Bose FreeSpace 4400 Service Manual page 79

If anything other than a shutdown command causes the amplifier to go into protect mode (i.e.
AC dropout, over-voltage / under-voltage, short circuit, DC or high frequency), the speakers are
immediately disconnected, and the amplifier is shut down for approximately 3.5 seconds. It is
then restarted and checked again after a 1 second stabilization period. If everything is not OK, 6
more off-wait-stabilize-reset cycles are attempted, normal operation can resume after any of
these. If after 6 retries within 1 minute, everything is still not OK, the amplifier is returned to a
state that requires a "Standby-On" cycle, a "hard power down" or some other form of user
intervention to restart.
Measurement
Measurement of the rail voltages and numerous other parameters are accomplished via an
internal 10-bit A/D converter section in PIC uC U14. Most inputs to the A/D are multiplexed
(under the PIC's control) via 8-channel analog switch U15. The A/D's output is truncated to 8
bits and incorporated into the I2C datasteam going to the host processor on the DSP PCB.
Heatsink temperature is monitored via U12, which provides a calibrated output of 10mV/
Several gain, precision rectifier, average circuits are provided to condition the following signals
for measurement via the MPX - A/D section (via voltage across R91):
• Amplifier input voltage
• Amplifier output voltage
• Amplifier output current
To provide repeatable, reliable measurements, the time constant of all these averages is ap-
proximately 100 mSec.
Bose ® FreeSpace ® Installer™ software uses these measurements to calculate answers to
questions , such as; "Is the amplifier set up and running properly, and providing adequate output
voltage?"
Fault Logging
The amplifier PIC microprocessors are in continuous communication with the 4400 amplifier's
host processor via the I2C serial link. Pin 26 of the PIC micro is connected high or low on the
two amplifier PCBs so the host can distinguish between the upper or lower amplifier PCB. If any
of the events mentioned in the protection section cause the amplifier to shut down, an "Amplifier
Status Record": plus a set of amplifier measurements (Vout, Iout, TEMP, Vrail, etc.) is saved into
flash memory. Some of the more common fault conditions can be identified by a careful exami-
nation of these status records.
Amplifier Operating States
Pins 4, 5 and 6 on the PIC microprocessor programming headers (JP1 lower) or (JP2 upper)
provide a binary indication of which one of 6 states of operation the amplifier is in. If you monitor
these pins, you can observe the states being walked though, and determine where operation is
getting interrupted.
THEORY OF OPERATION
79
o F.