Read Sharp 76FW-54H Service Manual online
DA100 (50Hz) Chassis – Article for Television Magazine
Scan Velocity Modulator
The purpose of this circuit is to maintain the luminance level as the electron spot moves across the
CRT face.
The distance that the electron beam travels from the electron gun to the CRT face at the outer edges
of the CRT is greater than the distance from the electron gun to the centre of the CRT face. This
distance is emphasised more on 16:9 CRT’s than 4:3 CRT’s with deflection angles of 110°
This result in the intensity of the electron spot varying as it travels across the CRT face. To overcome
this a coil is placed around the CRT neck, close to the gun assembly. The purpose of this coil is to
increase/decrease the speed, the spot travels across the CRT face, therefore, maintaining luminance
transitions.
CRT face.
The distance that the electron beam travels from the electron gun to the CRT face at the outer edges
of the CRT is greater than the distance from the electron gun to the centre of the CRT face. This
distance is emphasised more on 16:9 CRT’s than 4:3 CRT’s with deflection angles of 110°
This result in the intensity of the electron spot varying as it travels across the CRT face. To overcome
this a coil is placed around the CRT neck, close to the gun assembly. The purpose of this coil is to
increase/decrease the speed, the spot travels across the CRT face, therefore, maintaining luminance
transitions.
Figure 59: Scan Velocity Modulator Circuit
Circuit Description
The signal that is used to control this circuit is derived from IC801 pin 34 and the amount of
correction can be adjusted by the end user via the picture menu. The drive signal is based upon the
luminance signal and controls the conduction of Q5407 and Q5408 depending upon the intensity of the
signal at that point of the scan/screen location. If there is a bright area at the edge of the picture,
the current in the SVM coil will increase and accelerate the electron beam. This results in a brighter
picture at that instant. If the scene is dark, the coil is not energised. As picture information is
changing all the time, so does the SVM signal. If viewed on an oscilloscope, the output signal looks like
an inverted luminance signal.
correction can be adjusted by the end user via the picture menu. The drive signal is based upon the
luminance signal and controls the conduction of Q5407 and Q5408 depending upon the intensity of the
signal at that point of the scan/screen location. If there is a bright area at the edge of the picture,
the current in the SVM coil will increase and accelerate the electron beam. This results in a brighter
picture at that instant. If the scene is dark, the coil is not energised. As picture information is
changing all the time, so does the SVM signal. If viewed on an oscilloscope, the output signal looks like
an inverted luminance signal.
Page 61 of 80
Sharp Electronics (UK) Limited - March 2003
Revision 2
Click on the first or last page to see other 76FW-54H service manuals if exist.