"Urgent Help Needed"

Dear friends,
I am having some problem with the circuit which i am posting below. Its a temperature dependent fan speed control, i am getting a voltage difference of around 8 volts till pin 1 of MOC3011 but then, i am unable to get any voltage difference across the output load(AC fan) and hence i am unable to change the fan speed. Please help me, need to submit the project within 2 days from now.
Please help.
**broken link removed**

If you measured ( voltage difference) voltage from GND to MOC pin1
and get 8V
and circuit is as in drawning,
IC3 and D7 are dead ( at least ).

suhusumu said:

Dear friends,
I am having some problem with the circuit which i am posting below. Its a temperature dependent fan speed control, i am getting a voltage difference of around 8 volts till pin 1 of MOC3011 but then, i am unable to get any voltage difference across the output load(AC fan) and hence i am unable to change the fan speed. Please help me, need to submit the project within 2 days from now.
Please help.
**broken link removed**

Click to expand...

please insure that circuit running dual power supply

i tested D7 and IC3, they are fine. But still the output across the load is not showing remarkable change. Can i use MOC 3021 instead of MOC 3011??
and yes, i am using dual power supply...

That circuit looks complicated for what it does, but that means it'll probably work.
Your readings may not mean much on your meter, pin 1 of the opto triac is pwm modulated, your meter may not respond well to this, some modern dvm's have duty cycle measurement, this would be much better.
Also you reading accross the fan my not mean much, because the fan is phase angle controlled some meters dont read accurately, you'd need a simple filter network to convert the output to a peak voltage to get a meaningfull reading.
A 'scope would be best as you'd be able to see the output waveform switching as the temp on the sensor changed.
Its fair to assume though that the circuit is working as the voltage changes on pin one of the opto, check the trimpot and resistor to see if mains voltage has nuked them, and check you have mt1 and mt2 on the triac the right way round, if that fails remove the opto and triac and test them using a dc power supply (9v battey) an led and a 1k resistor to trigger the opto, and to trigger the triac (both ways round there are 2 trhyristors within).

The schematic part is ok, how do we know that you have constructed well. May be you are missing something? So it will be difficult to tell or help like that. Please show some pictures or video so that we can be sure that the construction is ok.

Please read the subscequent issues of this magazine and you will find the problems with this schematics. I suspect the problem to be near D7 and D8 but I am not sure.

Thankyou

PS: just replace VR3 and R18 with 330ohms 1Watt resistor. If your load is more than 4Amp then you have to use 330Ohms 5Watts. May work!! Also put a 330Ohms 1/4Watt in series with an LED at input of MOC3011 so that you can know if the MOC gets input signal.