Indi 1200 AGA MK3 and Acorn AFK50/Microvitec M1438S/CEI A1962 - works with all other monitors but this one

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Don't Panic. Please wash hands.

    Hi.

    I've recently purchased the AGA MK3 and it works. I can use it with a 19inch Dell CRT and have a good picture. However, my CRT (Acorn AFK50 - rebadge MicroVitec) will only display a very scrambled picture, as seen in the attached pictures. The monitor works, for sure. It is supplying a decent picture via the Amiga's native RGB port at 15Khz, but via the MK3 only gives me this scrambled picture.


    Any thoughts?


    Thanks

    I'm assuming that you've chosen a mode that the monitor actually supports (not exceeding the max. HSync frequency of the MicroVitec monitor).


    I remember that when the first German "Amiga" incarnation was active (1995/1996), they also used MicroVitec monitors and re-badged them with Amiga. It's probably why you're trying to connect it to the Amiga, right?


    That was the time when I developed my first commercial product, the Graffiti card. I had serious trouble making it work with one of the prototypes and had a solution adding a driver to the HSync output. So I know that these monitors are special, maybe even violating the standard.

    I suspect that the monitor puts a heavy load on the HSync signal and does not acept the 3.3V signal that Indivision AGA MK3 outputs. If you're a little into electronics, you could try to buffer the HSync signal and see if it makes a difference. I won't be able to do anything about it, and to be honest, don't really see the need, as we didn't have any report of a non-working monitor in all these years, indicating that the monitor violates the standard with it's load and/or switching threshold.


    Jens

    Indivision ECS V3 has a pretty strong 5V sync driver. If your monitor does not show a picture with that, you may just play with sync polarity, as monitors of the time have used that as their sole information source for the frequency range to expect. The MicroVitec monitor may play nice with negative sync for 15kHz signals, but may also require positive sync for 31kHz horizontal frequency - or vice versa. Just play around with it; chances with Indivision ECS V3 are *very* high, and once you've found a mode that works with ECS V3, you can apply that to the AGA MK3 version as well and see if the monitor accepts it at 3.3V level.


    Jens