Mackie d8b v3, Service Manual

Page: 13 / 117

13
ANALOG SYSTEMS
The analog circuits used in the d8b should be familiar to anyone with experience
servicing Mackie products. The 12 Mic Pre’s are the same circuit which is used in the
SR40•8. The line amps use Mackie’s ‘unity plus’ architecture.
DCA BOARD
As the name suggests, the DCA board contains Digital Controlled Amplifiers to control
the level of analog signals in the console’s monitor section. The DCA board also
contains an analog switching matrix to select and route monitor signals. The Brain Board
controls switching and level functions on the DCA Board. DCAs are controlled by a serial
data line. Analog switches are controlled by SIPO shift registers, except for TALK and
PUNCH which are controlled directly by the Brain board’s CPU.
POWER
POWER SUPPLIES
There are three power supplies within the Remote CPU chassis. A standard PC power
supply for the Pentium Motherboard, a +5V, 100W OEM switching supply for the console’s
digital functions, and an analog supply for the console’s analog functions.
The PC supply and the OEM supply should be treated as ‘black boxes’ and swapped
if bad. The analog supply is nearly identical to the design used in the SR24•4,
troubleshooting should be fairly straightforward.
POWER DISTRIBUTION
In the console, power is sent from the Power Distribution Board (111) to the Brain, DSP,
Backplane, and Analog I/O boards. These boards then distribute power to the remaining
boards.
Note: there are many bypass capacitors used throughout the console. If one of the
power supply rails is low or intermittent, one of these may have shorted, but it not an
easy thing to find which one. It will be a great help if you have a low impedance ohm
meter. You should then be able to narrow in on the offending cap or ferrite.
NOTE:
The d8b keeps the same jumper designations for all PCBs, Hurrah! So J35 on the output
board is also J35 on the Brain board. See the connectors chapter for complete details of
every connector and pinout used in the console.
If the d8b has optional I/O cards installed, use a slotted screwdriver to make sure the
installation screws are tightly secured, and not just finger-tight.
NOTE: The Bus numbers as written on the schematics for the CODEC and DCA
board are reverse numbered by the software. So Bus 1 on the schematic is
really Bus 8, Bus 2 is really Bus 7, Bus 3 = 6, Bus 4 = 5, Bus 5 = 4, Bus 6 = 3,
Bus 7 = 2 and Bus 8 = 1.