Philips 20PT643F Service Manual page 54

Set turns on, but with a half screen at the bottom. Sound is okay. Blinking
o
LED (set is in SDAM mode) indicates error 3. Check 'Vlotaux+11V' and
'+50V'. If they are okay, problem is expected in the vertical amplifier IC
7471. Use an oscilloscope to measure the waveform on pin 17 of the
UOC. Also, measure the waveform at pin 1 of IC 7471. If the signal there
is missing, a defective resistor R3244 caused the problem.