No Power Troubleshooting; Feedback Circuit Troubleshooting - Sony CPD-420GS Training Manual

No Power Troubleshooting

(IC601 Troubleshooting)
First apply AC to the monitor and check IC601/6 output. If the output at
pin 6 is not present or briefly appears there could be problems with Q602
and related components. Check VCC at IC601/7. If the voltage is less
than +9V DC, IC601 could be in the latch mode. If the voltage is very low,
R613, R623, D605, D624 and D657 should also be checked respectively.
If no problems can be identified, in reference to Hot ground, check the
impedance of each pin at IC601. If any of these pins are shorted, replace
IC601 and check components connected to the related pins. Take care
that C616 and C619 are fully discharged before replacing IC601.
IC601/6 PWM
23
(Q602 Troubleshooting)
Q602 can be damaged in various ways such as voltage, current and tem-
perature. Check Q602 for shorts. Further checks to F601, R609 and
R615. Additional components to check are D603, D604 and IC601. There
is also a clamp circuit, which is used to clip the turn off spike found on
Q602 (D). Check D615, C624 and R619.

Feedback Circuit Troubleshooting

Problems with the feedback circuits can cause power supply shut down
or low voltages. First determine whether the power supply is operating in
'Active Off', 'Active On' modes or not at all.
The power supply can be stuck in 'Active Off' mode. The Remote ON/
OFF signal from the N Board, Q656, Q658, IC603 and IC652 can affect
this condition. In addition, check the protection circuits.
Q602/Drain