Hi,
we've got two new DrayTek 2830n installed to replace 2820n.
Since then couple of days a day the routers just freezing/crashing randomly. One of the routers is used as a WIFI (DHCP off) and other as a main router point.
Looks like DHCP issue on the main router, this is how the led on the router goes, http://postimg.org/image/qy44dhj81/
http://postimg.org/image/qy44dhj81/

If you have old firmware was an issue with wifi and android phones(HTC) ... it can be affect the wifi in general
As for the one using dhcp go at Lan>>general setup>>Lan 1>>details page and add manually any dns servers

Latest firmware is 3.6.4.1 for the sb model and 3.6.4 for the db model ... if you want give a try (make sure to use the correct one ... the sb is for single band and db is for dual band models)
ftp://ftp.draytek.com/Vigor2830/Firmware/