Check The Usb Ic - NEC MultiSync 20WGX2 Series Service Manual

11.4 Check the USB IC

Is 3.3V supplied to I319 Vcc pin
3,7,11,15,19,23,27,33,39,45,55?
Does X302 oscillate
(24 MHz) ?
Does it have the output of the High Level
(more than 4.75V) from I318, I320
Pin 5 and 8?
Failure point
I318, I320 failure
OK
OK
OK
Proceed "9. Check the DC/DC
NG
converter circuit" section.
Does the output of
X302 satisfy a threshold
NG
level ( High:more than
2.2V,Low:less than
0.8V) ?
OK
Failure point
I308 failure
NG Does I318, I320 short ?
OK
Failure point
Faulty operation of the over
current protection function.
6 - 16
Failure point
NG
X302 failure
Failure point
NG
I318, I320
failure