Service manual

8 Channel Line Output Board (SAI800-036)
CARD DESCRIPTION
Only one board in a module pair controls and reads the front panel board via a ten way IDC
cable connected to J3. This cable carries switch voltage information and serial data used to
load the LEDs on the front panel board.
Issue 1 and 2 Line Output boards had digitally controlled attenuators to set headroom gain
which were controlled by serial data and clock from the processor.
Issue 3 boards and above have push on links to set the headroom gain. The headroom link
positions are marked on the circuit board. There is however an error on Issue 3 boards. The
26dB headroom position does not work without the fitting of 8 off 15k resistors in positions
R355 to R362. With these resistors in place the other headroom settings are wrong so they
should only be fitted for 26dB headroom working. This error is corrected on Issue 4 boards.
Issue 4 boards have an adjustment for the reference supply to the DACs. This will help to
allow for output level change with power supply voltage. VR1 should be set to give 4.75V
+/-0.05Von the positive end of C289. This adjustment can be adjusted finely to control the
average output level of the 8 channels on the board.
An option is available to replace the 24dB setting with a 22dB headroom setting. This board
is part number SAI800A036 and is shipped in module AM4663/22DB. The modification
involves replacing R347 to R354 inclusive with 7k5.
Digital Service Manual
Issue 3 Page 31