Sony D98 chassis Operation Manual page 15

Rotation Coil(CN702)
4. Rotation/Vertical Key Circuitry Mounted on the D/N Boards) Circuit
Theory of Operation
The Rotation/Vertical Key circuitry takes its input from the N-board via pins 40 (Rotation) and 42 (D.Tilt). D. (Dynamic)
TILT is generated by the DSP (IC1002) while Rotation is generated by the microprocessor (IC1001). Rotation is a PWM
waveform at approximately 40kHZ measuring 5V pk-pk at pin #3 of the microprocessor. While D.TILT is a triangular
waveform at the vertical scan rate, 1.0Vpk-pk in amplitude centered at 1.5V. Typical waveform patterns are provided as
figures #1 and #2 below. Rotation is filtered by the R729 and C705 combination and a DC offset is added to D.TILT from the
+5V line via R735. These two waveforms are added together and amplified by IC702. This amplifier is a transconductance
amplifier (it amplifies a low-level voltage into a high level current). The output current from pin 4 of IC702 flows through
R709 and the rotation coil and returns to ground through R708. The feedback is sensed at R708 and sent back to the amplifier
through R707. The DC level of the current through R708 is controlled by the Rotation signal while the triangular currant
amplitude is controlled by the D.TILT waveform.
FIGURE 1
T1 21.60us
T2 150ns
DT 21.75us
Vertical Key Circuit Troubleshooting Hints
It is possible to have a malfunction of only the Vertical Key portion of the circuit. This can occur by a loss of signal from
D.TILT. First check if the Rotation function is working properly. There should be no more them a +/-15 degree picture
rotation by operating the rotation function through min-max extremes. When the Rotation function is at its full position (SV
at R729) the voltage at R708 should be a positive 2.25 vdc, approximately. And at its full negative position this voltage
should be a negative (-) 2.5 vdc approximately (NOTE: if D.TILT is open or shorted to ground these voltages will not be well
centered around 0V).
Rotation/Vertical Key Circuit
+16V
IC702
5
R709
R775
4 V+ +
V-
C701
3
R707
R708
-16V
C702
0
+5V
R735
R736
42
IC1002(DSP)
R737
0
0
1 R729
40
-
2 ROTATION
C705
N-BOARD
0
FIGURE 2
T1 1.10ms
T2 2.60ms
DT 13.70ms
- -
15
D.TILT
59
3
IC1001