H
AL
ALPHA 10/10P SERVICE MANUAL
3
Figure 3
Micro Block Diagram
through the amplifier due to C72 and 74 d.c. blocking capacitors and on average the signal will be symmetrical. Any
short-term asymmetry will be ironed out by the long time constant of the integrator.
Main Power Supply
The main power supply is regulated in two stages. First it is pre-regulated by Q1 and 4 to about 11V less than the
main supply rails. This supply is made available to an option board. The maximum load on these supplies is 150mA
for less than 2W dissipation in Q1 and 4. These supplies are then regulated to +/-15V by Z1 and 2. These supplies are
used by the input stages of the power amplifiers including any 3
rd
channel board, the pre-amplifier board and an
optional phono amplifier board. The positive voltage regulator, Z1, has a larger heatsink than Z2 because the phono
board consumes much more current from the positive rail than from the negative rail.
Control Micro
The control micro performs the following functions...
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Switches the amplifier on or off,
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Mutes the speakers #1 or #2 or the pre-amp output,
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Monitors the heatsink temperature,
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Monitors RF content of speaker outputs,
‚
Handles the remote bus and infra red remote input,
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Reports fault conditions to the main display and LED,
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Reads the speaker and power switch positions.
The control micro runs of the constant power supply from standby transformer, TX2. This enables the amplifier to be
switched on or off remotely from the remote bus or, in the case of the integrated amplifier, from an infra red remote
control. This power supply is intended to supply all the digital circuitry in the amplifier including any option boards.
This is supplied at 8V to the other boards where it will be locally regulated to 5V as required.
The micro communicates with the display board via a multi-master I
2
C bus. This bus is used to report amplifier and
power status to the display micro and remote control commands received. It is also possible for the display micro to
control functions on the power amplifier board. The option board also uses this bus to receive any remote control
commands and communicate with the display micro.
The external remote bus handles raw information from infra red sensors with no demodulating. The remote bus input
can be echoed to the output through a buffer circuit. The incoming signal is demodulated by Z13. Raw signal is also
sent to the micro interrupt line, pin 12, for assessing the noise on the remote bus. In addition, any d.c. signal on the
remote bus is sensed on pin 2 of the micro in when it is not being used as an output to mute the hardware remote
echo buffer. The micro must modulate any output it sends to this bus with a carrier (37KHz). The output will drive one
or two series infra red LEDs directly.
The list below shows how various fault conditions can be deduced simply from the Power LED behaviour.
