Ricoh FT7770 Service Manual page 92

30 '89
April,
Drum Temperature Compensation (V4):
When the switch on the bias power pack is on, the CPU monitors the drum
temperature through a thermistor (TH-2), and it increases or decreases the
bias voltage to compensate for temperature induced variations in drum sen-
sitivity. The temperature compensation is -6 volts for each degree increase
in drum temperature and is effective from 15°C to 45°C.
However, if the bias switch is off, the CPU assumes a drum temperature of
30°c. The power pack does not compensate for temperature, and V4 be-
comes +90 volts.
-Total Development Bias (Vt)-
The total bias applied to the development roller sleeve is the sum of the
base bias and the two compensation factors.
Thermistor SW
ON
OFF
The increase in development bias between 15°C and 45°C
Vt (manual mode)
V 1 + V 3 + V 4
V 1 + V 3 + 9 0
Vt (auto mode)
V 2 + V 2 ' + V 3 + V 4
V 2 + V 2 ' + V 3 + 9 0
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