Acer AM501 Service Manual page 42

8.2.3 No Vertical Deflection ( Raster Become A Horizontal Line)
No vertical
deflection
Check U602 Pin 3
about 12 VDC
Yes
Check U401 Pin 12, 13
output saw-tooth
waveform
Yes
Check U601,R603
Yes
Check D.Y.
Check
No No
R602
No
Check U401
38
Check
power supply
circuit