Motorola VT-71: blanking + schematic

[david winter]

Hi,

I'm finishing the restoration of a Motorola VT71 (chassis TS4-D).
I get a quite nice picture however there is a terrible raster effect over the picture caused by the beam going back to initial position for next frame.

I wanted to know if anybody knows how to remove the raster and also how to remove the teletext causing some static on the top of the picture ?

Also, the contrast works somehow but will eventually alter the picture quality when put to the maximum.

The most important is to remove the raster effect, the rest can be done later.


Thanks !

[leadlike]

The Motorola vt-71 was manufactured without any provision for vertical blanking, hence the terrible retrace lines you observe are "stock" to the original set. There are methods to eliminating these, though, but I don't have the link handy. I'm sure someone will chime in with it.

As far as the teletext is concerned, I just simply increased the vertical size until this was offscreen. I'm not sure what you're saying about the contrast control, but I will say that on mine the effect is very strong when set to it's peak-almost pure black and white with no intermediate shades. This effect is certainly unique among my sets.

[bandersen]

Check this out: http://antiqueradios.com/forums/viewtopic.php?t=12044

I think I'll try it later tonight on a TS-4H chassis VT71.

[david winter]

WOW ! Thanks for this link ! I'll test that tomorrow.

David.