JVC 250 service manual Electronics

Chapter 5---Electronics

CRT Mechanical Focus

The CRT Mechanical focus is factory-set and normally will not require additional adjustment unless a CRT has been replaced. After replacing a CRT, reset the mechanical focus. After completing the CRT installation and mechanical focus, check the other CRTs for convergence and shading.

Tools Needed

1.5-mm Hex-head wrench

#0 Pozi-drive Phillips-head screwdriver

To adjust the CRT Mechanical Focus:

1.Remove the rear cover.

2.Pull the Interlock Switch for the rear cover up to the Service Mode position.

3.Power the projector ON and allow it to stabilize for at least 15 minutes.

4.Tilt the Electronic Module to the full up position.

5.Select the Focus pattern (test pattern #6).

6.Zoom the Projection Lens to the widest angle (largest image) and adjust the Projection Lens focus for the sharpest image of the Focus test pattern.

7.Loosen the two setscrews (see Figure 5-29) near the top of the CRT sleeve using the 1.5-mm Hex-head wrench.

8.Loosen the CRT focus lock screw located on the Guide Plate at the top of the CRT shield (see Figure 5-29). The CRT is now free to slide.

9.Grasp the CRT thumbscrew (see Figure 5-29) and slide the CRT forward and backward until the image is focused as sharply as possible (be careful not to loosen the CRT thumbscrew, which could allow the CRT to rotate).

10.Tighten the setscrews first, then the CRT focus lock screw.

NOTE: Tighten the setscrews before tightening the focus lock screw. If the setscrews are loose the focus lock screw can slightly defocus or rotate the CRT as it is being tightened.

11.Repeat the above steps for the Red and Blue CRTs.

Model 250 Service Manual 5-53