Cooling Fan Driver Circuit - Epson Stylus COLOR 900 Service Manual

EPSON Stylus COLOR 900/900N

2.3.9 Cooling Fan Driver Circuit

The cooling fan keeps the temperature of the printhead driver
transistors within their normal operating range. When the transistors
become too hot, it blows air through the heatsink to which they are
attached. The cooling fan also regulates the temperature of the
adjacent printhead pre-driver ICs (IC15 and IC16), located under the
heatsink. The figure below shows the cooling fan driver circuit block
diagram.
Figure 2-21. Cooling Fan Driver Circuit Block Diagram
The cooling fan driver circuit relies on input from two thermistors ("t1"
and "t2" in Figure 2-22). Thermistor t1 is attached directly to the heat
sink, while t2 is located on the main board between the printhead pre-
driver ICs. The table below shows the detected temperature and the
corresponding fan operation.
Table 2-15. Detected Temperature and Cooling Fan Operation
Cooling fan on
≥ ° ≥ °
t1 40 C or t2 50
Cooling fan off
≤ ° ≤ °
C t1 36 C and t2 42 C
IC1 processes the temperature detected by the thermistors every two
seconds, even while the printer is idle, and IC2 outputs a cooling fan
driver signal as shown in the table below:
Table 2-16. IC2 Output and Cooling Fan Operation
IC2 output (pin 176)
High (5 V)
Low (0 V)
Chapter 2 Operating Principles
Cooling fan operation
On
Off
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