Product specifications

DA100 (50Hz) and DA50W Chassis – Repair Notes
Page 38 of 80
Vertical Stage
Circuit Operation
The operation of the vertical output circuit is similar to the audio with the exception that there is no mute
circuit, although C511 will stop the circuit from operating until the +13V supply, is present.
Figure 35: Vertical Output Amplifier
The PWM signal from pin 4 of the IC, is passed through a low pass filter (L352 and C504) producing a ramp signal
at the field deflection coils. This ramp waveform will vary between +13V when the scan is at the top of the
screen decreasing to –13V when the scan has reached the bottom of the screen. The field scan coils are returned
to ground via Q503. Q503 is turned on during the vertical scan period and turns off during vertical fly-back.
IC502 will produce an error signal. This error signal is fed to the vertical drive input (IC501 pin 11), for the
purpose of linearity and amplitude correction.
Vertical Fly-Back
At the point where vertical fly-back is initiated Q503 turns off and Q502 turns on, allowing the +25V supply to
connect to the field scan coils. Since there is –13V on the other side of the scan coils derived from the vertical
drive signal, we effectively have 38V across the field coils, which will force the scan to the top of the screen.
The vertical drive signal that is comes from IC801, pin 31, has a negative going pulse in addition to the normal
ramp waveform. This negative pulse is used to initiate vertical fly-back. This drive signal is applied to the emitter
of Q505 via R508. The potential divider R526 and R514 will fix Q505 base voltage so that it will only turn on
during the period of the negative going pulse. Once Q505 turns on its collector voltage will fall turning on Q507
taking its emitter to ground, which results in:
Sharp Electronics (UK) Limited - May 2003
Revision 3