Canon NP2120 Service Manual page 89

D. Error Detection Circuit
(NP2020)
The error detection circuit is found on the DC
controller PCB and serves to monitor the fixing
temperature and scanning lamp; Le., abnormal rises
of the circuit causes the relay (RLl) to go OFF,
thereby cutting the supply power (AC) to the fixing
heater and lamp regulator.
2. Mechanism
Whenthevoltageofthethermistorreachesabout
1.0 V because of a rise in the temperature of the
fixing roller, the output of the No. 1 comparator of
detection circuit
(DC controller PCB)
ning lamp ON signal) at all times as long as the
scanning lamp is ON.
tor of Q309 to generate '1'. thereby charging the
thereafter: and output '1' of the No. 2 comparator is
sent to the negative (-) input side of the No. 3
comparator. As a result, the output of the No. 3
comparator of Q309 goes '0'.
thereby causing the relay (RLI) to go OFF.
errordetection circuit by turning it OFF and then ON.
Figure 3-45
C A N O N NPZl2O/ZMO RN.0 MNY 1990 PRINTED IN JNPAN IIMPAIME RU JAPONI
The lamp regulator generates LIGHT=l (scan-
The above conditions cause the No. 2 compara-
C333 becomes fully charged about 20 seconds
T h e above conditions generate ACOFF=O,
The copier can be reset after activation of the
3-47