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Registered Member #188
Joined: Thu Feb 16 2006, 05:18PM
Location:
Posts: 67
Just cleaned out a pc fan and as soon as i connected it to a power supply, ma radio began to produce lots of noise. I suspected the Power supply but it wasnt since this setup produced these results: Current Voltage
Now whats that? I know that isnt how its supposed to be like...
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
I think the fan must have an electrolytic decoupling cap inside that has gone bad. Otherwise, I guess it's badly designed or has a manufacturing fault. Nice test equipment, BTW!
Registered Member #188
Joined: Thu Feb 16 2006, 05:18PM
Location:
Posts: 67
Theres no filter capacitor of any sort. The pc board of the fan contains one 4-pin hall switch, one transistor and 4 or 5 smd resistors, thats all.
40Mhz is a little low for parasitic oscillations but if the wires (maybe the wire to the switch) act as capacitors that could be enough capacitance for that freq. range. Still, the fan really shouldnt do that since it causes bad interference.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
I wouldn't be surprised if the circuit needed a capacitor, but they left it out to save space or money. Try looking up the datasheet for the fan driver IC to see if it recommends a bypass cap.
I've never seen a zener oscillate when cooked. They just blow short circuit.
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What the *beep*? PC fan that generates significant HF emissions?
