A SMPS supply, built around U2 and TR1, is used to provide the supplies for the amplifier circuits
(+/- 18 V).
These +/- 18 V signals are regulated to several other DC voltages by linear voltage regulators:
+ 18VDC TP1
+ 15VDC TP11
+ 12VDC TP2
- 5VDC TP4
- 15VDC TP72
- 18VDC TP3
- 22 VDC TP73 (non stabilized for LCD contrast)
The +18 V and –18 V are used as supply for the amplifier circuits. Therefore they are constantly
monitored by U45. In case of a strong deviation, the voltage lockout (UVLO) signal becomes
‘LOW’, the safety relay will be switched off and an error will be generated.
The UVLO signal is connected to the safety processor.
Since the +18V is used in the feedback loop for the SMPS, the –18V may fluctuate. In order to keep
this voltage within the limits, there is a clamp system (built around Q14) installed onto this supply.
VCC (+5 VDC) is also generated by a SMPS built around U30.
The VCC is also constantly monitored (U46). If this voltage goes below 4.75 V, there will be a reset
signal (POR) and the safety system will be activated.
The POR signal is directly connected to the microcontroller.
5.1.2 Micro-controller Circuits.
The 16 bit micro controller (U3: Siemens C167) is the heart of the system that controls and drives all
the other circuits and signals, together with the safety controller (U36: PIC 16C74)
The program software is stored in a flash memory (U54, U55: AM 29F800). An upgrade of this
software can only be done by means of a PC, which must be connected to the unit in order to
download the software (chapter x).
The actual version of the software is displayed in the start-up screen.
The micro-controller uses external RAM (U42 and U41: 256K each).
A separate display controller (U49: SED 1353) + RAM (U39 and U40: 256 K each) perform the
controls of the LCD display.
U50 is a programmable peripheral interface IC which drives mainly the relay circuit.
Other components near the microcontroller circuits are:
Temperature sensor RT1
: measuring the temperature of the heatsink, which controls the working of
the fan in the following way:
- Temperature > 55°C: switch on fan
- Temperature < 45°C: switch off fan
- Temperature > 98°C: error and switch off all amplifier circuits.
Phyaction Guidance E/C – service manual version 0.5 Page 15
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