Service manual

8 Channel Line Input Board (SPN815-120)
CARD DESCRIPTION
Only one board in a module pair controls and reads the front panel board via a ten way IDC
cable connected to J2. This cable carries switch voltage information and serial data used to
load the LED's on the front panel board.
Issue 1 and 2 boards had digitally controlled attenuators to set headroom gain which were
controlled by serial data and clock from pins 11 through to 16 of U8. Issue 3 boards onward
have push on links to set the headroom gain.
Early modules had a gain control IC (U28) on each input controlled by serial data and clock
from the processor. Issue 3 onwards has a headroom set by a push on link on each channel.
Link Headroom settings are detailed on the board and can be selected from 26dB (0dB
gain), 24dB (2dB gain), 20dB (6dB gain), 18dB (8dB gain) and 15dB (11dB gain).
A trim of approximately +/-0.5dB on each channel is available to match an external peak
signal of +26dBu to 0dBFS in the ADC.
0dBFS Adjustments are as follows. The channel number for the left hand board is first.
Left board Right Board Preset
1 2 VR8
4 3 VR7
5 6 VR6
7 8 VR5
9 10 VR4
11 12 VR3
14 13 VR2
15 16 VR1
An option is available to replace the 24dB setting with a 22dB headroom setting. This board
is part number SPN815A120 and is shipped in module AM4662/22DB. The modification
involves replacing R184 to R191 inclusive with 12k7.
Digital Service Manual
Issue 3 Page 32