Read Harman Kardon HD 755 (serv.man9) Service Manual online
Focus System
The focus error output of A, B, C and D are given to Pin 27. C4 is required for oscillation-
proof. R7 is set such that FEOUT of Pin 27 becomes 1.46 Vp-p.
During alignment procedure, the DSP IC (MN662790) will adjust the focus balance voltage
V
FBAL
from Pin 30. V
FBAL
varies with reference to the center voltage V
REF2
(=1.65 V) within
±
0.5 V.
The focus gain will change according to the type of disc. For normal disc or CDR disc,
V
GCTRL
is set to V
REF2
; for CDRW disc V
GCTRL
is set to V
REF2
- 0.75 V. At the same time, the
tracking gain is changed too.
A
B
C
D
F
PDIC
E
36
34
28
29
27
26
GCTRL
FBAL
Subtraction
R7
FEN
C4
FEOUT
V
GCTRL
C2
C3
R6
V
FBAL
35
33
3
5
C35
C47
R27
R21
R20
12
HD755
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