Philips DVDR615 Service Manual page 130

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EN 130 9.
9. Circuit-, IC descriptions and list of abbreviations
9.1 MOBO (Analog) Board
9.1.1 General
The pcba consists of the following parts:
• Control unit Slave µP
• Power supply unit
• Frontend (Audio & Video)
• Input/Output switching
• Audio ADC & DAC processing
• IR Blaster (for EPG sets only)
9.1.2 Control unit Slave µP
The core element of the MOBO analog board is the slave µP
TMP87CM74AF [7107].
It runs on a 5V supply and is responsible for the following
functions:
• Interface with the Chrysalis chip on the FEBE Digital
backend
• Evaluation of the keyboard matrix on the Front board
• Decoding the remote control commands from the infra-red
receiver
• Activation and control of the display
• Heater voltage generation
• Fan control
• IR Blaster (for EPG sets only)
It runs on a high clock frequency of 8MHz with resonator [1101]
and a low clock frequency of 32.768kHz with resonator [1102].
9.1.3 Interface to the Chrysalis chip
The communication to the Chrysalis chip on the FEBE Digital
2
backend is done via I C interface, where the TMP87CM74AF
acts in slave-mode.
9.1.4 Evaluation of the keyboard matrix
A resistor network on the Keyboard (on the Front board) is used
to generate a specific direct voltage value (KEY1- & KEY2-
line), depending on the pressed key. Via the resistors [3152]
and [3154] on the analog/digital (A/D) ports, [7107] pin 32 and
32 the evaluation is done.
9.1.5 IR receiver and signal evaluation
The IR receiver [7200] on the Keyboard (on the Front board)
contains a selectively controlled amplifier as well as a photo-
diode. The photo-diode changes the received infra red
transmission to electrical pulses, which are then amplified and
demodulated. On the output of the IR receiver [7200], a pulse
sequence with TTL-level, which corresponds to the envelope
curve of the received IF remote control command, can be
measured. This pulse sequence is fed into the controller for
further processing via pin 22 [7107].
9.1.6 Vacuum Fluorescence Display
The VFD BJ900GNK [1100] is fully controlled by the
microcontroller. The microcontroller also includes the driving
stages. Only two additional drivers [7109] and [7111] are
necessary for the grids 8 and 9 because of their large size.
9.1.7 VFD Heater Voltage Generator
The circuit around [7102], [7103] and [7104] is used to
generate a proper AC-voltage for the filament of the VFD. For
this the microcontroller generates an appropriate rectangular
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DVDR615/69 Circuit-, IC descriptions and list of abbreviations
signal with 50% duty-cycle and a frequency of 30kHz at pin 19.
[5101] and [2111] are acting as resonance circuit. Via zener-
diode [6102] and resistors [3111], [3113] and [3114] the two
heater pins of the VFD (FIL1 and FIL2) are clamped so that the
grids and segments can be fully switched off.
9.1.8 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
at the rear of the FEBE module. The speed control is
dependent on the ambient temperature. A NTC resistor [3211]
located on the Keyboard (on the Front board) measures the
temperature. The change in temperature is translated into dc
levels and send to pin 28 of slave µP [7107]. High / low signals
is then sends out via pin 5 and 6 of slave µP [7107] to control
transistors [7105] and [7106] which regulates the fan motor to
3 different speeds
9.1.9 Power Supply Unit
Functional principle:
This power supply works in the way of a flyback converter. In
the mains input part [1931 to 2314/2315], the mains voltage is
rectified and buffered in the capacitor [2314/2315]. From this
direct voltage at [2314/2315] energy is transferred into the
transformer [5300, pins 7-5] during the conductive phase of the
switching transistor [7308] and is stored there as magnetic
energy. This energy is passed to the secondary outputs of the
power supply in the blocking phase of the switching transistor
[7308]. With the switch-on time of the switching transistor
[7308], the energy transferred in every cycle is regulated in
such a way that the output voltages remain constant regardless
of changes in the load or mains voltage. The power transistor
is driven by the integrated circuit [7311].
Mains input part:
The mains input part extends from the mains socket [1931] to
the capacitor [2314/2315]. The diodes [6302, 6303, 6305 and
6307] rectify the AC supply voltage, which is then buffered by
the capacitor [2314/2315]. The common mode coil [5303] and
capacitor [2310] work as a filter to block interference arising in
the power supply from the mains. Components [1302], [3316]
protect the power supply against short-term over voltages in
the mains, e.g. caused by indirect lightning.
Start-up with Mains-on:
After connecting the power cord to the mains, the capacitor
[2332] is loaded via a current source between pin 8 and pin 1
in the IC [7311]. Once the voltage on [2332] and therefore the
supply voltage V of the IC [7311] has reached approx. 11V,
CC
the IC starts up and provides pulses at its output pin 5. These
pulses are used to drive the gate of the power transistor [7308].
The frequency of these pulses is depending on load and mains
voltage. The current consumption of the IC is approx. 5 mA at
V in normal mode.
CC
If V drops to below approx. 9V (e.g. with power limitation) or
CC
if V exceeds approximately 16V (e.g. interruption of the
CC
control loop), the output of the IC [7311, pin 5] is blocked and a
new start-up cycle begins.
(See also Overload, Power Limitation and Burst Mode section)
Normal operation:
With the power supply in normal mode, the periodic sequences
in the circuit are divided primarily into the conductive and
blocking phase of the switching transistor [7308]. During the
conductive phase of the switching transistor [7308], current
flows from the rectified mains voltage at capacitor [2314/2315]
through the primary coil of the transformer [5300, pins 7-5], the
transistor [7308] and resistors [3330, 3331] to ground. The