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Thread: LCD loads of electronic Noise (humming on immage with M4- ATX)

  1. #1
    Variable Bitrate
    Join Date
    May 2010
    Herákleion, Iraklion, Greece, Greece

    LCD loads of electronic Noise (humming on immage with M4- ATX)

    Hi. my current system uses 2 LCDs. one small, powered from the pc PSU,
    and one 15,6 " wich is powered by an inverter .

    up untill now, i was powering the pc with an inverter--> and then normal house PSU. this had resulted in loads of noise in the screen. but only the big one. the small works perfect. i got by it, by cutting the "ground/yellow" cable from thecable that connected the psu with the inverter.

    But now, i have bought a M4 atx power supply. and i jut cant figure how to get read of the noise in the screen. i also use an amplifier, and an external usb sound card. they also had noise, but ground loop isolators solved it.
    i have tried diferent gound points, and no, the signal cables are not on the same side with the power and bla bla..

    i am thinking that maybe it's the alternators fault, cause, when i rev up, there seems to be some difference in the haming of the screen (but small). i also know, from a readings i did to a car sensor, that (on that sensor) there was an AC current of 0,1 v that went to 0.2 the more i reved...

    i', thinking that maybe , cutting the ground wire from the inverter-->LCD would work, but i dont wanna risk using the lcd without ground.

    Also, the PSU/AMP are grounded to the chasis atm, and the lcd inverter is grounded elsewhere, at the battery. (although, grounding it on the same ground when i had the 2 inverters hadent solve anything...) the lcd is connected with 5 meter vga cable...

    this is prety much a shot in the dark, so any advice would be helpfull!

  2. #2
    Variable Bitrate
    Join Date
    May 2010
    Herákleion, Iraklion, Greece, Greece
    so... some extra info:
    1)after all the noise is on both screens.
    2)even if i connect the big LCD to house outlet, (no inverter in system) , the humming is the same..
    3) with car turned off, (no alternator working) , still the same
    4) the speakers, still do some noise some times, even with ground isolators
    5) I have the motherboard chasis grounded as well (same spot as anything else). IF i try to power up with that ground removed, the big screen wont start (it turns off and then off). IF i turn on the pc with ground, screen works with noise..

  3. #3
    Raw Wave
    Join Date
    Nov 2009
    The M4 is a very noisy PSU. MickZ has some wonderful replies re this and the need for coaxial capacitors etc.

    Be very wary about cutting grounds. Shields can be interrupted, but loss of GND can be very damaging to equipment.
    That applies to both power and signal grounds. If you cut the power/signal "return" GND then either the thing won't work, or it may work intermittently as it grounds thru other signal paths, or it blows those alternate signal paths.

    The inverter "GND" that you cut was probably its earth (safety GND) which might connect to its chassis and to its input -ve (GND) 12V supply.
    (Noting that both AC outputs should be isolated from the input and case (for legal and safety reasons), but how any output GND is interconnected to the inverter case or 12V supply (if at all) can vary with application. Normally the AC output GNDs would be tied to the Neutral (not Active) AC line if polarised 3-pin AC connectors are used (as in England & Australia etc) if the typical domestic AC grounding philosophy were used - ie to blow fuses if loads have internal shorts to chassis).

  4. #4
    Constant Bitrate ephect's Avatar
    Join Date
    Jul 2007
    Melbourne, Australia
    im not too familar with your set up, but i would add another ground point from the engine to the chasis, and engine to battery using good quality cable.

    this generally cleans up noises from the alternator.

  5. #5
    Variable Bitrate
    Join Date
    May 2010
    Herákleion, Iraklion, Greece, Greece
    i know the risks about cutting grounds... but i did itonly cause i couldent find anyother way to solve it... Atm i was thinking that maybe i could cut the signal grounds, and ground them as well to the chasis. but this, even if it works, dosent really solve the problem... just hides it.
    I will try the better cables, but i dont know if they will work, cause if it was a problem relating the chasis cables capacity, then the noise would vary depending on what is working and what not...
    The amplifier and the PSU are connected to the same spot, and to the same ground, with same length cables. BUT i noticed that the amplifier has 0.2 volt more on its terminals, than the PSU!! (13.11 and 13.30) ... amplifier has 2 gauge cables, and the PSU has one 2 gauge for ++ and one smaller for ground... and the + has in series a small fuse (not for sound systems, but one from those that the car uses), which might be bottlenecking... but again i dont think it would cause noise...

    could you clear up on coaxial capacitors plz?

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