S E R V I C E
Whirlpool Europe
MT 263/WH
27.01.1998 / Page 9
Customer Service
8538 263 53291
Doc. No: 4812 714 12124
VKK, Display and Buzzer.
El Crisp:
Zener diode 6126 and transistor 7125 generates a stabilised voltage of approximately -22V DC.
This voltage supplies the midpoint of the transformer filament winding and the buzzer.
VKK voltages is supplied by a voltage divider (3127 and 3128) and emitter follower 7128.
Fuzzy Crisp, Convection and Fuzzy Crisp Convection:
The transistors 7172 and 7171, and the zener diode 6172 stabilise the VKK and buzzer supply voltage to
approximately -34 V.
The midpoint of the transformer filament winding is feed via zener diode 6171.
Relay Driver Circuits
To prevent the relays from being activated if the processor is hung up, the relay driver is ac coupled. This
means that a pulse train on output P20 is necessary to activate the relays.
When any relay shall be activated the output of P20 will deliver pulses t low = 229 us and
t high = 15 us.
Transistor 7232 and 7134 is switched on when P20 goes low and they are switched of when P20 goes high.
Capacitor 2232 and resistor 3232 forms an integrator. The voltage over capacitor 2240 is equal to the average
voltage over the relay coils. When transistor 7134 is switched of the current in the relay coils continue to flow
through the diodes 6133.. The negative pole of 2232 goes to plus 0,6 V. If the voltage over 2232 exceeds the
zenervoltage of 6236 the zener diode will conduct and when P20 goes low and the transistors 7232 and 7134
can not switch on.
Transistors 7131, 7130, 7161, 7163 is used to switch on MW, Grill, FC heat and the FC fan
relays. The El Crisp does not contain the FC relays.
The F/L relay has to be on to enable any other relay to be activated.
When the door is open and the fan supply is interrupted by the secondary door switch, the frequency of the
pulse train on P20 is 340 Hz when the F/L relay shall be turned on. the dutycycle is 75 % (low) on the El Crisp
control and 58 % (low) on Fuzzy Crisp, Convection and Fuzzy Crisp Convection.
50 Hz Sensing Circuit
The 50Hz-signal is taken from the secondary winding of the mains transformer, before the rectifier. The
voltage is divided by 3210 and 3211 before it is fed to transistor 7211. Port G13/R32 of the micro processor is
normally high (Vss), except for a short moment when the voltage on the collector of 7211 is sensed once every
ms.
Feedback Circuit
The feed back circuit consists of 3101- 3106, 6105 and 7101. When a current flows through the LED of 7101 and
the output pin 4 is high and turns off transistor 7102. Port R61 of the micro processor is normally kept low
(Vss), except for a short moment when the voltage on 2201 is sensed. If 7102 is off the micro processor will
read a ”zero” and when 7202 is on the micro processor will read a ”one”. The RC time constant 2201 * 3201 is
only 5,6 us and will not influence the timing of the feedback signal.
Keyboard
All keyboard switches are connected in a matrix with four rows and four columns. The columns are pulled high,
one at a time, during scanning. The key scanning is combined with the display drive circuitry.
If any key is pressed, one of the processor inputs will be high when the corresponding output is high. The
inputs K00-K03 have internal pull down resistors.
When OTP is used external pull down resistors must be used ( 3285, 3286, 3287 and 3288).
