Sony D98 chassis Operation Manual page 8

6. Troubleshooting
Warning
Before attempting to fix the power supply, safety should be consider first. Never connect test probes to the primary side
circuits, unless proper isolation has been installed. If isolation for the AC mains is not present, serious harm can occur.
Never assume you are safe.
No Power
In the event that the monitor does not turn on, first check F601 and R615. If these parts are blown, the primary side circuitry
should be checked. If the fuses are not blown, then check the secondary side circuitry, especially the protection circuits. If
these circuits are causing a no power symptom, the problem can be more readily found.
AC Input and Degauss Circuit Trouble Shooting
For no power or nonoperating power supply, the AC input circuitry should be checked. Open or short circuit elements will
cause non-operation. F601, CN600, CN603 and CN2003 On the H Board should be checked first. The wiring between the
AC switch on the H Board and D Board should be checked. Check the front panel AC switch for continuity.
If all elements are correct, check whether F601 breaks when power is applied and the AC switch is closed. If the fuse does
blow, there may be problems with the primary circuitry or a component short.
The degauss will malfunction if CN601 is not connected. One problem could be loss of degauss signal from N Board. This
can be verified by using the manual degauss command found in the OSD menu. If the signal does not appear at R670, then
check the signal on the N Board and all connections. It is possible that the microprocessor does not function correctly.
The second step is to place a short across the AC terminals of RY601 for less than two seconds. If degauss operates then
check Q670 and RY601. If degauss does not work, check THP602 for an open condition and VA601 for a short condition.
Primary Section
Three main areas can diagnose primary circuit failures. These are IC601, Q602 and Feedback system.
Visible checks of these areas will aid in finding problems. The following will discuss each section.
IC601
First apply AC to the monitor and check IC601 pin 6 output. If the output on pin 6 is not present or briefly appears, there
could be problems with Q602 and related parts. Further, check VCC level at pin 7. If it less than 9 volts, the IC could be
in latch mode. If the voltage is very low, there could be a short on any of the IC pins. In reference to ground check the
impedance of pin 1, 6, 7 and 9. If any of these pins are shorted, replace the IC and check components connected to the
related pins. Pin 1 is especially vulnerable to damage. Take care that C619 and C616 are fully discharged before replacing
the IC.
Q602
The switching transistor can be damaged in various ways. These are related to voltage, current and temperature.
Check whether the transistor is shorted across drain and source terminals. If there is a short, R609, R615 and FS601 should
be checked. R609 is usually broken when Q602 fails. Additional components to check are D603, D604 and IC601. If
Q602 is shorted, all these parts should be replaced.
Failure of a secondary rectifier diode can also cause Q602 to fail. Check B+ and 80V diodes for open or short conditions.
There is also a clamp circuit, which is used to clip the turn off spike found on Q602 drain. If the clamp circuit is broken, it
can cause Q602 failures. Check D615, C622 and R619.
Secondary Circuit
Failure in the secondary circuits can be categorized by rectifier diodes, fusible resistors, regulators, +5 volt back up circuit,
feedback loops and protection circuits. These sections are interrelated and failure in one can affect another. Consequently,
some failures will also affect the primary circuitry.
Rectifier Section
Rectifier diode failures are not common, but do occur. Deflection, video and N Board failures contribute to diode damage.
In the event a voltage is not present, check for shorts to ground, open or short diodes. Also check fusible resistors or any
zener diodes found on the voltage lines.
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