Burnt out fans - fixable?

[Orijin16]

I decided to reduce the voltage on 2x ek vardar F4's and 2x Coolermaster generic high static pressure fans, from 12v down to 7v while maintaining PWM control.

To do this I butchered a 4pin molex connector so that the fans ground wire went to 5v and the 12v to 12v, with all 4 PWM wires connected to a single motherboard header along with the RPM wire from one of the Vardars.

Unfortunately, because I was tired and being harassed by my children what I actually did ws wire the fans ground to molex 12v and the 12v to molex 5v, needless to say there was a strong smell of burning and none of the fans span up.

The coolermasters actually survived the ordeal and are now happily wired up at the reduced 7v, along with a spare vardar F4, but my other 2 are dead (tested individually with original wiring).

Is there any way to fix them? My Alphacool Monsta is missing his push-pull buddies but I'd rather not shell out another £30 for more if I can rescue the old ones.

 

[Ferrum Master]

Ek vardars died? The controller is dead = new fan. Here take a look to the board. They are all the same, just different resistor setup for RPM settings.

 

[Orijin16]

I'm not entirely sure I understand what you mean, I'm not very electrically minded.

Do you mean the PWM controller is dead? If that's the case wouldn't the fans still spin but without any control?

Or do you mean the motor is dead?

Incidentally, what voltage was actually going to the fans? It's my understanding that wiring the fans ground wire to a voltage reduces the voltage by that amount, so wouldn't it of been getting -7? (5v-12v)?

Sorry if these are incredibly stupid questions, I know how to reduce the voltage but I have very little understanding of the science behind it.

 

[Ferrum Master]

It ain't a brush motor. The step controller coupled with HAL sensor drives the coils. PWM is just an aditional feedback feature of the IC. As you see in the image there is only one integrated power part. And most probably yours has a hole in it.

Anyway if you say you ain't the brightest at electrinics, you have no other choice... order a new one. These things are cheap anyway.

 

[Orijin16]

Ah yes I get what you mean now, I was thinking of it like a brush motor (I used to repair washing machines so was thinking they were similar).

I kinda figured I would need to just buy new ones but had hoped I could maybe do something without having to pay any money, I'm a cheapskate like that lol!

Thanks for the help.