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I have a Lenovo p620 machine and I'm trying to swap out the terribly loud fans with Noctua PWM fans. The problem is the 2 chassis fans are using a weird 4-pin connector where the ridges are on the far sides.

See pictures. What are these called and is there an adapter to convert them to regular PWM or even regular 3-pin voltage controlled Noctua fans?

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Chris Smith
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  • The pinout appears to be the same, so... Maybe just a sharp knife? – Jonathan S. Dec 11 '22 at 23:15
  • @JonathanS. Would the risk be breaking the PWM fan or the motherboard if I clip the ridge and plug it in? I'm fine if it breaks the fan - but replacing the motherboard would be expensive. – Chris Smith Dec 11 '22 at 23:18
  • There won't be any risk as long as the ridge is removed cleanly. Just don't plug it in until it's all cut off properly. Worst thing that could happen is that you ruin the plug on the fan cable if you cut too deep, for example. But do measure the voltage on the connector first, as suggested in Tom Carpenter's answer. – Jonathan S. Dec 11 '22 at 23:29
  • Well, and be careful you're lining up the connector correctly. You lose some indexing when you cut off that "misplaced" ridge. – TimWescott Dec 12 '22 at 01:59
  • The idea with the keying is likely to prevent the assembly worker at the factory from accidentally mis-connecting the various fans. Also note the connector color difference with DIMM_FAN2. This is often referred to by the Japanese term [poka-yoke](https://en.wikipedia.org/wiki/Poka-yoke). – user71659 Dec 12 '22 at 23:41
  • swap the connector shell ... look at the other side of the connector ... there may be holes for operating the contact latch tabs – jsotola Feb 28 '23 at 16:36

1 Answers1

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Looks like they've just used a regular Molex 4-pin KK connector. This is as opposed to the standard fan connector which is a modified version with alignment pin designed to allow both 3-pin and 4-pin fans. I guess they didn't want anyone to be able to connect 3-pin fans to it, as to why, who knows.

While it is just a guess, it appears they've used the standard pinout. You could test this by measuring the voltage between the yellow and black wires. It should be +12V on yellow relative to GND on black.

Beyond that, the PWM/Tacho pin should be pretty low risk of damage if they are not right - the output of the fan is open drain with no pull-up, so can only pull to ground. The PWM input to the fan should also be high-z with no pull-up, so should cause no damage.

If you feel happy enough the pinout is correct, one option is you could modify the connector on your new fan with a knife or some snippers (just remove the alignment tab that's in the way.).

Alternatively, it's relatively easy with a tiny jewlers screwdriver or other thing flat object to press into the little holes on the back side of the connector and gently pull the wires out. In which case you could transfer the housing from the old fan onto the new one, or buy a new housing (Molex 22-01-3047 or equivalent). Personally I'd just cut the inner alignment tab off.

Tom Carpenter
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    I redid the fans in a supermicro server and carefully trimming the one extra tab of plastic worked fine. The clip is still there to stop things falling off with vibration. You just need to take care to not have an off-by-one error when connecting. – Criggie Dec 12 '22 at 19:22
  • Thank you so much @Tom Carpenter. I asked this question on reddit, linus tech tips and other places with no answers. Unfortunately I don't have a multimeter, but as you suggested (and others) I'm going to clip a ridge off a Noctua PWM fan and plug it in and see what happens. Will report back with results. – Chris Smith Dec 12 '22 at 23:35
  • @ChrisSmith If you often do DIY jobs in your house, I advise you to buy a bottom-of-the-range multimeter (you can get a decent one for about 50$). If you really don't want to spend that much, a crappy el-cheapo multimeter can cost you as little as 10$. This latter kind is more than enough for low-voltage and/or low-energy circuit work (such as your fan), but don't use them for mains or power-supply: they lack lots of internal protection circuitry and you may risk your life even if they are "rated" for mains or 1000Vdc. – LorenzoDonati4Ukraine-OnStrike Dec 13 '22 at 11:26
  • Well it seems to be working though the Noctua 92mm fans actually run louder under load than the stock/OEM fans - ha. I also put 80mm Noctua fans on the CPU cooler, which does use regular PWM headers and they also run much louder than the stock fans, though the temps are 5c lower. I might try another brand of fan but so far the whole idea has been a bust :( – Chris Smith Dec 15 '22 at 16:52