JVC 250 service manual Horizontal Vertical Deflection PCB - Operation

Chapter 5---Electronics

Horizontal Vertical Deflection PCB - Operation

The Horizontal Vertical Deflection PCB consists of a RGB horizontal deflection amplifier and separate vertical deflection amplifiers.

The Horizontal Deflection Amplifier

The horizontal deflection amplifier is a switching mode power supply that varies according to the input horizontal sync frequency. The horizontal supply generates the sawtooth current-driven waveform that drives the horizontal deflection coils on the CRT. The sawtooth current waveform creates the raster on the CRT. The horizontal amplifier also generates the retrace waveform portion of the raster.

The horizontal deflection sawtooth waveform is modulated by other waveforms that perform geometric correction such as Pincushion, Keystone, Horizontal Centering, Horizontal Linearity and Horizontal Width adjustment. The Width Control voltage also goes to the Convergence Deflection PCB to adjust the geometric correction parabolas.

The H_F2V signal converts the input horizontal scan frequency to a voltage that switches from one band (see explanation of bands in the Raster Timing Generator PCB Operation section) to the next depending on the horizontal scan frequency. This adjusts the retrace time to correspond to the input horizontal frequency. The output of the horizontal supply is H_OUT_SUPPLY that goes on to the Scan Reversal PCB.

CRT Protection

The Horizontal Vertical Deflection PCB uses the H_LOCK+, H_LOCK- and DEFL_OK signal to protect the CRTs from being damaged if the deflection waveforms are lost. Refer to the CRT Protection section in Chapter 9 for a complete discussion of these and all the signals associated with CRT Protection.

The Horizontal Vertical Deflection PCB receives the DEFL_OK signal from the Scan Reversal PCB indicating the presence of the horizontal and vertical deflection waveforms. If there is a failure of any of the Deflection Yokes (horizontal or vertical), a current sense line on the Scan Reversal PCB forces DEFL_OK low. On the Horizontal Vertical Deflection PCB, the DEFL_OK signal becomes /SWEEP_OK and is sent to the Video Amplifier PCB where it shuts down G1. If DEFL_Ok is forced low, or if /H_ENA is forced high, /SWEEP_OK goes high. The /SWEEP_OK goes to the Video Amplifier PCB. If it goes high, it shuts down the G1 voltages and G2 Regulator circuit (see Troubleshooting, CRT Protection section).

Vertical Deflection Amplifier

The vertical deflection sawtooth waveform is generated on the Convergence Deflection PCB and timed to the vertical sync by the V_DRIVE signal from the Raster Timing Generator PCB. The Convergence Deflection PCB sends this waveform along with a parabola waveform V_PARAB to the vertical deflection amplifier on the Horizontal Vertical Deflection PCB. The Horizontal Vertical Deflection PCB takes V_RAMP, amplifies it and adds geometric correction with

Model 250 Service Manual 5-25