It is a CGA and MDA card. The RCA connector tells me its CGA compatible and the 16.257MHz clock crystal tells me that it is MDA compatible. The 16KB of RAM also informs me that it is not Hercules compatible, because that requires 64KB. I would suggest that the card's bracket switches determine the monitor type/mode if JP1 is set to hard, otherwise the motherboard switches on the PC or XT system board would determine the monitor type. Using the DOS MODE command can also be helpful. I would use the RCA out when testing the switches. Among the common variety of selections are CGA 80x25 color text, CGA 40x25 color text, MDA 80x25 text, CGA 80x25 B&W text and CGA 40x25 B&W text. "B&W" only has an effect on a color composite monitor.

Thanks for the info, you clearly have some real guru knowlage on these chips. I guess i'l have to try and find a compsite phono for the other display. I suppose if it displays something on my TV, that would suggest it's the 5151 at fault.

EDIT: Here it is on my TV, the screens differe, looks like it's posing ok (reckon the white bits is the text informing it's checking the RAM).

The 2 pics show the result of selecting DIP switch "1" on and off. the other 3 seem to do very little (if anything).

Just to add, this is the display on the 5151 (with the contrast and brightness up anyway):