Tektronix MSO70000 Series Service Manual page 36

Theory of Operation
Power System
Fans
2–12
A 250 W power supply generates a switched 12 volt bulk supply as well as a
5 volt standby supply.
No switch completely disconnects the line power from the instrument. The power
switch controls the power to the instrument through the COM-E board circuitry.
When the instrument is in the "power off" condition, there is still a low power
standby circuit to allow the system to monitor the power switch.
There are two instrument fans: the system fan, which is mounted on the rear
chassis, and a smaller fan, which is mounted on the COM-E module. For cooling,
the system fan draws air into the instrument, for a positively pressured instrument.
The system fan is controlled by an embedded processor on the Main board and is
regulated by monitoring the temperature of the Analog acquisition board circuitry.
Cooling air enters the instrument through specific locations on the covers, where
it flows directly over the heat sinks of each high wattage component. The COM-E
fan cools the COM-E module.
MSO70000/C, DSA70000B/C, DPO70000B/C, DPO7000, MSO5000, DPO5000 Series