FL 8370 (serv.man4) - Harman Kardon Audio Service Manual (repair manual). Page 11

FL8370

1.1 RF Amplifier

The optical currents inputted through pins PD1(A+C) and PD2(B+D) are converted into voltages through
I-V amp, and they are added to RF summing amp. The voltage, converted from the photo diode
(A+B+C+D) signal, is outputted through RFO(pin74) and the eye pattern can be checked at this pin.

Figure 4. RF amp circuit

1.2 Focus Error Amp

The output of the focus error amp is the difference between I-V amp(1) output VA and 
RF I-V amp(2) output VB. The focus error bias voltage applied to the (+) of focus error amp can be
changed by output voltage of D/A converter as shown in diagram, so that the offset of focus error amp
can be adjusted automatically by controlling 5 bits counter switches. Focus error bias can be adjusted
from the range of +100mV ~ -100mV by connecting the resistor on pin 63 (FEBIAS).

Figure 5. Focus error amp circuit

note1> VA and VB refer to output signal of PD1 and PD2 I/V amp.
note2> sev-stopb,sev-stop,fe-stopb and fcmpo are internal signals

65

66

-

-

74

-

73

PD1

PD2

RFO

RF-

58K

10K

VA

I-V amp(1)

VC

58K

10K

VB

I-V amp(2)

VC

VC

RF summing amp

63

-

59

-

-

sev-stopb

FEBIAS

sev-stop

32K

32K

<5 Bit Counter>

3K

X1

X2

X4

X8

X16

164K

FE1

160K

4K

fcmpo

vc

FEBIAS

fe-stopb

SW1

VB >

VA >

fe-stopb

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