25/08/2004 ©
Söring
Service-Manual Arco- and RF-units
1
not valid for A-3000/ -2000
2
not valid for Arco-2000
-22-
3
not valid for MBC600
4
not valid for Arco-1000
Voltage monitoring:
-+5V-source:
Over voltage protection: This unit is activated if the 5V-source exceeds the limit (+10%).
In case the limit, determined by a zener diode, is exceeded, a thyristor is fired and short-
circuits +5V to the thyristor voltage (1.2V).
In case of permanent short circuit the thyristor is protected against overheating (>85°C)
by the thermal fuse SI3, which is thermally coupled to the thyristor. If the temperature at
the thyristor exceeds 85°C, fuse SI3 melts and interrupts the connection to the
22VAC/50Hz.
Under-voltage protection: If the voltage of the +5V source is less than 4.65 V, the µc-
monitor-IC (MAX691A) sends a reset signal to the CPU.
-
±
15V source:
If the voltages exceed or fall below the limits +15V
±
10% or -15V
±
10%, the unit sends a
reset signal to the CPU. The unit works with voltage comparators and reference voltages
given by zener diodes.
D) Microprocessor-monitoring
An external watchdog WD1 monitors the quartz frequency of the CPU. At intervals of
200ms the CPU sends a trigger signal to WD1. If the interval exceeds 240ms or falls
below 160ms the watchdog transmits a trigger signal to the CPU. Simultaneously the
disconnect switch interrupts the feeding of the power supply. Furthermore the CPU is
halted by a reset, if the above mentioned voltage monitor is activated.
Power supply watchdog: With the power supply watchdog the supply voltage of the high-
power supply (disconnect switch) can only be switched on, if the CPU periodically sends
a trigger pulse in 200ms intervals. A reset signal of the CPU generally switches off the
disconnect switch.
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