Independent 50hz/60hz adjustments with trinitron KV21CL10B

[govenori]

Hi there,

Here it's not a post about an issue or something wrong, it's actually about something quite cool and useful.

I bought recently for nothing a Trinitron tv model kv21cl10b with about 1500 hours of use. As usual, it was essential to adjust the geometry via the service menu, which I started to do by plugging an rgb 50hz signal to make the tweaks (A switched megadrive1, pal/ntsc). As usual with trinitron.

As I was working on this, I noticed quickly that the adjustments made at 50hz were not saved once the signal was 60hz. After trying to adjust, with nothing plugged or with no video signal, I finally tried to make adjustments directly with an rgb 60hz signal, without believe in it too much.

It appeared that it worked. The geometry adjustments made with a 60hz (ntsc then), were correctly saved. That's useful, as I usually use the megadrive in 60hz.

What it's even more useful, is that the geometry settings appear to be different in the service menu as I plug a pal 50hz, or an ntsc 60hz signal. Both can be modified separately.

What's the use you may ask ?...it's true that it's better to play megadrive games at 60hz.

Well, some games like Gunstar Heroes or Alien Soldier are adapted for pal, it means they run at the "normal" speed, musics are also at right tempo as well, but we got these infamous margins at top and bottom. Running them in 60hz is too much, above all for the musics. But we have the correct image.
So here, it's possible to adjust the 50hz image by stretching it to get rid of the margins by using the VSIZ adjustment.

I don't know if it's bad for the tv to vertical stretch the 50hz image like this, but well, it allows me to do it, so...why not. And it has no influence on the 60hz signal, they are independent from each other.

There is in the service menu, something called PAL/NTSC IDENT SENSITIVITY (CHSE). Is this phenomena related to this function ? Mystère...

Voilà. As I said, it's a quite practical thing, but also a little bit mysterious, so if anyone have an explanation, let's share it !

Thanks