MDD main fan

[Harryoldboy]

Simply, the main fan wont work after changing dead power supply. What have I missed?

Reset PMU after changing battery - Nope.
Changed fan (twice) - Nope,
Changed CPU (thermistor) & paste - Nope.
Swapped logic Board - Nope
Even swapped in another PSU - Nope

Everything ('cept fan)works fine in Tiger or Leopard. Temp just runs up way high till (if I let it) the thermal cut-out operates. Red light OK on logic board. Have I missed something?

MDD 1.42Ghz (alt CPU 1.25Ghz) dual 2Gb RAM

 

[bunnspecial]

Are you sure the fan itself works? As I recall it only has two leads on it and is probably either 5V or 12V(I'd guess the latter). Hook it up to a power supply and see if it spins.

 

[Harryoldboy]

Been there done that

Correct, 2 leads and it's both 5v and 12v for idle speed and full speed. The fan spins up very well under a 12v transformer.

However you are right again in that buying secondhand you can never be certain things function correctly in all regards - but with these machines we have little choice. So if there are means to test, such as you suggest for the fan, it's worth a check-out.

 

[bunnspecial]

Okay, with that out of the way, here's maybe a long shot but something else to check:

The fan connector is something of a stress point on the MDD logic board, and I've seen many bent and/or twisted from folks(myself included) trying to remove a fan, logic board, or PSU without disconnecting the connector first.

You might check the solder joints where the connector attaches to the logic board, and make sure you don't have a fractured solder joint or other obvious problem there.

 

[archtopshop]

If the fan works using an outside power source, then the next thing to check would be the connector. Easiest way would be with a multimeter. Could be a cracked solder joint, as was already suggested.

Also, on my Dual 1.25 FW800 MDD, there is an extra fan connector next to the cpu heatsink. I've used it to test fans before. If I recall correctly, it's voltage rises with the temperature of the cpu, so if your wire will reach it, try plugging into it.

 

[bunnspecial]

If the fan works using an outside power source, then the next thing to check would be the connector. Easiest way would be with a multimeter. Could be a cracked solder joint, as was already suggested.

Also, on my Dual 1.25 FW800 MDD, there is an extra fan connector next to the cpu heatsink. I've used it to test fans before. If I recall correctly, it's voltage rises with the temperature of the cpu, so if your wire will reach it, try plugging into it.

I don't have an MDD near me at the moment so am working on memory, but isn't that the connector where the small fan in the case door is supposed to plug in?

(I also only have a limited amount of experience with the FW800 model, as the only one I have doesn't work currently).

 

[archtopshop]

I don't have an MDD near me at the moment so am working on memory, but isn't that the connector where the small fan in the case door is supposed to plug in?

(I also only have a limited amount of experience with the FW800 model, as the only one I have doesn't work currently).

No, the one I'm referring to is located near the heatsink for the cpu daughtercard. It's not used, but does work because I've tried it. Here's a portion of a photo I found online. The connector in the photo looks to have a little red dot on it.

The fan wire is long enough to reach. If I get a chance tomorrow, I'll give it a try with mine.

EDIT: I tried the "spare" fan connector on my MDD and it functions the same as the one to which the main fan is usually connected. The fan increases in rpm with the rise in temperature. With mine, the speed starts to increase at about 134F. So, if the OP has this "spare" connector on his logicboard, it would be a good place to try to solve his problem. I have included a photo of my machine with the wire connected to the extra connector. The wire just barely reaches.

 

[Harryoldboy]

Thanks Guys

Thanks All. I'll check on the soldering/continuity, good point.

Mine's a bog standard FW400 MDD dual. It hasn't got this extra fan connector. However "her-indoors" has commanded all my repairs MUST be stowed for Christmas and that's this machine, a 7100 and a 7600. So no more fun tinkering till 28th.

Interestingly the thermal cut out operates at 62c (143f) with the 1.25 dual but waits till almost 80c (175f) - if I inadvertently let it - with the 1.42 dual.

 

[archtopshop]

Thanks All. I'll check on the soldering/continuity, good point.

Mine's a bog standard FW400 MDD dual. It hasn't got this extra fan connector. However "her-indoors" has commanded all my repairs MUST be stowed for Christmas and that's this machine, a 7100 and a 7600. So no more fun tinkering till 28th.

Interestingly the thermal cut out operates at 62c (143f) with the 1.25 dual but waits till almost 80c (175f) - if I inadvertently let it - with the 1.42 dual.