Multi-display - one monitor active but blank

[Oliver Elphick <olly@lfix.co.uk>]

I have two monitors; the second one sometimes comes to life but is
usually blank. However, the system thinks that it is active and
displaying.

The primary monitor is a Samsung 24" and the secondary (usually non-
functioning) one a Mirai  - Chi Mei Optoelectronics 22".  Just
occasionally the second monitor comes up and can be used normally, but
once the displays are turned off by the screen saver, it remains blank
when the display comes back.  However the "Displays" utility says that
it is in use.

Previously I avoided the problem by turning off the screen-savers and
leaving the monitors turned on 24 hours a day, but I have just
installed Debian (instead of Mint) and the problem has come back.

Any ideas where to start to solve this, please?


-- 
Oliver Elphick
Lincolnshire, England