Ricoh M5 Service Manual page 75

— Exposure Sensor —
The exposure sensor measures the intensity of the light output by the exposure lamp and provides a
feedback signal to the main board.
in response to the light intensity of the exposure lamp.
tions in photodiode current to voltage changes and applies it as a feedback signal at CN104-2 on the
main board.
— Compensation Processing –
Compensation processing consists of modifying the control signal in response to the feed-back sig-
nal. This processing is carried out by the CPU .
If the exposure light intensity is too LOW, the CPU increases the ratio T1 /T. (The width of T1 is
increased.) If the light is too strong, T1 /T is decreased.
is fixed at 1ms.) Since power is provided to the lamp during T1, the lamp brightness changes
accordingly.
The feedback circuit keeps the exposure lamp output very stable.
almost at the same time offset by a change in T1 width.
tant. Feedback compensates for fluctuations in the ac power supply, variations in lamp output due
to lamp temperature, and for the slow
Image
Density
Indicators
T1
Feedback Signal
– Service Call Condition –
The CPU monitors the exposure lamp control signal to detect exposure malfunctions. If the ratio of
T1 /T becomes greater than 0.95 ms or less than 0.15 ms, the CPU stops the copier and lights self-
diagnostic code El.
The sensing element is a photodiode (PD). It regulates current
decay in exposure lamp light output over the lamp's lifetime.
1 2 3
0 . 2 0 0 . 2 7 0 . 3 3
1 3 . 1 6 . 2 0 .
3 - 1 8
The amplifier circuit (IC1 ) converts the varia-
(T1 can vary from 0.2 ms to 0.95 ms and T
Any change in light intensity is
The voltage observed at CN104-2 is cons-
4
5
0.4 0.5 ms
2.4 3.0 V
May, 25, 1985