Sony D98 chassis Operation Manual page 9

Horizontal Centering
Loss of horizontal center adjustment can be affected by the rectifier diodes, fusible resistors, IC502 and related circuitry.
Measure the voltages in reference to the horizontal centering ground. Typically, the voltages are ±8 volts. However, the
adjustment setting can reduce the voltages by 1 volt. If there are no problems found with the diodes or fusible resistors, the
next step is to check the adjustment signal at Q517. If the adjustment signal is not present check the N Board and connec-
tions. Otherwise, check IC502 and related components.
+5/12 Volt Regulator
Loss of voltage due to shorts or device failures on either +5 or +12 volt output lines can occur. Consequently, IC605 can
be damaged and need replacing. Before replacing IC605 check for shorts or damaged parts along the output lines. If +12
volt does not appear, check the remote on/off signal. The N Board supplies this signal and it may be necessary to check it
and all connections.
+5 Volt Standby Circuit
Failure of this circuit can be affected by IC605. The remote on/off signal controls circuit operation and it may need
checking. In case the circuit does not work properly, check D619, R617 and Q601. If these components are good, check
the remaining circuit parts.
Heater Voltage Regulator
This circuit may be affected directly by fusible resistor R654 or D654. If these parts are good, check the regulator output
for a short to ground. Shorts can occur on the video board. In the case of an output short, IC604 may have been damaged.
If the IC appears to have no damage, check the connections and N Board for any problems with the heater on/off signal.
Feedback Circuit
Problems with feed back 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, Q656 and IC603 can affect this condition.
Likewise, if the power supply is always in active on mode, the same items should be checked.
Checking for voltages at IC603 pins 1 and 2, IC652 pins 2 and 3 can solve more difficult problems. Additionally, IC603 pin
4 and IC601 pin 9 should be checked. If there are problems with these devices, B+ or 16.5 volt line, the feedback systems
will not work correctly. Also check the protection circuits.
Protection Circuits
OCP occurs when there is excessive current through Q602. Failures with Q504, Q505 or the video section commonly
cause this condition. These areas should be checked. OCP condition can also occur if R609 is open or if there are prob-
lems with IC606 or Q605.
OVP usually occurs when the feedback loop is open, secondary voltage shorts or loss of +5 volts. Isolate the OVP trigger
condition, by first checking the operation of the feedback loop and Q657. Either PWR shutdown or Q640 can turn on
Q657. The feedback loop can be verified by removing Q657 and measuring the B+ voltage level.
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