Sony WRT-810A Operating Instructions Manual page 6

The unit is designed for use in an ambient temperature range of 0°C
to 50°C (32°F to 122°F).
Do not place the unit on or near a heat source such as lighting
equipment or a power amplifier, or in a place subject to direct sunlight
or excessive moisture. In such places, the external finish or internal
parts of the unit may be damaged.
If the unit is used in a very humid or dusty place or in a place subject
to an active gas, clean its surface as well as the connectors with a
dry, soft cloth soon after the use. Lengthy use of the unit in such
places or not cleaning it after its use in such places may shorten its
life.
When cleaning the unit, never use organic solvents such as thinners
or benzine, which will damage the finish of the unit.
The unit has been factory adjusted precisely. Do not tamper with its
internal parts or attempt to repair it.