secondary screen only works until login

[Dave Stevens]

Hi,

I'm using 16.04 on a Toshiba laptop. I want to use a secondary display,
a Samsung SyncMaster 712n. I have it connected to the Toshiba's
external VGA port. The display powered up and showed system activity
right up until the automatic user login took place. I had the system
configured to log me in without asking for a password. When the login
took place the secondary display went blank. The system control panel
shows an unknown secondary display.

In an attempt to see where the problem lies I made a new (second) user
with a password and required a credential check at login. When I log in
as the new user the secondary screen mirrors the main laptop screen and
continues to work until I logout then log back in as the previous
(admin) user, then it blanks.

I suppose if I knew more about the graphic setup this would tell me
where to look for more info but I don't. 

Anyone have a suggestion about where to look?

Dave



-- 
In modern fantasy (literary or governmental), killing people is the
usual solution to the so-called war between good and evil. My books are
not conceived in terms of such a war, and offer no simple answers to
simplistic questions.

----- Ursula Le Guin