Troubleshooting Hints - Sony D98 chassis Operation Manual

8. Vertical Deflection (D/N Boards) Circuit
Theory of Operation
The Vertical Deflection block takes its input from the N-board via pins 13 (VSAWN) and 15 (DCC2). These two signals are
generated by the DSP (IC1002) and are both centered on 1.5V. VSAWN is a sawtooth waveform that controls VSIZE. DCC2
is a DC reference that is compared to VSAWN at IC401. VCENTER is controlled by the shift of VSAWN relative to DCC2.
VSAWN and DCC2 are filtered heavily on the N-board by R1035, R1036, C1009 and C1010 and therefore require the use of
IC1007 as a buffer. Along with a buffer a retrace switch is also necessary to short R1036 and remove the filtering during the
retrace. The retrace switch is internal to the DSP and is found between pins 63 and 64 (see schematic on the following page).
IC401 serves as a transconductance amplifier (it amplifies a low level voltage into a high level current) for VSAWN and the
DC difference between VSAWN and DCC2. The current generated by IC401 is fed to the Vertical Deflection Coil. At the
return point of the Vertical Deflection Coil the current flows through R405 and R403 which generates a voltage across them
which is fed back to the amplifier via R404.
The Vertical Deflection Coil has a large inductance (3mH) and therefore it is very difficult to make large quick changes in the
current without high voltage. This situation occurs during the retrace time (+/-15V is not enough). A circuit internal to IC401
is used to raise the voltage at its output. This circuit works as a charge pump that generates about 40V at pin 6 during retrace
and this is added to +/-15V to generate a total of 55Vpk-pk at the output of IC401. Two external components are used for the
flyback generator. C403 is used as part of the charge pump, while D401 is used to block the high voltage of the flyback pulse
during retrace.
VFB Signal Generation
For D98 VFB is a DC signal. It is generated by rectifying the flyback pulse generated at pin 3. D405 and C409 do the
rectification while R417 and R418 the DC level appropriately. If the flyback generation at IC401 does not work (ie. IC401
malfunctions) then the DC level at this point will be reduced and trigger the Vertical Shutdown Protection Mode after one
second the set's LED will blink amber for 1.5 sec. and then off for 0.5 sec. This is the indication of a scan failure.

Troubleshooting Hints

Vertical Scan Failure
The first step is to check the shutdown log of the monitor and make sure the microprocessor has detected a loss of VFB.
Once this has been verified the output of IC401 should be checked. If a normal output exists after the remote on/off bit is
turned on but the monitor still shuts down then the VFB detection circuit (see VFB signal generation section) is malfunc-
tioning. If no output exists signal tracing should begin at IC1002 pin 1 for VSAWN and pin 2 for DCC2. In shutdown
mode both of these levels should be 1.5V DC. If the remote on/off bit is turned on a sawtooth waveform of about 1Vpk-pk
should appear on VSAWN while DCC2 stays at 1.5V this should last about 2 seconds until a loss of VFB is detected and
the monitor shuts down again. If these signals are good check for the same signals at the output of the N-Board pins 13
(VSAWN) and 15 (DCC2) by repeating the remote on/off step. If no signal is present the problem is with IC1007, if
present continue tracing to R410 and R406. If the signals make it this far the problem is likely in the IC401 area.
IC401
4 5 6 7 1 2 3
D401
R407
C403
D405
R417
C409
R416
- -
20
V.FBP
R418