Help solving a no POST issue on new build - logic says SYSFAN on Mobo, PSU.Molex or case fans issue?????

Hi, experts, and thanks in advance. I am a rookie builder who assembled my new system in a Fractal Design 305 Node case yesterday and optimistically pressed power button on case to fire it up and... UGH!!! I got a single, momentary blink only on front LED plus a tiny part of a single (1/10) turn on PSU and the 3 case fans then... nothing - no lights, no movement, just dead. So... I checked and rechecked (they were OK all along) but still removed and then re-connected all mobo connections and tried again... same result.

I wondered if there may be a short in mobo/case set up and I decided to remove mobo and start again (outside case this time) and, based on reading online suggestions I also removed, cleaned and re-installed CPU cooler on mobo and reconnected everything... same result :(

I then took everything off mobo and began adding things one by one. By a process of elimination I finally figured out that system would POST and let me get into BIOS, successfully read and identify SSD and HDD, load windows, access web, etc. but ONLY when SYSFAN on mobo was not actively connected to case fans! Everything even worked with SYSFAN plugged in to Molex cable IF it wasn't connected to power supply... but it would not do ANYTHING but blink the LED and then nothing when the case fans were connected to SYSFAN, via either of the two different supplied Molex cables in any of the 3 open PSU slots. (I WAS able to boot PC using ANY of the 4 slots on PSU to connect 12V CPU fan supply on mobo as a means of checking those 3 open SYSFAN PSU outputs.)

After all this testing, I surmised that it could only mean that, either: 1) mobo SYSFAN is somehow bad - manifesting itself when power from PSU comes into it, whether or not case fans are also plugged into it, or, 2) molex cable connection from fan controller to MOLEX is bad/shorting, causing mobo to not POST or 3) Case fans may be incompatible with mobo... either drawing too much on start-up, or something.

I have opened trouble tickets with fractal Designs in case it is a case fan problem (short or mis-wire, perhaps?) and I have also initiated a repair ticket at Gigabyte tech support, too, in case it is a mobo issue.

In the meantime, however, I fear that there is probably something simple I have missed which you bright folks could help me with!?!

FYI: Case fans are single 140mm fractal design at front and twin 90mm fans at rear. PSU is brand new Rosewill Hive 750W 80+ Bronze - which should have AMPLE headroom for these 3 plus the CPU fan, which is ZANTEC Quiet low profile fan. CPU is Haswell 5 series 4670, no graphics card in system at this stage so that is not a factor. Mobo is Gigabyte Z87N-WIFI. Any ideas as to how I should proceed next, tech friends???

3 answers Last reply Best Answer
More about solving post issue build logic sysfan mobo psu molex case fans issue
  1. Best answer
    If I understand your explanation correctly, it sounds like a defective MB. Not all that unusual, it happens. I've had my share. If you still can, RMA it for a new one.
  2. clutchc said:
    If I understand your explanation correctly, it sounds like a defective MB. Not all that unusual, it happens. I've had my share. If you still can, RMA it for a new one.

    Thanks, ClutchC - I hope Gigabyte customer service/repair request I submitted will help me get to bottom of this or get new mobo for my build. I appreciate you taking the time t respond!
  3. Have you tried RMA'ing it to the retailer first? If it isn't too late.
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