The Service Manual received was helpful. The electronic information is exactly what I needed.
Text excerpt from page 24 (click to view)
EN 24
5.3.4
5.
DVD728-731 /0X1
Service Hints, Trouble Shooting and Fault Finding
No Sound
B When read disc, Laser ON OK? Signal LDO1 and LDO2  is normal? Y Y Voltage of TP22 &TP24 OK? N Check the peripheral circuit of two transistor (item 7620 & 7621) Check the peripheral circuit of MT1366 Check the peripheral circuit of two transistor (item 7620 & 7621)
N
N
Load a disc?
N
Laser off Y
Check the circuit to connect LOADER OPU maybe damaged
Y
Focus On ok?
N
Any signal on pins A B C D E F of MT1366 Y Signal FEO (pin18 of MT1336) correct?
N
Check the circuit between Loader and MT1336
N
Check the peripheral circuit of MT1336
Y
Y Check the circuit from Pin18 of MT1336 to Pin205 of MT1379
Disc ID correct?
N
Signal of Pin 19 (RFL) of MT1336 normal? Y Check the circuit from Pin19 of MT1336 to Pin206 of MT1379
N
Check the peripheral circuit of MT1336 and itself.
Y
Spindle on OK?
N
DMSO (pin18 of MT1379) normal? Y Signal SP+  &  SPcorrect?
N
Check MT1379 and its peripheral circuit.
N
Check BA5945 (motor driver) and its peripheral circuit
C
Y Check the connection between spindle driver and BA5945
