Power Supply On I/O Board - LG RH178H Service Manual

2. POWER SUPPLY ON I/O BOARD

No 12V
YES
NO
Is the VCC (14V) sup-
plied to Q164 Collector?
YES
NO
Is there about 12.5V at
ZD151 & Q164 Base?
YES
NO
Is the VCC (33V) sup-
plied to Q162 Emitor?
YES
NO
Is there about 0V
at Q162 Base?
YES
NO
Is there about 5V at R171
and 0.7V at Q156 Base?
YES
Check Q156 and
Replace
No 5.2V
YES
NO
Is the VCC (5.3V) sup-
plied to Q151 Emitor?
YES
NO
Is there about 0V at D153
and Q156 Collector?
YES
NO
Is there about 5V at R171
and 0.7V at Q156 Base?
YES
Check Q156 and
Replace
Check D124 on SMPS
Board and Replace
Check Q164 and
Replace
Check D126 on SMPS
Board and Replace
Check Q162 and
Replace
Check the 'PWR CTL
H' signal from µ-COM
Check 5.3VA on
SMPS Board
Check Q151 and
Replace
Check the 'PWR CTL
H' signal from µ-COM
No 5VT
YES
Is the VCC (5.3V) sup-
plied to Q155 Emitor?
YES
Is there about 0V at D152
and Q152 Collector?
YES
Is there about 5V at R180
and 0.7V at Q152 Base?
YES
Check Q152 and
Replace
No 33VT
YES
Is the VCC (33V) sup-
plied to Q161 Emitor?
YES
Is there about 0V
at Q152 Collector?
YES
Is there about 5V at R180
and 0.7V at Q152 Base?
Check Q152 and
Replace
3-4
NO
Check 5.3VA on
SMPS Board
NO
Check Q155 and
Replace
NO
Check the 'TIMER H'
signal from µ-COM
NO
Check D126 on SMPS
Board and Replace
NO
Check Q161 and
Replace
NO
Check the 'TIMER H'
signal from µ-COM