M2 MC2125PALS Service Manual - page 44

45

Circuit Descriptions

9-9) Option Circuit 

9-10) Load Drive Circuit

9-8) EEPROM Circuit

EEPROM is semiconductor memory not to be

erased. It can be used in the area of unstable

electric power.

1) The control of load in the system is accomplished by the main PCB.

2) Most of relays or SSRs can control the compressor, refrigerator/freezer defrost heater, and several option functions.

3) For the compressor, #18 pin of micro processor signals High (5V). This signal enters #5 pin of IC3 and #14 of output

terminal which have base and collector functions of IC3 turns on and connects the GND. Relay 73 will be grounded

through #14 of IC. Magnetic field will generate so that the second side of RY73 is activated and 115V is supplied to

the compressor. On the other hands, if #18 of micro processor turns Low(0V), #5 of IC3, the current of RY 73 relay,

and magnetic field will shut down in sequence. A contact point in secondary side of Relay 73 is off. Finally compressor

will stop.

There are a variety of models that have a

different function. A different model can set up to

use option circuit as shown.