F. Fixing Heater SSR Error Detection CircuitThe safety circuit for the copier’s fixing heater SSR uses the following signals toidentify an error: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 sameway.Heater ONThe CPU causes the SSRON signal to go ‘0’, and the MHRD signal goes ‘1’ to turnON the heater. At this time, the fixing feeding unit detection signal (FFURLS), powerswitch ON detection signal (MSWD), and front door open detection signal (FDOD) are‘0’.Heater OFFThe CPU causes the SSRON signal to go ‘1’, and the MHRD signal goes ‘0’ to turnOFF the heater.SSR ErrorIf the main heater ON detection signal (MHOND) is ‘1’ when the CPU on the DCcontroller PCB is not generating the fixing main heater drive signal (MHRD), as by thegate array q, or if the main heater ON detection signal (MHOND) is ‘0’ when the CPUon the DC controller PCB is generating the fixing main heater drive signal (MHRD), asby the CPU w, an SSR error is identified and the CPU on the DC controller PCBindicates an error code.At the same time, the power switch OFF signal (PWOFF) is caused to go ‘0’ to cutoff the AC circuit. When the power switch is turned OFF, power to the heater will be cutoff; however, since the DC controller PCB is supplied with power for a specific period oftime (see descriptions on the power supply), the power supply PCB sends the powerswitch ON detection signal (MSWD) to prevent activation of the relay inside the powerswitch in response to the PWOFF signal.Since the copier’s main heater ON detection signal (MHOND) is ‘1’ even under thefollowing conditions, the SSRON signal is kept ‘0’ to avoid wrong detection of an SSRerror:1.When the fixing/feeding unit has been slid out (FFURLS signal: 1);2.The front door is opened (FDOD signal: 1); and3.The power switch has been turned OFF (MSWD signal: 1).COPYRIGHT © 1997 CANON INC. CANON NP6045 REV. 1 MAR. 1997 PRINTED IN JAPAN (IMPRIME AU JAPON)CHAPTER 6 FIXING SYSTEM6-10
