Thanks I have got all the updates applied and have now swapped my CSV-5300 for a CSV-4000 with new cables to see if the updated technology would help but I’m still stuck with only 2 displays working concurrently at any resolution. My configuration sequence is
Surface Pro 3-i7-500GB powered up.
mDP-DP passive adaptor connected to Surface mDP port and CSV-5400 powered up.
CSV-5400 DP Port 1 DP-HDMI passive adaptor connected to Dell ST2420L display and set as main display. Surface display disconnected in display settings.
CSV-5400 DP Port 2 DP-DVI passive adaptor connected to Dell ST2210 display.
Duplicate desktop in display settings then extend desktop to Dell ST2210. Both displays working OK at 1920 x 1080 resolution so far.
CSV-5400 DP Port 3 DP-DVI passive adaptor connected to Dell 2009W display. Displays all recognised in display settings but any attempt to duplicate or extend the desktop to the 3rd display fail whatever the resolution. The same happens in any combination of ports on the CSV-5400 or order the displays are connected in.