Ssr Error Detection Circuit For The Fixing Heater - Canon NP6251 Service Manual

CHAPTER 6 FIXING SYSTEM
F. SSR Error Detection Circuit for the Fixing Heater
The machine's safety circuit for the fixing heater SSR uses the following signals sent
to the DC controller PCB:
1. Fixing main heater drive signal (MHRD)
2. Main heater ON detection signal (MHOND)
Figure 6-107 shows the main heater only, but the sub heater is controlled in the same
way.
Heater ON
The CPU causes the SSRON signal to go '0', and the MHRD signal goes '1' to turn
on the heater. At this time, the fixing assembly feeding unit detection signal (FFURLS),
power switch ON detection signal (MSWD), and front door open detection signal (FDOD)
are '0'.
Heater OFF
The CPU causes the SSRON signal to go '1', and the MHRD signal goes '0' to turn
off the heater.
SSR Error
If the main heater ON detection signal (MHOND) is '1' when the CPU on the DC
controller PCB is not generating the fixing main heater drive signal (MHRD), i.e., gate
array detection , or if the main heater ON detection signal (MHOND) is '0' when the
CPU on the DC controller PCB is generating the fixing main heater drive signal (MHRD),
i.e., CPU detection
code.
To cut off the power to the AC circuit, the DC controller causes the power switch OFF
signal (PWOFF) to go '0'. When the power switch is turned off, the power to the heater
will be cut off; however, since the power to the DC controller PCB is maintained for a
specific period of time, (see p. 7-9), the PWOFF signal is kept to prevent the relay inside
the power switch from turning on, thereby locking the power switch ON detection signal
(MSWD) from the power supply PCB.
Since the machine's main heater ON detection signal (MHOND) will go '1' under the
following conditions, the SSRON signal is kept '0' so as to prevent detecting an SSR
error wrongly:
1.When the fixing feeding unit is slid out (FFURLS=1).
2.When the front door is opened (FDOD=1).
3.When the power switch is turned off (MSWD=1).
6-12
COPYRIGHT © 1997 CANON INC.
, the DC controller will identify an error in SSR and issue an E
CANON NP6350/NP6251 REV. 0 JULY 1997 PRINTED IN JAPAN (IMPRIME AU JAPON)