AOC LCD Monitor P/N : 41A50-144 Service Manual page 20

POWER-BLOCK check
*
*Note : the Waveform of U304 pin 2 can determined the power situation
1. stable rectangle waveform with equal duty, freq around 150K-158KHz
that means all power of this interface board is in normal operation
,and all status of 5V & 3.3V is working well
2. unstable or uneven rectangle waveform without same duty, that means ABNORMAL operation was
happened, check 3.3V or 5V ,if short-circuit or bad component
3. rectangle waveform with large spike & harmonic pulse on front side , means all 3.3v is no load, U200
Gmzan1 was shut-down, and only U302 MCU still working , that means the monitor is in power saving
status , all power system is working well .
Measure input power at U304 LM2596 pin 1=
12V ?
Check U304 pin 2 is a stable rectangle wave?
Around 150k-158kHz stable rectangle wave
with equal duty without any spike or harmonic
pulse?
The interface board power is good
OK
OK
NG
Check ADAPTER and connector if
NG
Check U304 pin 2 is a unstable rectangle wave ?
OK, unstable wave
Check all 3.3V & 5V power, there is
short circuit or bad component was
happened
19
loose?
The interface board is in power-
saving state, press power key to wake
up & check your signal input
NG, with
harmonic
pulse