Dynamic Focus Circuit; Horizontal Dynamic Focus Correction; Vertical Dynamic Focus Circuit - Sony CPD-G400 Training Manual

Dynamic Focus Circuit

The job of the dynamic focus circuit is to change the focus points to match
the flat picture tube screen. This is done in the horizontal plane by in-
creasing the DC focus voltage when the beam at the left and right sides of
the screen. A similar correction is required in the vertical plane when the
beam is at the top and bottom.
Although the dynamic focus correction circuitry is an independent pro-
cess, the same IC801 (DPU) makes the vertical and horizontal dynamic
focus correction signals. The separate VDF and HDF outputs feed indi-
vidual amplifiers before being capacitor-coupled to the static (DC) focus
voltage at the flyback transformer T901.

Horizontal Dynamic Focus Correction

The main input needed by IC801 to construct the horizontal dynamic fo-
cus signal is the flyback pulse (HFBP) at CN1006/pin 15. The vertical
sweep signal (VFBP at CN1005/pin 11) is also needed for additional cor-
rection when the beam is at the corners of the screen. The DPU (IC801)
uses both of these inputs to make a HDF signal that leaves the N board at
CN1005/pin 14.
The HDF signal is amplified and inverted by Q701 – Q705. Transformer
T701 couples the signal to the flyback's static focus voltage for horizontal
focus correction.
Horizontal Dynamic Focus Signals
Name Location DC
HDF CN1005/14 1.81V
Q701/base 1.25V
Amplified Q701/ 23.2V
HDF collector
T701/pin 2 24.2V
Final T701/pin 8 0V
HDF
signal
* All voltages and wave shapes taken in the Aging Mode.
AC Wave Shape
0.8Vp-p
0.8Vp-p
44Vp-p
44Vp-p
500Vp-p
63
Amplifier Stage DC Voltages
Q701
Q702
Q703
Q704
Q705

Vertical Dynamic Focus Circuit

The vertical dynamic focus correction signal is made in DPU IC801 using
vertical and horizontal sweep signals from CN1005/pin 11 and CN1006/
pin 15. The simple parabola shaped VDF correction signal is amplified by
IC503 and driver Q706. The resultant 200V VDF signal is capacitor coupled
to the FC focus voltage inside FBT T901/pin 15.
Vertical Dynamic Focus Signal Path
Location
CN1005/pin 15
Q706/base
Q706/emitter
Q706/collector
All voltages and wave shapes taken in the Aging Mode.
Troubleshooting
When you are only able to focus the monitor at the center of the screen
and not the sides or corners, the dynamic focus stage is not working. In
all operating modes of this monitor, HDF and VDF signals will be output
from IC801. Trace these signals to the FBT T901.
Note: If you disable the HV (short Q902/G-S) for signal tracing, the +300V
and the final VDF signal at Q706/Collector will not be present.
Emitter Base Collector
0.6V 1.25V 23.2V
24.5V 24.8V 77.1V
23.7V 23.1V 0V
24.2V 24.5V 77V
24.0V 23.75V 0V
DC AC Wave
Shape
1.8V 1Vp-p
4V 9Vp-p
3.5V 9Vp-p
145V 200Vp-p