2009 iMac fails to identify external display

Hi there!

I have an old LG Flatron W2241S (VGA only, 1680x1050) connected to a 2009 21" iMac running Mavericks through an original Apple mini-Display port adapter and VGA cable. It fails to identify it properly, showing as a generic VGA display and offering only the 4:3 set of resolutions.

The funniest thing is, I also have a 2009 MacBook Pro, running an exact copy of the system (user, applications, preferences, just a clone) and it works just fine. I used to work around this by using SwitchResX, but eversince I upgraded to Mavericks it doesn't work anymore. Even if I jot down every parameter from my working MBP and replicate the configuration on the iMac, it won't accept it, and will keep listing it as "Not installed".

Any help? I was thinking there might be a way to force the identification of a given piece of hardware through some config file or plist. Some way to tell the system "if you find this unknown display, just assume it's this specific model from this specific vendor".

Thanks a lot and greetings from Madrid 🙂

Pablo