Sony STR-DE845 Training Manual page 23

5. Analog Signal Block
The signal from the analog switching ICs (IC301and IC303) passes through Buffer IC304 (located on the Main
board), and then splits off in two directions after CNP11. One path is to IC1502 (Output Select IC), which is used
when the receiver is set to 2CH mode. Note: The digital board is totally bypassed when 2CH mode is selected.
The other connection is to the Digital board through CNP7 pin 1. The signal at this point can be viewed on either
side of C1522 (6Vpp). The signal then goes through R1522 (10kohm), which causes significant signal loss and
the signal is too low to probe at IC1504/pin 6. The signal is amplified by IC1504 and the signal levels at the
output are 1.4Vpp (pin 7) and 1.4Vpp (pin 1). The signals at pins 7 and 1 are identical, but 180 degrees out of
phase. The signal is then applied to the IC1503 (ref. Appendix for CODEC functional description) to be A/D
converted. The digital output signal at pin 9 (IC1503) is difficult to view on an analog oscilloscope. Waveforms
5-1 and 5-2 illustrate what can be viewed on an analog oscilloscope. Note: When attempting to view Waveforms
5-1 and 5-2, use the HOLDOFF control on the oscilloscope to lock the digital packets on the display as shown.
The display will only lock on the packets when an audio signal is applied; otherwise, the display will be unsteady
as shown below.
Oscilloscope Settings:
5V/div
10us/div
Trigger trailing edge
Adjust Holdoff
WAVEFORM 5-1 WAVEFORM 5-2
DISPLAY LOCKED ON PACKETS DISPLAY UNLOCKED ON PACKETS
NOTE: There is no output signal at IC1503/pin 9 when in either 2CH or Analog mode (MODE button selection).
The audio outputs of IC304 are also connected directly to IC1502 (Output Select IC). IC1502 selects inputs on
pin 19 and pin 10 and sends it to the outputs as a 2-Channel format.
All the waveforms from IC1301/pins 22 (SOA), 23 (SOB) and 24 (SOC) to IC1503/pins 6 (SDI 1), 7 (SDI 2) and
8 (SDI 3) are identical throughout the path (IC1301, IC1403, IC1401 and IC1503). Once again, in the digital
domain these waveforms are difficult to lock on the display of an analog oscilloscope. Waveforms 5-3, 5-4 and
5-5 show what should be displayed when probing the three signal paths (SOA, SOB and SOC) in normal operation.
Use the HOLDOFF control to lock the data packets on the display. If there is not an analog input, the packets will
not lock (unlocked waveform illustrated by Waveform 5-2). The main concerns while viewing these waveforms
are: 1) there is no loss of data input (IC1301/pin 85) causing unlocked display condition; and 2) there is data
present on all lines (no open traces).
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