Samsung DSB-S300G Service Manual page 25

Troubleshooting
SPDIF Output Missing (Optical)
Check +5V
at Pin2 of J702
Yes
Check ΠDigital Audio
signal at R714
Yes
Check J702 Optical Jack
Failure mode
5-6
No
Check +5V Drive
No
Check Failure mode
U302(STi5100)
ΠDigital Audio signal at
R714
Samsung Electronics