Philips PM32671 Service Manual page 38

2-22
Z-LOGIC
This stage sends a current signal t o the Z amplifier to control the intensity of the spot on the c.r.t. screen. The
spot intensity depends on the mode selected; e.g. MTB, MTB intensified by DTB, DTB, A L T TB, EXT X DEFL,
and also on the position of the INTENS control R12.
During the hold-off period the display must be blanked. The current that determines the intensity is
tion of the collector currents of transistors V288 and V289. Both transistors are controlled by the logic circuits:
V288 by NAND-gate output D218-12 and V289 by NAND-gate output D218-6.
I f both logic outputs are L, V288 and V289 conduct and the display is unblanked. The logic levels on 0218-12
and D218-6 as a function of the mode selected are given in Fig. 2.6.
OUTPUT D218112
X D E F L = L
Fig. 2.6 Important voltage waveforms in the Z-modulation control logic
MTB only
During the MTB sweep, input D217-2 is
during the sweep.
Input D217-5 i s
H
during this time, and also D218-1.
NAND-gate input D218-2 is permamently
comparison).
input D217-12 is H during the MTB sweep, so OR-gate output D217-11 i s
Input D217-9 i s
Input D218-3 i s H. Output D218-6 is
DTB only
Input D217-4 is
Input D217-1 is
Input D218-2 i s permanently H, so output D218-12 is
Input D217-10 i s
during the DTB sweep.
Input D206-2 i s L, so output D206-3 and also input D217-13 go t o logic H. Consequently, the OR-gate output
Input D218-3 is permanently a t
OUTPUT D218/6
M T B
ONLY
H,
H
if the MTB output signal is routed t o the final X amplifier. As a result, OR-gate output
H.
As a result for gate output D217-8 is
L during the MTB sweep (compare with Fig. 2.6/1).
H
during the DTB sweep, which makes output D217-6 and input D218-2 logic H.
H
and consequently output D217-3 is
H
during the DTB sweep, which makes output D217-8 and also input D218-4 a t logic H
H
so output
X DEFL= L
MAT913
resulting in OR-gate output D217-3 and D218-13 becoming H
H L
so output
and also D218-4.
H
and also input D218-13.
L during the DTB sweep (compare this with Fig. 2.6/3).
D218-6 i s L during the DTB sweep (compare this with Fig. 2.6/3).
during the MTB sweep
(see
H
and also D218-5.
summa-
a
Fig. 2.6/1 for