tv picture shaking up and down!

[churkus]

OK I have this Sanyo Scart TV that I picked up from a friend who was about to bin it. Its model is ce28dfn2b

It is exhibiting a strange behaviour in groovymame at some resolutions, from what I have observed it appears to be in 300 range of horizontal resolutions i.e 320x240, 384x224 etc. Other resolutions are solid and stable.

What will happen is that when I run a game in these resolutions, the screen shakes/jumps up and down by a few mm every few seconds. This can become quite nauseating after a while!.

The strange thing is, when I try these same resolutions in ArcadeOSD, they are perfectly still!.

This never happened on the Sony tv I had before, as far as I remember at least!.

Any ideas?

[Calamity]

Hi churkus,

Check if the shaking happens at all vertical refresh rates or only at some of them (e.g. above a certain value). If it's refresh related, we will limit the range to avoid the problematic values.

[churkus]

HI Calamity,

As always, thank you for your ongoing help with GM .

I havent had much time recently to play on the mame box. Had a bit of time last night, so I looked at this issue again.

Ok, firstly it definately is only occuring in the 300 range of horizontal resolutions. Secondly (if it matters), it doesnt seem to happen immediately when you switch the TV on, it starts after about 20 minutes the TV has been on, so im guessing some kind of frequency control resistor gets a temper after a while!.

The main thing I have discovered is that it doesnt matter of the hz, it is the khz of the game that causes this shaking!. The game can be 57, 58,59,60,60.5 hz and have shaking. But it only shakes when the khz of the game is between 15630-15900 (roughly)!!!!!!!!!.

So to prove this was the issue, I edited the default modeline in vmmaker and raised the starting khz range to 157200. I also copied the same line to crt_range0 in mame.ini, putting 0,0 at the end for interlaced modes. And now guess what no more shaking!.

But is this the right solution to my problem?. If a game is supposed to run at 59.493 hz and 15.635khz, then what happens if it runs at 59.493hz and 15.732 khz for example?. Does the speed of the game change or any anomalies like that?. THis is my only concern really.

thanks for your help.