Toshiba 4580, Service Manual

Page: 250 / 379

Mar. 1999 © TOSHIBA TEC 14 - 5 6570/5570 FUSER UNIT
Reference
1. A value other than 0, 1, 2, 3, 4, 5, 6, 7, 8 or 9 is never written in the Thermistor status counter.
• At the power on, if the heater is not turned ON and the copier goes into C41 CALL SERVICE, check the
Thermistor status counter to see if it is 2 or more. If it is 2 or more, be sure to check the thermistor and
heater lamp, and after repair, reset the Thermistor status counter (08-code 400) to 0 and then turn ON
the power switch.
• If the value of the Thermistor status counter is more than 10 (11, for example), it may be possible that
BC-RAM or the data in it have been destroyed by charger leaking, etc. In this case, check the guide
bias, high-voltage transformers, charger wires, etc. for any defects. Also, all the data inside BC-RAM
need to be rechecked.
2. Relationship between the output voltage and the fusing temperature.
• 200°C corresponds to approx. 2.5V and 0.25 V corresponds to approx. 40°C.
3. Relationship between heat roller surface temperature and thermistor-1 resistance.
Temperature Thermistor resistance Heater lamp state
Less than 200°C More than 0.8 k
Ω
ON
200°C 0.8 k
Ω
Maintains previous status
More than 200°C Less than 0.8 k
Ω
OFF
4. Temperature control at heat roller ends
During multicopying, the temperature at each end (no paper-contact area) of the heat roller normally tends
to rise higher than the controlled temperature of the paper-contact area. Therefore, the circuit is so de-
vised that if the temperature in the no paper-contact area rises to 240°C, the second thermistor detects
this, causing the heater to be turned OFF immediately regardless of the temperature in the paper-contact
area.
Copying (200°C)
Heat roller
temperature
distribution
Heater lamp
ON
OFF OFF
OFF
ON ON ON ON
Warm-up Standby (200°C)
°
C
200
OFF OFF
ON OFF