Samsung SG626, SG628, BG626, BG678, SG676 Circuit Descriptions

6. Circuit Descriptions

1. Power circuit

WHT GRY

GRNREDBLK

L V T

CON1

BLK

BLU

(DC12V)

C107
470uF

25V

V12

(DC12V)

C109

104

+12

Vcc

(DC5V)

BD05-08

1N4004 X 4

1

FUSE2

250V 0.5A

1

3

3
5

5

7

1N4004 X 4

C103

BD01-04

7

HEAT-STICK

+

C

C106

1000uF

35V

7812

(MC7805)

IC02

HEAT-STICK

7812

(MC7812)

HEAT-STICK

7805

(MC7805AC)

+

IC03

ICO1 +

IC03

C

470uF

25V

104

+

Circuit used

+12

Voltage

(DC 12V)

Vcc (DC 5V)

V12 (DC 12V)

Relay Operation

Power around MICOM & Sensor Detector

LED Display & S/W Detector

The input AC voltage of DC-trans secondary registers 15V at CON1 between ①~③. The rectified
voltage passed through BD05 ~ 08 becomes DC 12V through volt age regulator MC7812(IC02). The
power(DC12V) is supplied to the relay operation power block. Then, DC 5V is genetatel and supplied
to the power around micom and sensor detector through 7805(I C03).
The rectified voltage passed through BD01~04 passes through 7812(IC01). Then, DC12V is supplied to
LED display and switch detector.

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2. Oscillator

30P

30P

Port

Oscillating Fr equency

Xin

Xout

±0.5% Error

3. Reset Circuit

R201

1K

KA7533

C203

1µF/25V

Port

x-tal

30

31

4.00MHz

4.00MHz

R202

29

10K

C202

104

Voltage

Xin

Xout

RESET

It is designed for clock generation and time
calculation for synchronizing transmission and
reception on the logic elements inside the MICOM.
If the X-TAL specification changes, MICOM may
make an error. The standard components should be
used.

When power is supplied to MICOM, reset circuit
initializes RAM and other parts on MICOM to
initialize all programs. Reset voltage maintains
“low” for hundreds of µsec comparing to MICOM
Vcc voltage when power is input. It also maintains
“high”(5V) during normal operation. But, when Vcc
drops to 3.3V, reset port becomes “low”.

Xin

Xout

4. Door S/W Detector

F-DOOR S/W

R-DOOR S/W

5V

5V

CON06

Vcc

R401(4.7K)

R403(4.7K)

R402

10K

R404

10K

C401

104

C402

104

7

8

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DOOR

F

Door Conditions

CLOSE

OPEN

Door S/W Contact

OPEN

CLOSE

MICOM

PIN NO

# 7

Micom Input Voltage

“LOW”

“HIGH”

CLOSE

R

OPEN

OPEN

CLOSE

“LOW”

# 8

“HIGH”

1) If door is open, door S/W contact is closed. Then MICOM receives “low” signal and detects
door open.

2) If door is closed, door S/W contact is open. Then MICOM receives “high” signal and detects
door close.

5. “V” Motor Position Detector(Reed S/W)

CON 02

REED S/W

7

6

5

Vcc

R405

4.7K

R406

10K

C403

104

43

1) The position of “V” motor for controlling the G.A–fuzzy of the temperature in the
refrigeration room is detected by the reed switch.

2) When MICOM Pin 43 changes ‘high’ to ‘low’ by the operation of fan, MICOM detects the
position of “V” motor.

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6. Temperature Sensor

R2-ROOM

R1-ROOM

THERMISTOR

F-ROOM

THERMISTOR

R / DEF - SONSOR

THERMISTOR

F / DEF - SONSOR

4
3
2
1

1
2
3
4
565

CON2

4
3
2
1

CON3

1
2
3
4

6

Vcc

Vcc

Vcc

Vcc

Vcc

"A"

R301

10K-F

R303

10K (F)

R305

10K (F)

R307

10K (F)

R309

10K (F)

Vcc

( Air Sensor)

R311

10K (F)

R302
10K
R304
10K

R306
10K
R308
10K
R310
10K

R312
10K

104

C09
104

104

104

104

104

C301

C302

C303

C304

C305

C306

60

P64

59

P63

62

P66

61

P65

58

P62

63

P67

When Sensor is open

MICOM input “HIGH”

When sensor is cut off

MICOM input “LOW”

1) The sensor uses the characteristics of thermistor. If temperature goes higher, resistance goes
lower. On the contrary, if temperature goes lower, resistance goes higher.

