AOC P/N : 41A50-144 - Manual (Page 19)

18
KEYBOARD BLOCK check
OK
Check U302 pin 38 (LED green) will have
transition from hi to low or low to hi when we
press the power key??
Press power key and check U302 pin 43
= low (0V) ?
OK
Replace Tact-switch SW105 at keyboard if still
no work replace U302 MCU at main-board and
check MCU relative reset circuit, and crystal
OK
Check U302 MCU pin 43,42,41,40,39 at
High state(5V)? without press any key Mechanical was stuck, Check !
NG
NG
If still no Led green indicator, check Q102,
R106 & LED at keyboard !! cold solder or bad
NG, MCU no response
Check U302 pin 20= 20MHz ? and pin 44
(VDD)=5V ? and pin 10 (reset)=0V ? at normal
condition
If one of this item was NG, check the relative
circuit
NG
Without press key and change mode, Check U302
pin 16,17(sda,scl)= hi 5V ? or keep transition ?
OK
Check U300 eeprom 24LC04 relative circuit,
check U300 pin 7 = low?
Keep transition, that means eeprom no response
Check JP202 is
connect ?
NG
NG
Check U300 pin 8
(vdd)= 5V, and check
R300,R301 cold solder
OK
Replace eeprom
Replace U302 MCU
OK, no keep transition