No matter what I do I cannot get Macromans PWM circuit to work... First off I put it together just using the circuit diagram... hours later of fiddling and resoldering all I could get it to do is run the fan at full speed permanently!! So I binned that one and started again, this time making an exact copy of the circuit in the article, now once again hours later the circuit simply runs the fan at full speed. I ordered all the components from Rapid Electronics using the codes in the article. I have managed to verify that all the components used are the right description/value, apart from C1 ( the capacitor which sets the pulse frequency), in the article it is listed as being a 0.1microfarad cap. the cap. matching Rap El code 10-3220 is 100n value. If my memory serves correctly though micro is *10 to the -6 and nano is *10 to the -9 therefore 100n and 0.1 micro should be the same. Any thoughts would be appreciated, this is driving me crazy
Have you fitted C2 (220uF)? The circuit needs it. You may have a particularly noisey PSU so try a 1uF cap between the wiper of VR1 and GND.
Thanks for the reply. I had included the 220uf cap and have now tried it with a 1uf cap across the VR1 wiper and GND... unfortunately still no joy, the problem remains the same. I have also tried the circuit on my Enermax 350W psu (I beleive the same type as you used in the article) without success. I have rechecked this circuit over and over, i'm sure it is identical to the one in the article.... I've never had this much trouble getting a circuit to work before
Difficult to diagnose the problem without testing the board. Assuming the connections are all correct with no shorts then that would indicate a faulty component. One point - I had a piece of stripboard that caused the same symptoms. Everything I made on it, including this circuit, failed to work properly, strange as it may seem, it turned out to be a faulty board! I scrapped the board and used a different piece with no problems. Just a thought If you connect the wiper to GND does the fan stop?
Thx again I'm just about to rebuild the circuit again.... I connected the wiper to GND and the fan remains on, so I guess somehow I'm managing to bypass VR1...
