My old Pentium III Computer was in halt for three months. The Fan cable of the processor (SL35D , P3-450Mhz Slot) had got damaged after being cut by the fan blade itself. I searched in every possible computer shop of Kathmandu for the replacement of the fan cable or the fan itself. All was in vain. Instead I lost my damaged fan cable. I found that the Pentium III generation parts were already outdated in the market, plus I came to know that the fan always came attached with the CPU, in case of P3-450Mhz. So the only option from the market was to buy a new P3, that also, only if I get lucky. So I opted to repair it myself.
Figure 1a shows the P3 processor I had.
Figure 1a) SL35D , P3-450Mhz
After going through many repair shop, I finally managed to get a fan cable that had only one head as shown below in figure 1b:
After going through many repair shop, I finally managed to get a fan cable that had only one head as shown below in figure 1b:
Figure 1b) Fan cable
The coloring scheme of the computer wires tells that yellow color wire is of 12V and the black color wire is 0V ground. But what the green wire was for? I fixed the cable head into the motherboard (of course without CPU) and turned on the SMTP power supply. On measuring the voltages of the fan cable wires using voltmeter, I found that to be true. The yellow wire was at 12V and Black wire was art 0V. But the green was at 10.2 V.
Then I had to investigate what each of those three pin on the fan of the P3 were. I googled for nearly two hours and finally got onto the Intel’s “Hardware Design Site Archives” located at http://www.intel.com/design/archives/processors/pentiumiii/index.htm . On that page, the article “SC242 Connector Design Guidelines” drew my attention, as processor had SC242 packaging and I had to know about the electrical connecter of the fan. Then in the 24445209.pdf file that followed, I was able to electrical connector diagram as shown in figure 1c.
Then I had to investigate what each of those three pin on the fan of the P3 were. I googled for nearly two hours and finally got onto the Intel’s “Hardware Design Site Archives” located at http://www.intel.com/design/archives/processors/pentiumiii/index.htm . On that page, the article “SC242 Connector Design Guidelines” drew my attention, as processor had SC242 packaging and I had to know about the electrical connecter of the fan. Then in the 24445209.pdf file that followed, I was able to electrical connector diagram as shown in figure 1c.
Figure 1c: Fan cable connector descriptor, extracted from the Intel site
On looking the cable (I had, figure 1b) and the above diagram, their description matched. The pin no. 1 had black wire with 0V (GND). The pin no. 2 had yellow wire with 12V. So I was certain that the third green wire must be for sensing the fan speed.
After figuring out what those three wires were for, I still had to figure out which pin was for what. The article from the Intel told that “Baseboards must provide a matched power header to support the boxed processor”. So the middle pin of the CPU fan must be for 12V. Now I had to figure out which was for ground GND and which was for SENSE. For that I set my voltmeter to measure the top pin and the middle pin and blew the mouthful of air into the fan. As the fan revolved I detected some voltage upto 400 mV. So this top pin must be the ground. When I measured the voltage across the middle pin the bottom pin, there was no significant voltage. Also the Intel’s article tells that the SENSE pin gives two pulses per fan revolution and was an open collector output. That is why it may not have given any voltage. Since the motherboard must have used pull up for this SENSE pin, the 10.2 V was observed at the motherboard side.
So after figuring out the pins of the CPU, I solder them accordingly as shown in figure 1d below:
On looking the cable (I had, figure 1b) and the above diagram, their description matched. The pin no. 1 had black wire with 0V (GND). The pin no. 2 had yellow wire with 12V. So I was certain that the third green wire must be for sensing the fan speed.
After figuring out what those three wires were for, I still had to figure out which pin was for what. The article from the Intel told that “Baseboards must provide a matched power header to support the boxed processor”. So the middle pin of the CPU fan must be for 12V. Now I had to figure out which was for ground GND and which was for SENSE. For that I set my voltmeter to measure the top pin and the middle pin and blew the mouthful of air into the fan. As the fan revolved I detected some voltage upto 400 mV. So this top pin must be the ground. When I measured the voltage across the middle pin the bottom pin, there was no significant voltage. Also the Intel’s article tells that the SENSE pin gives two pulses per fan revolution and was an open collector output. That is why it may not have given any voltage. Since the motherboard must have used pull up for this SENSE pin, the 10.2 V was observed at the motherboard side.
So after figuring out the pins of the CPU, I solder them accordingly as shown in figure 1d below:
Figure 1d) Heat sink fan soldered with the fan cable.
The pin 1 (from motherboard) with black wire (0V) was soldered to top pin; pin 2 with yellow wire (12V) was soldered to middle pin and the pin 3 with green wire (10.2 V) was soldered to the bottom pin. Then I insulated those soldered area using insulating tape.
One doubt I had was that when I applied 12V across the top and the middle pin of the fan, it did not rotate. Normally in my opinion it should have rotated.
Next I fitted the whole CPU and the fan into my machine and started it. Guess what happened!
It did not work. The fan still does not rotate.
(So this article is still incomplete, and next time I am going to directly operate into the internals of the fan. The fan should have worked fine as far as I have known. May be there is some thing wrong in the coil or the circuit of the fan. If I have made any mistake in my reasoning, please feel free to comment on it.)
(Please do the above steps at your own risk.)
References:
“Hardware Design Site Archives”, 24445209.pdf from http://www.intel.com/design/pentiumii/applnots/243397.htm
The pin 1 (from motherboard) with black wire (0V) was soldered to top pin; pin 2 with yellow wire (12V) was soldered to middle pin and the pin 3 with green wire (10.2 V) was soldered to the bottom pin. Then I insulated those soldered area using insulating tape.
One doubt I had was that when I applied 12V across the top and the middle pin of the fan, it did not rotate. Normally in my opinion it should have rotated.
Next I fitted the whole CPU and the fan into my machine and started it. Guess what happened!
It did not work. The fan still does not rotate.
(So this article is still incomplete, and next time I am going to directly operate into the internals of the fan. The fan should have worked fine as far as I have known. May be there is some thing wrong in the coil or the circuit of the fan. If I have made any mistake in my reasoning, please feel free to comment on it.)
(Please do the above steps at your own risk.)
References:
“Hardware Design Site Archives”, 24445209.pdf from http://www.intel.com/design/pentiumii/applnots/243397.htm
1 comment:
For anyone finding this old post.. The pin out posted is only for the motherboard connector, not the CPU. The correct order for the CPU from the top is: fan speed, ground, +12V
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