2) MICOM input voltage is counted by sensor as follows.

VF = X Vcc

RTH

RTH + R24

(VCC : 5V, RTH : Sensor reisitance)

3) For the resistance information on temperature and MICOM input voltage, please refer the
conversion table. (Page. 41)

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7. Key scan and display circuitry

IC04

R502

1.2K

3

4

5

6

7
8
9

GND VCC

UDN2003(2803)

IC05

1
2
3
4
5

13
10

16

15

14

13

12
10

C23
104

18
17
16
15
14
6

9

C501
3K

P04

P03

P02

P01

P00

P75
P74
P73
P72
P71
P70

13

12

11

10

9

6
5
4
3
2
1

R503
1K

1) Key scan and display operation

+12

GRID 05
GRID 04
GRID 03
GRID 02
GRID 01

R501
3K

R04

4. 7 K

CON7

(XH-11P)

10

11

10

10

9

9

9

4

4

4

3

3

3

2

2

2

Quick
REF

HIGH

Alarm

HUMI

X-Flow Quick FRE

Quick

Quick REF

FRE

1N4148

1N4148

1N4148

1N4148

1N4148

S/W01
S/W02
S/W03
S/W04
S/W05

X1 X2 X3

1

1

1

5

5

5

6

6

6

7

7

7

8

8

8

11

11

KEY INPUT

X4 X5 X6

F Temp. R Temp.

C C-N N N-W W

C C-N N N-W W

As shown in the following waveform, MICOM pins #2 ~ #6 output are high for 2msec per 10msec.
MICOM pin #2 → #3 → #4 → #5 → #6 output repeats. The signal is output through IC05(UDN
2981A). At that time, the peak to peak voltage of square signal registers around 11V. The grid #1 ~#5
waveforms are as follows.

2 m Sec 8 m Sec

V

11V

Grid #1

Grid #2

Grid #3

Grid #4

Grid #5

O
V

O
V

O
V

O
V

O

Refrigerator Display

t

Freezer Display

t

Letter Display

t

“V” Function Display

t

“V” Function Display

t

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2) Key Scan

The grid waveform of each output is supplied to each button line through switching diode
(IN4148). The grid #1 signal goes to the setting button of refrigerator. Then, refrigerator button
is pressed, around 4.5V goes to IC05(UAN2981A) pin 8 through key input line. MICOMdetects
the refrigerator button pressed after MICOM pin1 receives the signal.

8. Load Operation

RY09

RY01

RY02

RY03

RY04

RY05

RY06

RY07

RY08

+12

+12

(DC12V)

C27
104

IC06

18 1

11 8

12 7

13 6

15 4

15 3

17 2

18 1

Vcc GND
ULN2803

IC07

17 2

IC06

(R-DEF-HET)

14

(R-LAMP)

(F-LAMP)

(COMP)

P05

16

P07

18

P11

19

P12

P14

21

22

P15

23

P16

24

P17

17

P10

P06

R03

C24

10K

104

(COMP-COOL FAN)

R
C

SWING MOTOR

I
N
E

(R CIRCLE-FAN)

T
W
O
R
K

(F CIRCLE-FAN)

9

AC1

C25

R02
10K

104

(F-DEF-HET) 15

R-Defrost heater

COMP COOL FAN

SWING MOTOR

R-C/FAN

R-LAMP

F-LAMP

F-C/FAN

COMP.

F-Defrost heater

CON9
RED

CON10

CON8

9

9

7

7

5

5

3

3

1

1

9

9

7

7

5

5

3

3

SPK1-4
SQ-1201

1

1

5

5

3

3

1

1

V12

If MICOM outputs “high” signal to driver-IC(ULN 2803) according to each load operation
conditions, IC turns on and DC 12V flows to ground through the relevant relay coil. Then, core is
magnetized by the coil current, and relay contact switches on. When relay contact is on, AC POWER
is supplied to the relevant operation load, then which will be activated. If MICOM outputs “low”
signal, load operation stops with the relevant relay contact off.

