I bought a Mini-DVI to VGA adapter from Monoprice.com and it put out the wrong colors, either blue or green. I discovered that if I pushed the adapter up in the slot, the display looked right. So I emailed Monoprice and they shipped me a new adapter. This new adapter has the same problem. It definitely wiggles in the slot in the Macbook, so I'm not sure if I have two defective adapters or if the output port on the Macbook is defective. Any way to figure it out besides taking it to a store?
I had a similar problem years ago with several monitors. Old style monitors relied only on the soldered joint of the VGA port to hold the weight of the cable, after a few years, the joint could break and then the screen would be green or blue of one of the pins were not connecting.
So the problem is that the signal is not connecting from the motherboard into the monitor. So you will need to do trial and error to sort it out.
1. The monitor is faulty Plug in to another monitor or display device with the same adapter, if the problem goes away then the problem is with the monitor or the VGA cable.
2. The connector is not plugging in properly If the connector feels loose, then it may not be connecting properly. Try blowing in the connector to ensure there is no debris and see if you can get it to plug in correctly.
3. The adapter is faulty You could have struck a bad batch of adapters and the second adapter could be faulty as well.
4. Loose or broken connection in the mac If you have tried all that and there still is a problem, then the connector on the Macbook might be loose, or the main board or video card might be faulty. For this one you will need to call apple or an authorized repairer.