.
Once again refer to the AWS 900+ Control Block Schematic. From the diagram you can see that Multidrop Bus
data for Bay 2 is connected to socket PL2 on the 629645X1 CPU. Power down the console and remove the
channel meter from Bay 3 (refer to Replacing Modules on page A-10 for details). Located behind the channel
meter is the CPU. Remove the metal screen which surrounds the CPU and locate connector PL2. Remove and
then reinsert the connector to ensure that a sound connection is made. Re-assemble the console and check
the condition of the fault.
For the sake of the example we will assume that this did not resolve the problem. The next step would then be
to inspect the other end of the Multidrop Bus connection. The diagram shows that the data ribbon connects to
the CPUA socket on the 629640X1 Channel Backplane. Power down the console and remove Channels 15 and
16 as instructed in Replacing Modules (page A-10). Locate the CPUA connector and re-seat, then reassemble
the desk and check the fault.
Again we will assume that in this instance this did not resolve the problem. This leaves three possible causes.
The first is that the channel backplane has developed a fault. The second is that one of the channel strips in
Bay 2 has failed in such a way as to corrupt the data on the Multidrop Bus. The third is that the CPU card has
developed a fault with the hardware that processes Multidrop Bus 2.
The first cause is highly unlikely. The channel backplane contains no active components, only copper tracks,
and as such can be discounted. The second cause is possible – to determine this, remove the channel strips
from Bay 2, one by one, ensuring you power down the console each time, and check the condition of the fault.
If, after removing a module, the remaining channel strips start to function, then you have located the problem. If
you reach the last module and the fault still occurs, don't forget to swap the remaining module with one of the
others to ensure it is not the cause of the problem. If the fault still persists then the cause must be the CPU.
Once again, through a simple process of elimination, the cause of the fault has been located.
Unlike the Multidrop Bus which allows modules to be added and removed from the bus without effecting its
integrity, the Live Bus passes through one module to the next. Therefore the removal of a Live Bus module may
potentially disrupt other modules, depending on its position in the data chain.
When fault finding Live Bus problems the same principles can be applied, as the following example shows.
During a mix you suddenly notice that the channel meters in Bay 1 are all showing random patterns of
illumination.
As always the first step is to refer to the AWS Control Block Schematic. From the diagram you can see that Live
Bus data from the CPU passes through Bay 2 and 3's Channel Meter Panels before reaching the Meter Panel
in Bay 1. As the channel meters in Bay 2 are functioning correctly, you can rule out the CPU and Bay 3's Meter
Panel as potential causes of the problem. This leaves three potential causes. The first is that the data ribbon
connection between the two panels is not seated correctly. The second is that the input stage to Bay 1's Meter
Panel is faulty. The third is that Bay 2's Meter Panel has a faulty output stage.
A - 1 0
AWS 900+ Owner's Manual