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1) Compressor and Defrost Heater

RY08

AC POWER

NC NO

COMP

F-Defrost heater

R-Defrost heater

CC

NC NO

RY09

RY01

As above block diagram, the commons of compressor relay(RY 08) and defrost heater relay(RY 09,
RY 01) are respectively connected to AC POWER line. If relay is not activated(OFF) contact
maintaills NC, and compressor and defrost heater are all off, activated and contact is switched on.
Then, AC POWER is supplied to compressor activated. On the contrary, if defrost heater relay
operates, defrost heater is activated. Compressor and defrost heater do not operate simultaneously
under any conditions of relay.

RELAY

COMP

on

Defrost H

off

Load

Comp Operation

Defrost-Heater Power Off

Remark

on

off

off

on

on

off

Comp off, Defrost-Heater Off

Defrost-Heater On

Comp Off, Defrost-Heater Off

Comp Power Off

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9. Other option functions

Vcc

49

P50

50

P51
P52
P53
P54

P30
P31
P32
P33
P34
P35
P36
P37

51
52
53

33
34
35
36
37
38
39
40

R33 - 40
47K X 8

R12-16 1K X 5

51 41 31 21 11
52 42 32 22 12
53 43 33 23 13
54 44 34 24 14
55 45 35 25 15
56 46 36 26 16
57 47 37 27 17
58 48 38 28 18

10. PCB Sub Ass’y(Inverter PCB)

Temperature and function values are changeable by using
main PCB switching diode.

• Note : If possible, do not change be cause the values have

been set in factory. When changing option functions,
power should be turned off.
(Only initial power-on allows reading option
function)

TH-SW

C4
D8

D10

R9

R8

R3

R2

F1

C1

LF1

RT1

D1 D2

D3

D4

+

C3

R1

Q4

C8

C2

R10

PT2

D5

DAC

R4

PT3

ZD1

Q1

R5

CH2PT-1

CH1

Q2

R7

Q3

R6

D11

RT2

C6C5

D9

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1) Power circuit

PCB sub ass’y (Inverter PCB) is activated with AC POWER input when the refrigerator door is open
and R-lamp relay(RY05) is activated. If the AC POWER is supplied to the power block, the smooth
capacitor(C3) gets around VOLTAGE DC(VOLTAGE AC X 2) AC POWER through rectification.

2) Lamp

If power is supplied to the PCB sub ass’y, diac(DB4) is activated. When C4 is over 35C/DC, voltage
is supplied to TR Q2 base by the continuity of diac. Then, TR Q2 is activated.
When TR Q2 is activated, current flows to C5 – C6 – CH1 – PT1 – R9. At that time, current flows to
PT2 and PT3.
If the discharge of capacitor C6 is completed, reverse current flows to PT2 and PT3 and TR Q2 turns
off TR Q3 turns on. The current flows to PT1 – CH1 – C6 – C5 – C8.
Lamp light up by the repetition of TR Q2, Q3 on/off. Its frequency range is 30~40KHz during
on/off.

3) PTC and PTC protector

PTC is designed to smooth the lighting and to lengthen lamp’s life by heating filament of lamp. The
PTC protector prevents damage from PTC by cutting off power through triac if filament emits high
voltage at the beginning of lighting.
To check the PTC, measure resistance (150Ω ± 25% is normal). But, PTC resistance can be challged by
the ambient temperature and PTC operation. The above resistance value is counted in 20 sec after
lamp is off with the temperature 25˚C.

26 Samsung Electronics

4) Troubleshooting

Precautions

1. Is the power cord well connected to wall outlet?

2. Be careful of high-voltage discharge because high voltage DC power is supplied to SUB-PCB.

① When the light dosen’t come on in the refrigerator

Start

Is power supplied to

sub-PCB?

Y

N

Is power supplied to

smoother C2?

N

Is TH-S/W normal?

Y

Does lamp oscillate

Y

Check the power

at 35±5KHz?

N

Check PTC.
Replace lamp

Replace TH-S/W

✻ PTC should be inspected before replacing lamp.
✻ Be careful of high voltage discharge, when repairing unit.

N

Check wires and
main PCB relay

Y

Repair C6, C7 or
PTC(RT1)

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