Philips DVDR890 Service Manual page 46

9.2.4 EEPROM
The EEPROM M24C16 [7808] is an electrical erasable and
programmable, non-volatile memory. The EEPROM stores
data specific to the device, such as the AFC-reference value of
the Europe IF-part, the clock-correction-factor, etc. It is
accessed by the µ P via the I
9.2.5 Sync Separator
TTo detect whether a video signal is available or not a sepa-
rate IC [7825] is used to extract the sync information out of the
video signal that is also routed to the digital board for record-
ing.
While on the input a low-pass-filter ([2823] and [3869]) limits
the bandwidth an additional filter (circuit
around [7818]) on the output avoids distortions. Afterwards the
sync-signal is routed to pin11 of the CC.
9.2.6 Fan Control
To avoid unwanted temperatures inside the set (especially the
Laser on the OPU of the drive is very sensitive) a fan is
located on top of the basic engine. The speed control is
dependent on the ambient temp. A NTC resistor [3172]
located on the display board measures the temperature. An
operational amplifier [7902-B] generates a proper voltage,
which is then fed to the engine ("BE_FAN"-line). Below 28°C
ambient temp. the fan-voltage is approx. 5V and is increased
to 10V when the ambient temperature goes up to approx.
35°C. The second part of the Op-Amp. [7902-A] prevents dam-
age of any temperature-sensitive part in case the NTC or the
wire in between is damaged. It acts as a comparator and pulls
the "BE_FAN"-signal to 10V. As the fan has to be stopped in
case the tray of the drive is open this voltage is "killed" by the
CC ("FAN_OFF"-signal). The double-diode [6903] acts for both
Op.-Amp.-circuits.
9.2.7 Power Supply
The 5SW and 8SW supply are switched off in case of standby
from the P via the ISTBY-line. This is possible for power-save.
The ISTBY-line must be low in case of STBY. There is also a
„power fail" circuit on the PS-schematic which is necessary to
mute AUDIO when IPFAIL is low.
9.3 Analog Board Europe
9.3.1 General
This PCB consists out of the following parts:
• Power-Supply-Unit
• Frontend (Audio & Video)
• Input/Output-switching
• Audio ADC- & DAC-processing
• VPS/PDC- and Text-Data slicer
• Analog Follow-Me Circuit
All functional groups are either controlled via I
separate signal lines by the Central-Controller on the µ P-Sub-
Board. This sub board is directly soldered in onto the analog
PCB. During Stand-By mode of the set, several parts are not
supplied (Tuner, MSP, ...). The microprocessor is running and
maintains the clock of the set.
To avoid bus blockades the I
from these units is decoupled via transistors [7419], [7420]
from the general bus ("SCL" & "SDA").
Circuit-, IC Descriptions and List of Abbreviations
2
C-bus.
2
C-bus or via
2
C-bus ("SCLSW" & "SDASW") to/
DVDR880-890 /0X1 9. EN 149