Troubleshooting Short Circuit Protection - Sony CPD-420GS Training Manual

Secondary Short Circuit Protection
Short Circuit Protection for the secondary low voltage supplies are de-
tected in different ways.
1. The "B+ DET" line is used to detect the loss of the -16V DC supply
through circuit elements R611 and R612. R611 is connected to the
+5V DC from IC605 and R612 is connected to the -16V DC supply
from T601. The node voltage between R611 and R612 is monitored
by the Micro IC1001/14 (N Board). If the node voltage exceeds +2V
DC, IC1001/6 goes H (+5V) turning Q657 ON, shunting normal regu-
lation feedback. This causes IC601 to increase the drive output to the
point of OVP latch via pin 7(VCC).
Note: LED illuminates Orange (0.5 seconds) / Off (0.5 seconds)
27
2. The +16V, +12V and +5V DC secondary voltages are monitored
through circuit elements D641, Q640 and R641. The +80V DC from
T601 through R641 is applied to Q640 (C). Normally the +5V DC
from IC605 and D641 turns Q640 ON and Q657 OFF. If there is a
substantial short circuit on any of the secondary low voltage supplies,
the +5V DC standby supply can be attenuated. If it goes lower than
+3V DC, Q640 will turn OFF. With Q640 OFF, Q657 turns ON to
bypass the feedback voltage from IC603. This causes IC601 to in-
crease the drive output to the point of OVP latch via pin 7.

Troubleshooting Short Circuit Protection

The power supply can be operated in the "Active Off' mode to better trouble-
shoot each circuit under reduced voltages by simply disabling the 'RE-
MOTE ON/OFF' line from the N Board by lifting pin 16 of CN801. Q640
and Q657 should be check respectively.