Bad news. I replaced the triac and the zener diode, I tested the voltage across the zener, it is 18V. When I turn the unit on the led flashes one time only and the resistive loads don't heat up.. there is no voltage across them. I tested the voltage at the IC output that is connected to the gate by an oscilloscope and found no voltage. So there is a DC voltage on the IC and there is no output voltage. I think the IC is bad. I can't get another IC... I tried to disconnect the sensor but it didn't work too. Disconnecting the sensor means it's resistance is infinite, maybe it's a PTC and not NTC? then what should I do? connect the sensor terminal with COM and try?

 

I tried to disconnect the sensor but it didn't work too. Disconnecting the sensor means it's resistance is infinite, maybe it's a PTC and not NTC? then what should I do? connect the sensor terminal with COM and try?

To find out if it's a PTC/NTC measure resistance from L1 to COM, and heat the sensor up with an hairdryer. The resistance should change.

 

The thermistor (NTC/PTC) is bad. It's crumbled. I prefer to exclude it even if this will shortens the unit's life. The last solution will be connecting the power line from the plug directly to the resistive loads. What is usually used in such applications, an NTC or PTC? If it's an NTC then I can try disconnecting it and trying the unit.. I did that but the unit didn't worked as I previously said. If it's a PTC then I will try shorting both lines to it, i.e. COM with RT.
Lets try our last possible solutions and end this topic.
Regards,
Hazim

 

If it's a PTC then I will try shorting both lines to it, i.e. COM with RT.

You can either short it or try with different resistors to see if anything changes. I'm not a friend of shorting something in unknown circuits.

Did you measure the voltage at the gate of the triac or at the output of the IC? What about the diode / resistor in series, are they ok?

 

But there is no other way to proceed :S. In the worst situation I'll connectd the loads directly as I said, so I'll not care anymore to the board and controlling the temperature.
Yes I measured the voltage at the output of the IC and found no voltage, I told you that in post #21 (in the top of this page). I'll try with resistors and write down what happens.

UPDATE:
I tried resistors from 20k till 100 Ohm and then short circuit.. it didn't work.

Update:
It seems to me that the loads are overheating when connecting them directly to 220V.. I'll not measure the current they drain, I'll connect them directly and end this issue. The resistance will not decrease very much and the calculated power is not that much... Anyway thank you very much, I really appreciate your help

Regards,
Hazim