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So I've made a PWM fan controller based on 555 timer, but it does not acturally modulate any pulses, the output is exactly the same as the input so the fan works but does not react to changes in pot resistance.

The output of 555 timer does not have any pulses either, just a plain 11v DC signal, exactly the same as the input power.

Where should I dig?

Schematics:

enter image description here

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  • \$\begingroup\$ Circuit looks nominal to me. Is C1 charging up? \$\endgroup\$ – Trevor_G Jun 13 '17 at 16:34
  • \$\begingroup\$ hooked up an oscilloscope to it, powered it up and smoke started coming out of the MOSFET, so I guess I'll have to make another one now) At least I'll get a chance to use my new flux paste) \$\endgroup\$ – user1822227 Jun 13 '17 at 20:41
  • \$\begingroup\$ How is the +12V behaving? Is the mosfet switching causing deviations on the +12V line? If so, that could interfere with the 555's operation. While on the subject, the 555 could probably do with a decoupling cap anyway. \$\endgroup\$ – marcelm Sep 1 '17 at 20:38
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The schematic works perfectly in LTspice. I would first double check you built it correctly, if it still dosen't work, I would replace the 555 timer.

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