NEC FP1355 Service Manual page 38

Examples of the functions and current waveform/compensation operation of YH(YHTT,
YHTB, YHJT, YHJB) are shown as follows.
In the above formulas, b11T, b11B, b12T and b12B express the compensation coefficients,
and y and y^2 express the primary and secondary functions of the vertical frequencies.
The other parts except the compensation coefficients are programmed, and desired ampli-
tudes (= compensation amount) are gained by varying the coefficients.
YHTT and YHTB compensate the upper and lower parts of the picture of the characteristic
components of their DYs to compensate the upper and lower parts of the picture of the
axis deviation component. The component gained by adding YHT and YHJ is multiplied by
the offset compensation coefficient a11. The resultant component is regarded as 4H_SC,
and is output from IC601 (CP267P151=uPD61882BGC) pin 61.
(2) Waveform, and operation on the picture
The case in which the currents flow through 4H coils of the sub yoke is explained. Re-
garding YHT (secondary function in the vertical frequency), in case of Fig 17 as an ex-
ample, the current is large in the same direction at the start (upper end of the picture) and
the end (lower end of the picture) of the vertical frequency, and is zeroed on the X axis of
the picture. Therefore, the magnetic field that is proportional to it is generated, and RED
and BLUE vary in the same direction only at the upper and lower ends of the picture. As
aforementioned, YHT can be independently controlled at the upper part (b11T.y^2) and
lower part (b11B.y^2).
Moreover, regarding YHJ (Primary function in the vertical frequency), if the flowing direc-
tion of the current is opposite at the start (upper end of the picture) and the end (lower end
of the picture) of the vertical frequency as an example, RED and BLUE vary in the oppo-
site direction only at the upper and lower ends of the picture. Compensation in the vertical
direction can be done by making the current flow to the 4V coil.
Fig.19(a) and (b) shows the image of each adjustment item of the DDCC adjustment.
(3) Adjustment method
Before the adjustment with the compensation circuit, it is necessary that they are properly
adjusted at the center (H-STATIC and V-STATIC), on the X axis (XH slider, B-Bow 4P, XV
differential coil) and on the Y axis (YH volume, YV volume).
Though DC current is superimposed on the sub yoke, H-STATIC and V-STATIC are
pushed to the greatest possible extent by the adjustment with CP ring in order to reduce
the stress of the driver IC8A1 (STK391-110).
Moreover, since 4H and 4V coils alone are installed on the chassis, it is first necessary
that the convergence of RED, BLUE and GREEN (6H, 6V) satisfy the specifications for the
performance of ITC(CRT&DY).
As the adjustment procedure, the adjustment values of 30 elements are not respectively
zeroed but they are adjusted to nearest to zero with a total balance in good order.
In other words, the balance (compromise) adjustment with each adjustment item is applied.
The correspondence of the names of DDCC adjustment mode to the coefficients of all 30
elements is shown below.
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