Looking at the Amstrad CPC 6128 there are 3 connections on the left side for audio, joy stick and cassette,on the back there is a printer port, expansion port, 5volt power, video in, power switch, volume control and external floppy drive port. There is also a cable hanging out the back which connects to to a dedicated monitor to provide 12volt power to the floppy drive, along with 2 other cables to provide 5volts and video. 

I can connect 5volt supply, there is a tag underneath the machine which tells me it takes 1.7amps.  I dont need the 12v yet as I just want to check if the machine works. Turning it on I get the power led lit up and a click from the speaker. I dont have a monitor so the only way to check if its actually working is to press the DEL key and it should beep indicating there is no charactors to delete, this works, but as a further test I press a charactor key a few time then the DEL key the same amount of time before it beeps, this works.

I needed a converter to allow me to connect a HDMI monitor to the 6128. The computer, like many of this era output an RGB signal to a CRT monitor. In Europe many video devices have a SCART connection (or had)  which allowed you to connect a RGB or composite video source to the device so it is possible that some of these monitors are still around or at least a scart cable.  I live in Australia, we didnt use SCART (although I have seen a cable somewhere) so I have to get a converter, a SCART cable and a 6 pin DIN plug. I ordered these on ebay over xmas so it was going to take awhile.