AWS 924-948 - Solid State Logic

G: TroubleshootingAgain for the sake of the example, we will assume that the level on the Track Bus meters was different. Halving the signalpath again, de-assign Channel 24 from the Track Busses, route the same signal to Channel 23 and assign it to Track Busses1 and 2. Can signal be heard on the right monitor? If it can then you have identified in a matter of minutes that Channel24 has a faulty Track Bus output stage. If audio cannot be heard, then you have identified that the 629919X1 Track Buscard is faulty.The next step in either case would be to follow the module removal instructions below and re-seat the module in its slotto ensure that a valid connection is made. Once re-seated, test the signal path again. If there is no change, a replacementwill be required.Control FaultsControl faults will typically result in either the corruption of display information, or the failure of encoders and switches.The majority of the console’s display and control functions are performed by the 629645X1 CPU, which is located behindBay 3’s Meter Panel. The CPU uses two methods of control. These are Multidrop Bus and Live Bus. Both busses arebidirectional and carry control data, such as switch presses, to the CPU as well as display data, such as LED illuminationcommands, to the displays.Multidrop Bus data is used to control all of the console’s audio processing modules, these are the 629921X1 ChannelStrips, 629651X1 6-Track Select, 629652X1 2-Track Select, 626653X1 Gain and MDAC Control, 620654X1 MonitorOutputs, 629918X1/2 Dynamics, 629918X1/2 8-Track and Aux Bus, and the 629928X1 Compressor. All other panels arecontrolled by the Live Bus. Referring to the AWS Control Block Schematic you will see that four Multidrop busses, oneper bay are used. The Multidrop data from the CPU is connected to each of the channel backplanes and the centre buscardusing a 20-pin IDC ribbon connector. The audio processing card then sit on this bus, sending or receiving data as required.The following problem highlights a Multidrop Bus fault and explains how the fault might be located. After powering on theconsole you notice that all of Bay 2’s channel strip LEDs are extinguished, and the switches do not respond; all other baysare working correctly.Once again refer to the AWS Control Block Schematic. From the diagram you can see that Multidrop Bus data for Bay 2is 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 the following page). Located behind the channel meter is the CPU. Remove the metalscreen which surrounds the CPU and locate connector PL2. Remove and then reinsert the connector to ensure that asound 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 inspectthe other end of the Multidrop Bus connection. The diagram shows that the data ribbon connects to the CPUA socketon the 629640X1 Channel Backplane. Power down the console and remove Channels 15 and 16 as instructed inReplacing Modules (on the following page). Locate the CPUA connector and re-seat, then reassemble the desk andcheck the fault.Again we will assume that in this instance this did not resolve the problem. This leaves three possible causes. The first isthat the channel backplane has developed a fault. The second is that one of the channel strips in Bay 2 has failed in such away as to corrupt the data on the Multidrop Bus. The third is that the CPU card has developed a fault with the hardwarethat processes Multidrop Bus 2.The first cause is highly unlikely. The channel backplane contains no active components, only copper tracks, and as suchcan 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, theremaining channel strips start to function, then you have located the problem. If you reach the last module and the faultstill 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 causeof the fault has been located.Appendices Page A-14AWS 924-948 Owner’s Manual