VIEWSONIC VS13394 - Manual (Page 62)

4. CAUTION: To reduce the risk of fire, use only the
enclosed DC 5V adaptor or USB cord.
5. CAUTION: Do not remove the cover (or back).
There are no user-serviceable parts inside. Refer
servicing to qualified service personnel.
6. CAUTION: To ensure reliable operation and to
prevent overheating, provide adequate ventilation
for your eBook device and keep it away from heat
sources. Do not locate it near heat registers or
other heat-producing equipment. Provide for free
air flow around the eBook device and its power
supply.