Exposure Lamp Control Circuit - Ricoh Robin Service Manual

24 June 1994

3.7 EXPOSURE LAMP CONTROL CIRCUIT

Main Board (PCB1)
B
TP111
Zero
(EXPO)
Cross
CN107-1
E
Feed back
signal
CPU
0V
+24V
C
24V
0V
Trigger Pulse
AC power
Zero cross
Trigger pulse
Lamp power
Feedback
signal
The main board sends lamp trigger (LOW signal) pulses to the ac drive board
from CN114-3. PC401 activates TRC401, which provides ac power to the
exposure lamp, at the lead edge of each trigger pulse.
The voltage applied to the exposure lamp is also provided to the feedback
circuit. The feedback circuit steps down (TR401), rectifies (D404 ∼ 407), and
smoothes (zener diodes and capacitors) the lamp voltage. The CPU monitors
the lowest point of the smoothed wave (feedback signal), which is directly
proportional to the actual lamp voltage.
The CPU changes the timing of the trigger pulses in response to the
feedback voltage. If the lamp voltage is too low, the CPU sends the trigger
pulses earlier so that more ac power is applied to the exposure lamp. This
feedback control is performed instantly; so, the lamp voltage is always stable
even under fluctuating ac power conditions.
The voltage applied to the exposure lamp can be changed with SP48 (Light
Intensity Adjustment). The ADS voltage adjustment (SP56) must be done
whenever the light intensity adjustment is done.
AC Drive Board (PCB2)
R404
R405
CN114-2 CN401-7
VR401
C401
R403
CN114-1 CN401-8
R401
CN114-7 CN401-2
PC401
CN401-6
CN114-3
A
B
C
D
E
Feedback
2-19
ZD ZD
401 402
D401
D404
~D407
ZD
ZD
403 404
R406 220V Only
TR401
R411
TRC401
CR401
L401
L402
R413
OPTICS
T402
CN421
240V
CN419-1
Thermo-
220V
fuse (TF)
Exposure
Lamp A
(L1)
D
AC115V
CN419-2
AC220V
AC240V
C411
T407