Electrical Troubleshooting Guide; Power(Smps) Circuit - NAD T 751 Service Manual

ELECTRICAL TROUBLESHOOTING GUIDE

1. Power(SMPS) Circuit

A.
No FLD
Is 5.2VA section working?
YES
Are D109, L103 open?
YES
Replace SMPS trans(T101).
Replace the inferior
components.
NO
NO
No 5.2VA.
Check R127, 128.
(SHUTDOWN CKT)
Is 5.2V applied to IC102
Pin 1?
NO
Is there a DC voltage at the
(+) terminal of BD101?
YES
Is R102(R104) normal?
YES
Is about AC 100V app;ied to
IC101 Pin 3.
NO
Check IC101.
3-2
B.
No 5V_D
or 5V_A .
Is 5.2VA section working?
NO
(Is the POWER CTL at
Pin6 High/low?)
YES
NO
Is oscillation present at the
Base of Q108?
YES
Replace Q108.
YES
Check D109, C123, R125,
R124.
NO
Replace BD101.
(Bridge rectifier)
NO
Replace R102.