How to eliminate horizonal overscan when no service adjustment?

Peabody · 2007-06-06T23:28:48+00:00

It's a JVC AV-27920 television, circa 1995 or so.I understand that manufacturers deliberately build in overscan so that any shrinkage resulting from CRT aging won't produce visible black borders. But I would like see all the picture.The service menu has adjustments for vertical size and position, so I assume I can use those to get rid of all, or at least most, of the vertical overscan.But there is no width or horizontal size adjustment, only horizontal position.So I would like to think about making changes to the circuit that would give me this adjustment.In theory, I guess I don't want to change the horizontal frequency, just the relationship between the yoke and the guns on each line. So maybe instead of an actual width adjustment, it would work well enough to change where the scan begins, or ends, and then use the position adjustment to center it again.And I wonder if I could do this by adding additional inductance in series with the horizontal deflection yoke, with the idea that more inductance would slow down the rate of change in the yoke, so that the beams don't progress horizontally as fast as before, and therefore finish the line before reaching the edge of the screen.Is this all crazy? It doesn't seem like it should be. I mean, width/size adjustments are not unknown in the modern world, so it should be possible to insert one. I just don't know enough about televisions to know how to do it.I would appreciate any suggestions anyone might have.Oh, and I do have the schematic. Sams 4080.

Jun 06, 2007 20 Replies

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Franc Zabkar 19 years ago

On Mon, 11 Jun 2007 17:39:21 -0500, Peabody put finger to keyboard and composed:

The yoke current (0.5A - 1A?) flows through L521 and C526, not R526. In fact I'm still uncomfortable about the circuit. AFAICS, a traditional horizontal deflection circuit doesn't need R526. Can someone tell me what this resistor does? I understand that R530 and C527 are required to dampen the ringing in L521, and C526 blocks the DC path through the yoke.

As for where to place the additional width coil, put it between L521 and C526.

- Franc Zabkar

Please remove one 'i' from my address when replying by email.

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How to eliminate horizonal overscan when no service adjustment?

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