Pioneer CX-3195 Manual de servicio - Página 4

Navegue en línea o descargue pdf Manual de servicio para Receptor para automóvil Pioneer CX-3195. Pioneer CX-3195 27 páginas. Cd mechanism module

1.1 PREAMPLIFIER BLOCK

In the preamplifier block, the pickup output signals are processed to generate signals that are used in the subsequent

blocks: servo, demodulator, and control blocks. Signals from the pickup are I/V converted in the pickup with the

preamplifier with built-in photo detectors, and after added with the RF amplifier, they are used to produce such signals as

RF, FE, TE, and TE zero-cross signals. The preamplifier block is built in CD LSI PE5547A (IC201), whose parts are

described individually below. Incidentally, as this LSI employs a single power supply (+ 3.3 V) specification, the reference

voltages of this LSI and the pickup are the REFO (1.65 V) for both. The REFO is an output obtained from REFOUT in the

LSI via the buffer amplifier, and is output from the pin 133 of this LSI. All measurements will be performed with this REFO

as the reference.

Caution: Be careful not to short-circuit the REFO and GND when measuring.

1.1.1 APC (Automatic Power Control) circuit

Since laser diodes have extremely negative temperature characteristics in optical output when driven in constant current,

it is necessary to control the current with the monitor diodes in order to keep the output constant. This is the feature of the

APC circuit. The LD current is obtained by measuring the voltage between LD1 and V3R3, and divide the value by 7.5

(ohms), which becomes about 30 mA. The voltage between LD1 and V3R3 is set to about 225 mV.

Pickup Unit

LD-

LD+

Fig.1.1.1 APC

CD CORE UNIT

143

REG 1.25V

142

PE5547A

CX-3195

6.5k

Vref

APN

100k

150k

LDS

100k