mac pro 3.1 rear fan not working

[allenlyc]

I have a mac pro 3.1 year 2008. I did an upgrade to 20gb ram and GPU changed to HD 5770.
recently the memory rear fan is not working, ending up the beast shuts down itself due to the heat.
I replaced it with a third party fan, same size and width. Everything is assembled accordingly, however it only spins during boot and it stops after that. Front fans and PSU fan are working perfectly fine, just the memory rear fan is not!
what is the problem?

 

[flyinmac]

I have a mac pro 3.1 year 2008. I did an upgrade to 20gb ram and GPU changed to HD 5770.
recently the memory rear fan is not working, ending up the beast shuts down itself due to the heat.
I replaced it with a third party fan, same size and width. Everything is assembled accordingly, however it only spins during boot and it stops after that. Front fans and PSU fan are working perfectly fine, just the memory rear fan is not!
what is the problem?

Most likely the 3rd party fan isn't talking properly with the Mac Pro logic board.

I'd make sure it's a high rpm fan. Then I'd run some longer power leads up into the DVD drive bays and use a molex power splitter to provide another power connection for the fan. And power the fan from there. That way it will always spin.

Personally I'd probably do it slightly differently. But not knowing your comfort with a soldering iron, I advise the above as a relatively simple method.

Also run a temp monitor program to observe the effectiveness of the fan once you get it working.

Ideally aim for somewhere under 50 degrees Celsius in the memory area. The cooler the better.

 

[666sheep]

This info should be useful. You need to do it in opposite way.
However the best would be to buy used fan on eBay, Craigslist or so.

 

[allenlyc]

hey,
both your comments make a lot of sense!
at least to give me brainwave of what I should do next since this issue has been daggling for weeks!!!I will try tonight and come back!

 

[flyinmac]

hey,
both your comments make a lot of sense!
at least to give me brainwave of what I should do next since this issue has been daggling for weeks!!!I will try tonight and come back!

Let us know how things work out for you.

The old Mac Pro's are good machines. And deserve a long life. Hope you're able to keep it in service.

 

[allenlyc]

Let us know how things work out for you.

The old Mac Pro's are good machines. And deserve a long life. Hope you're able to keep it in service.

it is indeed a beast,a monster.this is what i found.both fans have the same dc12v but different amp,0.75a vs 1.5a.this could be the cause.Still,following the approach to draw the current direct from the molex is it going to work or not?

 

[flyinmac]

it is indeed a beast,a monster.this is what i found.both fans have the same dc12v but different amp,0.75a vs 1.5a.this could be the cause.Still,following the approach to draw the current direct from the molex is it going to work or not?

Yes, drawing power from the molex will work. Use a splitter so you aren't hacking into the factory wires. And also makes is undoable in the future if needed.

On regular molex splitters, the yellow is 12v and red is 5v. Black is ground.

If fan says it's 12 volt, then run on 12v for highest speed. If you connect it to 5v it will spin slower.

 

[CapnDavey]

My fiend Guy had the same issue with his 3,1 he took the fan out spun it by hand it was tight he put it back in and it worked try that!

 

[allenlyc]

hey guys
sorry to update the post late...ordered the molex and it took 2 days to reach.
It works finally! though not from the rear fan connector but from the PSU via 2 different molex connectors.
thanks guy for your input
[doublepost=1474645070][/doublepost]given a photo,this is what i have done.

 

[flyinmac]

Glad it's working. Always happy to help.

If you're looking for a cleaner routing path, you can snake the wires through a hole near the front of the machine in the DVD compartment. There's a cable pass through area there.

It'll come out about where the front case fans are. Then run it under the housing for the memory modules.

Just watch for heat sources. Like don't rest the wires against a heat sink.

Glad it's working for you. Always happy to help.

 

[OS6-OSX]

If you're looking for a cleaner routing path, you can snake the wires through a hole near the front of the machine in the DVD compartment. There's a cable pass through area there.

It'll come out about where the front case fans are. Then run it under the housing for the memory modules.

Just watch for heat sources. Like don't rest the wires against a heat sink.

I just gave my 3,1 it's 6 months cleaning. You can see the areas flyinmac is speaking of.