Tuttnauer 3850 ELVG-D, Technician Manual, Page: 40 / 67

39
10 DETAILED DESCRIPTION OF ELECTRONIC SUB-ASSEMBLIES
10.1 PREDG board
1. U1 Micro-controller (MOTOROLA) comprises of the memory
(RAM and EPROM) A/D which is the central processing unit.
2. U2 Real time clock, contains the date and time of the day with a
100 years calendar, is the pilot clock of the system. It contains the
back up memory for that data which must not be lost in case of a
power failure.
The battery is good for ten years. It is recommended to replace U2
every 8 years.
3. The LCD display, is an alphanumeric display, with 16 characters on
one line.
4. JP2, connector to the printer unit (SEIKO)..
5. JP1 connector to AJUNC3 BOARD.
6. U3, U4, integrated circuit 74H C373 having the function of latch -
drivers for the light signal LEDS, U7 and the valves controls.
7. U5, integrated circuits, has the function of buffer to the dip-switch.
8. U6, integrated circuit has the function of buffer to the keypad.
9. Transistors Q2 and Q7 are the control of the EXHAUST and
WATER valves, as well as of the FAN.
10. Temperature circuit is based on LM34AH, and the component U2.
11. There are also other components like capacitors, diodes and
resistors belonging to the battery back - up and crystal oscillator
circuits.
See electrical schematic drawing for a more detailed view of the board.