Philips 28PW9618, Service Manual

Page: 148 / 172

Circuit Descriptions, Abbreviation List, and IC Data Sheets
EN 148 EM6E 9.
Muting: The "mute" of the receiver is controlled by the IF
receiver part, but can be overridden by the microcontroller.
The "mute" action initiated by the microcontroller is necessary
during channel switching and in the standby mode. Muting has
priority on all other main tasks. The hardware mute is the result
of an "AND" function between the “Tuned” and “Stereo”
information. The "tuned" information can be read by the
microcontroller on pin 2. The same pin has to be put in output
mode to activate the microcontroller initiated "mute". This
"mute" must be used during the frequency setting and during
the standby mode.
Power save mode: The main supply can be switched off with
the “power save” control line to reduce the current
consumption. The microcontroller is always powered by the
power supply. All other electronics can be put into power save
mode.
After approx. 10 minutes of no "Tuned" signal the receiver goes
into power save mode. Once in power save mode, the receiver
is operated in “listen-sleep” mode to reduce the average
current consumption.
Power Supply
The board is having a low drop voltage regulator 7790, which
has an output voltage of 8 Vdc.
The 5 Vdc supply for the micro controller is extracted from the
10 Vdc input supply via a zenerdiode 6751. The 5 Vdc supply
of the synthesizer is extracted from transistor 7606. The
POWERSAVE signal is also provided to the connector for the
amplifier.
Amplifier (Diagram W)
General
The amplifier module delivers 2 x 15 Watt into 4 ohm speakers.
There is an incorporated high-pass filter because of the use of
soft-flat panels as speaker. The speakers are connected
through 2.5 mm mono-jacks. The crossover will be around 150
Hz. The amplifier uses a “cool power” amplifier IC
(TDA1564TH).
The module is featured with an additional “wired backup” input
(3.5mm stereo-jack) and a 2-colour LED indicator. Green
indicates the active state, red is standby. There is also an on-
board 10 Vdc regulator, specially intended for the TX receiver.
DC-references and Supply
The reference voltage used in the preamp-filter is made of the
internal reference of the amplifier chip TDA1564TH. This
reference is buffered by 7100-D and present on pin 14 of 7100-
D. The reference is only valid when the chip is active or muted.
The power supply for the pre-amp is made by using the filter
circuitry 3100, 2101, and 2100. This supply is 10.6 Vdc for all
operating conditions.
The built-in voltage regulator LM317MDT delivers 10 Vdc for
the receiver board. The 10 Vdc is set by 3141 and 3142. This
is the normal operating condition by wireless use of the whole
set.
This 10 Vdc supply can be switched "off" by connecting a 3.5
mm plug into the "wired backup" input. By doing so, the base of
7103 is connected to ground, 7111 is saturated, and pin 1 of
7110 is on ground level. The result is 1.25 Vdc on the supply
line to the receiver.
Mute Circuitry
In normal operating circumstances, the voltage on the MODE
pin of the amplifier will be 9.7 Vdc. Transistors 7104 and 7107
are not saturated at that moment. When the receiver generates
a ”mute” (4 Vdc on pin 6 of connector 1106), then 7107 will
saturate and pulls down the level on pin 2-7101 to 2.3 Vdc. All
DC-references stay as they were, the LED stays green, but no
sound is produced on the outputs.
When the receiver goes into "power save" mode (when 10
minutes no signal from the TV set), the circuitry around 7104
pulls the mute line down to nearly 0 V. In this condition, the
amplifier is completely in "standby" mode, while all DC-
references are disabled. The LED red will be "on", while green
is "off".
When the receiver detects a valid signal from the TV set, the
POWERSAVE line becomes continuously "low", and after a
small time (2137, 3133, 7104) 7104 is turned "off". At the same
moment, the mute line becomes "low" and the amplifier is
enabled again.
Amplifier considerations
The 26 dB amplifier TDA1564TH operates on 13 Vdc and can
deliver 2 x 15 Watts into 4 ohm loads. The dissipation is
minimized by internally switching in the TDA1564 from Single
Ended (SE) to Bridge Tied Load (BTL) mode, only when a
higher output voltage swing is needed.
Input signals from the receiver (or the 3.5 mm stereo jack) input
are filtered in the two-section high pass filter around 7100-B
and 7100-A. This is needed because the flat panel speakers
cannot reproduce low frequency sound. The -3 dB point is
somewhere around 150 Hz.
Input sensitivity of the amplifier for maximum output:
•
Wireless use (signals coming from the receiver board):
typical 1.4 Vrms
•
Wired use (signals coming from the 3.5 mm jack input):
typical 2.5 Vrms
9.9
Software Upgrading
9.9.1
Introduction
In this chassis, you can upgrade the software via ComPair.
This offers the possibility, to replace the entire SW image
without having to remove the flash-RAM from its socket. You
can find more information on how this procedure works in the
ComPair file. It is possible that not all sets are equipped with
the hardware, needed to make software upgrading possible. To
speed up the programming process, the firmware of the
ComPair interface can be upgraded. See Chapter Service
Modes, Error Codes and Faultfinding paragraph "ComPair" -
“How To Order” for the order number.
9.9.2
Specifications
Some specifications are:
•
The upgrade feature makes use of I2C to transfer a new
SW image (4 MB).
•
It requires the ComPair interface Box (RS232 to I2C).
•
The I2C bus is available at the rear side of the set, BUT it
is still necessary to open the set to place a dedicated
jumper. This, to avoid FCR (Field Call Rates).
•
It uses a ZIP-compressed BIN software image to speed up
the transfer process (1/2 size).
•
The complete procedure takes less than 20 minutes with
an upgraded ComPair interface:
–
About 90 seconds to erase a 4 MB flash-RAM.
–
Less than 10 minutes to transfer the file (max 1.9 MB).
–
About 5 minutes to decompress/program the flash-
RAM
Note: It takes about 85 minutes with a standard interface.
Constraints:
•
Needs the EPG flash memory, so this device must be
placed also for non-EPG regions like AP and US.
•
The new SW image must ALWAYS contain the bootstrap
code (see below).
Advantages:
•
Flexibility.
•
No change in IROM required (IROM not used).
•
Flexibility to change of code flash manufacturer as the
"flash driver" is part of the bootstrap code (part of the main
software image).