Sony PCS-1500 Service Manual page 142

4-1. Check Items Before Starting Self-diagnostics
Symptom: Cannot communicate through the T.120 port.
SS-14
UD-1
Symptom: External microphone cannot be used.
SS-15
PCS-A300 is used
as the external
microphone
External microphone
works when it is replaced
by a normal external
microphone
External microphone is defective
4-12
NO
It cannot be used
YES
NO
YES
CN600 [1-3]
and CN600 [4-5] are
in range of 2.3 V
to 3.5 V ?
AD-00
NO
YES Q601 and its peripheral
PCS-1500/1500P