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WARNING: Disconnect primary power prior to servicing.
Overall System Theory
4.7.5.2 PA Power Supply Discharge
When the PS_DISABLE signal goes high, all of the SCR taps are disabled and the
DISCHARGE signals at J1-7 and J2-7 go low. This activates the PA Power Supply
Discharge circuits on the rectifier boards, which allows a quick and safe discharge
of the PA supply.
4.7.5.3 Power Supply Standby Mode
Under certain circumstances, such as RF Mute, the power supplies will be placed in
standby mode via the signal PS_STANDBY. This signal comes from the Master
Controller and both PA Controllers. PS_STANDBY shuts off all the DRIVER
signals which deactivates all of the SCR taps on both power supplies. However, it
does not activate the discharge circuit. This allows the filter capacitors to maintain
charge and be ready to supply power at a moments notice without having to go
through the Soft-Start sequence again. However, the capacitors will bleed down
slowly if the standby mode is maintained. To keep the voltage within reasonable
limits, the PS Controller will activate the Soft-Start circuit if the PA voltage drops
below 42Vdc and shuts it off when the voltage is above 52Vdc. The PS Controller
will maintain charge in this manner until the PS_STANDBY signal goes low, and
the power supplies are fully active again or shut off by the PS_DISABLE signal.
4.7.5.4 Discharge Protection Circuit
The discharge protection circuit protects the power supply and the discharge circuit
components from a failure in the discharge circuit. Specifically it protects against a
short which would cause the discharge resistor to be “In circuit” when the power
supply is activated.
A sample of the voltage across the discharge resistor from each supply is sent to the
PS Controller at J1-20 and J2-20. If the voltage is more than 30Vdc, the comparator
will trip, and the output at U1-1 or U1-2 will go LOW. The fault signal
1_DISCH_SAMPLE or 2_DISCH_SAMPLE is then sent to U9-2 or U10-2 where it
is buffered before reaching the micro-controller. The PS Controller would then shut
down the power supply. The detection circuit contains a lot of hysterisis to prevent
false triggering.
4.7.5.5 RESET
There is a RESET line from the Life Support Board which is monitoring the
+20Vdc from the regulators on the Rectifier Boards. This is basically monitoring
the Low Voltage Power Supply. If the voltage falls below a set threshold, U37 on the
Life Support Board generates the RESET (active low) which is sent to all of the
controller boards (Master, PAC and PSC). On the PS Controller this RESET clears
U2 and U3, which brings their outputs low. This deactivates all of the DRIVER
signals, disconnecting all of the SCR taps and shutting off the supply. This also
activates the DISCHARGE(BAR) signal which then bleeds off the supply.
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