Compaq Case/Processor Fan

[AndyM]

My daughter's Compaq stopped booting and stayed stuck on a screen with the Compaq logo and a message: Fan not present, operation halted.
The CPU has a large heatsink with a shroud that conducts air to a 12 Volt case mounted fan. That fan was not operating. I had to use the connector from that fan and splice it to another case fan, because there are four pin positions, with one missing, on the compaq mobo for the fan hookup. Other mobos have 3 pins side by side. New fan does not work. I tested voltage at mobo pins: white=5v, red=7v, black=nil. Are voltages additive, ie: 5+7=12? I don't know if new fan is bad, connectors are bad, or if mobo is bad. Any advice? Thanks.

[bailey]

remove the schroud to get to the fan, blow all the dust out of the cpu heatsink fins, replace the fan after a good cleanning of the entire area inside the schroud,
replace everything back and boot up, it should work fine

[mike breck]

Is the 12V fan a completely new one or was it an existing Compaq case fan? Try changing the connector back or using a Y splitter cable to ensure the 12V fan is working.

You should be able to connect the 12V fan directly to the PSU but, from what you say, you will need to connect the RPM sensor wire to the mobo header before the system powers up.

If it doesn't detect the fan via the sensor wire, then apparently it won't power up.

You can get Y splitter cables with a sensor wire. That enables you to connect the CPU fan to the PSU and then connect the sensor wire from the splitter cable to the mobo header.

Most 12V fans will run at 7V, so that shouldn't be a problem.

Are you sure all your connections are tight and the connector is wired properly?

[AndyM]

Existing fan from another case. Same size, with 12V on the label, which is what the defective compaq fan was marked (12V). I used telephone wire splice connectors to hook up the new switch. I will test them some more and let you know. Which do you suppose is sensor: white, red or black?

[bailey]

white wire is the sensor

[AndyM]

Hey Mike, followed your advice and found a way to test right at the fan motor housing and, sure enough, red wire was dead at new fan. Replaced connector and got it going. Now if it lasts.....Thanks for the replies Mike and Bailey.