SERVICE MANUAL - O. Rensch OHG
SERVICE MANUAL - O. Rensch OHG
SERVICE MANUAL - O. Rensch OHG
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2DC<br />
(2) Heater lamp control circuit<br />
Activation of the heater lamp is dominated by the HEAT signal which is derived by the engine CPU (U1) at its pin #74. When<br />
its level is high, transistor Q8 turns on, photo-triac PC2 and triac TRC1 turn on simultaneously, and the heater lamp is<br />
applied with the primary AC voltage in turn.<br />
Switching of triac TRC1, as affected by the HEAT signal is made in synchronization with the zero-cross signal ZCROSS<br />
which is generated by the power supply unit. The zero-cross signal detector watches the transition of alternating plus and<br />
negative current and detects the zero crosses. This detector derives the resultant ZCROSS signal at its pin #43 of the<br />
engine CPU (U1). Since abrupt change in the current flow can be significantly avoided by synchronizing triac TRC1 with the<br />
zero-cross signal, the possibility of noise due to the primary AC supply is greatly reduced.<br />
Engine board<br />
P72/ANI2<br />
98 THERMA<br />
CPU<br />
U1<br />
GND<br />
R52<br />
+5V<br />
U6-1<br />
2<br />
− 1<br />
3 393<br />
+<br />
Heater lamp control circuit<br />
Q8<br />
R57<br />
PDL3/AD3<br />
74 HEAT<br />
GND<br />
GND<br />
GND<br />
43 ZCROSS<br />
P05/INTP2<br />
Thermal cutout<br />
Heat roller<br />
Heater lamp<br />
AC input<br />
Triac<br />
(TRC1)<br />
Power supply unit<br />
+24 V<br />
Zero<br />
cross<br />
signal<br />
detection<br />
circuit<br />
(PC2)<br />
Photo-triac<br />
Bias<br />
board<br />
High<br />
voltage<br />
board<br />
Thermistor<br />
Figure 2-3-4 Heater lamp control circuit<br />
2-3-4
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