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Thread: Low voltage on the 12V rail in a brand new Cx450

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    @ssm002 to measure the voltage at 12 V rail you just need to power on the PC with all the cables connected and take the free PCI-e cable and just put the measurment probes like that: red one at the yellow wire and the black one at the black wire.
    If your PSU have all black cables just take a look at the image in the link below in order to make an idea where and wich cable is the positve (yellow) and wich one is ground (black)
    https://i.stack.imgur.com/M3aeL.png
    Once you do this, the value on the multimeter need to be between 11.4 and 12.6 V wich are the Atx tolerances.
    You just need to touch the probes on the insulated side for more safety.

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    Quote Originally Posted by Al3xand3r View Post
    @ssm002 to measure the voltage at 12 V rail you just need to power on the PC with all the cables connected and take the free PCI-e cable and just put the measurment probes like that: red one at the yellow wire and the black one at the black wire.
    If your PSU have all black cables just take a look at the image in the link below in order to make an idea where and wich cable is the positve (yellow) and wich one is ground (black)
    https://i.stack.imgur.com/M3aeL.png
    Once you do this, the value on the multimeter need to be between 11.4 and 12.6 V wich are the Atx tolerances.
    You just need to touch the probes on the insulated side for more safety.
    Thank you,i will keep that in mind.And yes,the cables are all black and therefore the image that you've posted will come in handy.If by any chance i connect the probes of the multimeter to the wrong wire then could that cause any kind of short circuit or damage something in the mobo or PSU?

    And would it be ok if i tested the molex connector instead?Which connector is likely to give readings that are more consistent with the actual values in the 12v rail?

    I am not sure when i will be able to open up my cabinet and check everything as i am quite busy at the moment-i am guessing it will take a while before i can report back my findings.

    So would it be ok if i ignored the software readings for now and continued to use this psu?What signs of instability/system malfunction can occur if the psu fails to supply proper voltages on its 12V rail?I'd be much obliged if someone could shed some light on this.

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    (EDIT: hmm, from what i saw at CX600 review https://www.techpowerup.com/reviews/.../CX600M/5.html , this series voltage regulation is very mediocre, so there is probably nothing wrong with the PSU, probably these are its normal values!!) .
    Flaw in the reasoning is CX600M is based on different (worse) platform.

    That being said, if DMM shows OK values, and software does not, disregard the software. I don't see the need to be concerned about PSU until specific problem happens.

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    And would it be ok if i tested the molex connector instead?Which connector is likely to give readings that are more consistent with the actual values in the 12v rail?
    Yes, would be more than ok to reading the voltage also at molex connector. In idle should have the same values at the PCI-E and CPU connector. In load instead is possible to have other value like a couple of milivolts higher, like 0.02-0.06 volts, wich is insignifiant, and perfectly normal.

    If you accidentaly make a short between the yellow wire an black, the PSU has a SCP (short circuit protection) and it wold be just turn off an nothing more. With this "occasion" you test the SCP protection also.

    The simpoms of out of spec voltages are random crashes/restarts/blue screens or shutdowns of your computer, wich i think is not the case.
    Anyway, with that values of your HWinfo readings IMO you have a normal and very good voltage between 11.90 and 12.10v.

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    Thanks once again,alexander.And what could happen if i ended up connecting the red and the yellow wire on the molex connector by mistake?Could it also result in any short circuit or other anomalies? :P

    I will definitely test the psu,but not right now as i need to get some work done.I have already spent much of my time in troubleshooting this issue these past 2 days.

    Btw if its really outputting 11.6V under load,could that be considered safe for regular use?

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    Is better to avoid a short between red wire (5v rai) and yellow wire (12v rail) once its connected on the motherboard.

    With 11.6 Volts on 12 rail is fine since the minimum allowed by the ATX standard is 11.4 Volts. But according to my experience with the readings of HWinfo software compared with the multimeter, the voltage of your PSU is more than ok, and is by far closley to 12 V than value reported by the HWinfo.
    I always used HWinfo for monitoring the CPU Vcore, in parallel with other softwares (like CPU-Z, Aida64) an i've seen alot of weird voltage readings. With the same PSU on two different motherboards there was differences in voltages on all rails not only the 12v one.

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    That's good to know! A friend of mine once told me that he had accidentally connected the 5v and the 12v wires of a molex connector to his multimeter while attempting to test his power supply-although it didn't create any discernible problems and both the psu and the computer continued to work normally,he got wrong readings on the multimeter and upon rebooting the computer he discovered that all cmos values had been reset! Even after restoring all settings the cmos values weren't being saved-so as a last recourse he changed the battery of the mobo and then his system started working normally again.

    Does this indicate that by inadvertently connecting the 12v and 5v wires to his multimeter,he may have caused a short somewhere which might have drained the mobo's battery completely,thereby resetting the values in the bios?afaik he too was using a psu from a decent brand,probably Corsair.

    I am asking as it would be quite interesting to know what might happen in case a short circuit occurs and the psu's built in safety measures fail to kick in/activate.

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    Software shows 3V on the 12V rail on one of my old systems here. Just to tip you how absurdly inaccurate such measurements can get, hehe. (The DMM voltage last measured was 11.84 under load, it's a cheap Cooler Master B500 PSU). It's a system I used for F@H, it has an i7 860 and a GTX 980. It's out of service now though.

    Rig 1: Core i5 6600K - Asus Z170 Pro Gaming - Corsair Vengeance 16GB PC2666 RAM - MSI GeForce GTX1070 - Samsung EVO 850 500GB SSD + 2TB Seagate SSHD - Corsair RM550x - Fractal Design R5 - Win10 64

    Rig 2: Ryzen 1700X @ 3.9 GHz - Gigabyte X370 Gaming 5 - Corsair LPX 16GB PC3200 RAM - Gigabyte GeForce 1070 - 250GB Samsung EVO 850 SSD - Corsair RM650i - Win10 64
    HTPC: AMD A6-6400k - MSI FM2-A75IA-E53 mITX - 8GB Kingston HyperX 1866MHz - 3.5TB storage - Silver Power 460W passive - CM Elite 120

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    lol-that seems way off the mark.I dont think the computer would have even booted up if the values were that low.

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    Maybe the motherboard itself (on top of the 24-pin) is causing the drop @ load.

    Hmm an idea for investigation: Does "overclocking" mobos suffer less vdrop compared to cheap mobos.

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