Important advance warning before starting the repair.
All electronic and heating parts of the toaster are under high voltage of 230V!!
The toaster is electronically controlled with specially developed IC A0201D.
This ic corresponds to the PT8A2511 Toaster Controller.
– Defrost mode for frozen bread
– Reheat mode
– Operating voltage 3.5 – 5.5
Operation is based on counter comparison. Because the counter comparator is fixed, changing the frequency of the oscillator will also change the switch-on time.
The oscillator is built around C3, C5, resistor R6, the thermistor TH2 and the trim pot RV1. RV1 changes the frequency. This can be set on the outside of the toaster.
The power supply for the electronics is tapped from one of the heating elements and produces approximately 12 V alternating current. This is rectified by diode D1. A simple load resistor R5 ensures that the zener of 5.1 volts can do its job. The IC is thus supplied with 5.1 volts.
As soon as the toaster is switched on, the holding magnet is energized and hold down the switch. By connecting the base of Q1 to ground, the magnet switches off (early) and so the 12 v power to.
When the voltage is switched on by pulling down the tooster, the oscillator and also the comparator start. When the comparison is reached the toaster switches off.
What was the problem?
After investigation, it turned out that the holding magnet was not being held. The tor Q1 received no steering at its base.
Also it turned out that resistor RV1 was defect. That means the oscillator did not start and therefore the whole circuit. The second problem was that the value of the resistor could not be traced. It should be somewhere in the range of 500 K ohms but it wasn’t certain. As replacement, a resistor of 250 Kohm was chosen, which created sufficient time control for correct toosted bread.