Quadra 605 - J13 fan connector

[egrath]

Hi,

i intend to replace the stock fan of my Quadra 605 with a more silent one (Gelid Silent 6, 60x60x15 mm). The connector used to power the fan is J13 on the logic board and has three pins, but only two of them are connected and they are +12V (topmost pin, next to the silk screening J13) and GND (middle pin).

Does anyone knows what the third pin is intended for? On current 3-pin fan connectors the third pin is the tachometer signal, but i doubt that Apple had this in mind back then.

With kind regards,
Egon

 

[egrath]

After doing a little more research on the topic by reading through the technical reference manual, i highly assume that the third pin on J13 is used as an assertion to increase the fan speed (/FANSPEED, Pin 31 on the PDS). As the signal is active high and regular 3 pin fans report their speed on this pin as a voltage ramp, i didn't connected this pin to prevent any unpredictable results and/or damages.

Btw. the original fan also hadn't connected this signal so it's presumably never used anyways.

 

[ymk]

It's used by expansion cards to increase fan speed for additional cooling.

 

[jasonfeinberg]

Hi,

i intend to replace the stock fan of my Quadra 605 with a more silent one (Gelid Silent 6, 60x60x15 mm). The connector used to power the fan is J13 on the logic board and has three pins, but only two of them are connected and they are +12V (topmost pin, next to the silk screening J13) and GND (middle pin).

Does anyone knows what the third pin is intended for? On current 3-pin fan connectors the third pin is the tachometer signal, but i doubt that Apple had this in mind back then.

With kind regards,
Egon

Hi Egon, did you go through with this? I just acquired a Quadra 605 and am trying to get it in tip-top shape, the fan is a bit loud and dirty and seems well-spun, would like to get a new one but want to ensure it fits, connects properly to power, and won't cause any compatibility issues.... thanks!

 

[Bolle]

The way the fanspeed signal works is simple. Normally the fan is connected right to 12V on the positive side. The negative side of the fan is connected to the fanspeed pin on the PDS as well as a resistor that goes to ground. This will run the fan at a throttled speed because all current will go through the resistor.
A PDS card will have the fanspeed pin connected to ground which once the card is inserted bypasses the resistor on the logicboard that’s sitting in the path of the fans ground, resulting in the fan spinning at its maximum speed.