AOC Vibrant VL7A9DA Service Manual page 19

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