JVC 250 service manual Raster Timing Generator PCB LEDs

Chapter 7---Troubleshooting

Raster Timing Generator PCB LEDs

Band LEDs

The range horizontal scan frequencies accepted by the Model 250 projector is divided into four “bands”. The four LEDs (A, B, C, & D) toward the front of the projector on the Raster Timing Generator PCB indicate which range of horizontal scan frequencies the input source is operating. The four bands of horizontal frequencies are

Band A = 15-25 kHz

Band B = 26-29 kHz

Band C = 29-56 kHz

Band D = 56-90 kHz

Only one of these LEDs will be illuminated green at one time. As an example, if the input source horizontal scan frequency is 64 kHz, Band D LED would be illuminated green.

Sync Type LEDs

The five LEDs, toward the rear of the projector on the Raster Timing Generator PCB, indicate the sync of the input source. As an example, the SEP LED would be illuminated green if the input source had separate horizontal and vertical syncs. The following list gives a brief description of the each LED and its associated sync type.

SEP - Separate horizontal and vertical sync inputs.

COMP -Composite (Red, Green, Blue, Horizontal, and Vertical signals all combined into one signal).

INT - Internal sync means there is no input source sync signal present so the System Controller PCB generates an internal sync at a horizontal scan rate of 33.7 kHz and a vertical rate of 59.7 Hz interlaced.

GRN - Sync-on-Green sync is where the horizontal and vertical sync signals are combined with the green image signal.

PLL - Phase Locked Loop is the circuitry that locks onto the horizontal sync. This LED indicates that the projector has locked onto the horizontal sync signal.

One of the first four LEDs should be illuminated indicating the type of sync used by the input source. The fifth LED (PLL) should always be illuminated when the projector is operating except during input source changes.

7-8 Model 250 Service Manual