Amstad Mega PC not switching down frequency for Megadrive display?

[tokyoracer]

Well, this is odd. At first I thought it could be an issue with the monitor but now I'm not so sure. I have both the original Amstrad branded one and an Acorn AKF50 which is apparently known to also work on it but both appear to show the same symptoms.

When the slider on the front of the machine is set from the PC side to the Megadrive side, it flicks a switch that I presume syncs the monitor down to 15khz so it can display the MD games correctly. I used to hear a high pitched tone when it did this but now it doesn't so I assume it is syncing to 30khz and that is what is causing the problem as shown in the pictures below.

Each shot is of each of the monitors. The display slightly varies but it seems to be the same symptom. Both monitors OFC, display the PC side totally fine.

Any thoughts what it might be that's stopping this from scanning down?

 

[AmigaNut08]

Could there perhaps be a relay that the switch triggers that may have gone cactus???

 

[tokyoracer]

I'm not sure, I don't recall seeing a relay on the motherboard. What would be useful is a user manual or better yet, a service manual showing what controls what but I can't find a thing on the net. There used to be one uploaded, albeit an apparently poor quality pdf one however all the links appear to be dead now.

 

[sputnik]

This link still works : http://www.fvempel.nl/amstradcg/metia/mega.pdf

Although it's just schematics not a troubleshooter