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Thread: suddenly interferences on audio&video output

  1. #1
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    suddenly interferences on audio&video output

    Hi guys,
    last friday i took up my carpc to fix some vibrating parts inside and to upload some new movies (wireless connection is too slow for this...). No hardware modifications, just some foam to dump some wires that vibrated when the engine was engaged.
    Yesterday I put it in the car and I have noticed immediately poor image quality on the LCD screen, with composite video output. And I heard some noise from the speakers when the PC was on, especially when moving mouse and the hard disk loading. The picture seemed a TV not tuned well, I could attach a photo if you need.
    I tried to rearrange the connected cables but the problem went worse.
    This never happened before. Please notice that the metal case isn't grounded but it's under the passenger seat and it should be in contact with its metal structure.

    I have read it could be a ground loop problem but I wonder why it didn't come up from the beginning. PLEASE HELP!
    -NicGalla-
    custom-made aluminum case | MK2.8+ PSU | EPIA 800 | 256 Mb DDR | 120 Gb 7.2k WD | Wireless Chieftec mouse & keyb | Trust USB Keypad & USB webcam | Majestic TFT 7" 16:9 | WinXP & ME2 | connected to factory head-unit in a PT Cruiser 2.0L

  2. #2
    Newbie Chosen1's Avatar
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    I'd definitely look at grounding first. But since this came up after moving the wires around, it may be this: Do you have any wires inside the case that carry audio? Like and extension wire that gives audio to jacks on the front of the case or something like that? The reason I'm asking is because in car audio it's a big no-no to bundle power wires with audio wires. You're guaranteed noise that way. I've run power wire down the passenger's side, audio down the driver's side, and pc stuff (usb, led's, switches) down the center. I have ZERO noise. And I haven't grounded my case separately (yet). Point is, if you bundled some 12v with some audio, you'll likely increase your unwanted noise. Try to separate those if you can. If they must cross each other, do it at 90, like a "+". Also, ground the case. Between both of those, you should be good to go. Hope this helps.

    -Chosen1

  3. #3
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    Hi Chosen,
    thank you for your reply.
    Both audio and video connections are made directly the the EPIA motherboard. All the wires are run down the centre, because the deck between the two seats proved to be a simple way to hide wires under it. The EPIA motherboard has been mounted with four screws on the case, which should provide grounding because I have used aluminum for builiding it.
    So I'll try to ground the case, maybe before it was installed in a way that grounded itself.
    This problem makes me puzzled, I have installed the system on last summer and never had these interferences until yesterday...


    Nic
    -NicGalla-
    custom-made aluminum case | MK2.8+ PSU | EPIA 800 | 256 Mb DDR | 120 Gb 7.2k WD | Wireless Chieftec mouse & keyb | Trust USB Keypad & USB webcam | Majestic TFT 7" 16:9 | WinXP & ME2 | connected to factory head-unit in a PT Cruiser 2.0L

  4. #4
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    I'm desperate,
    I have undoed all the hw/sw operations I made before getting the interferences, checked cabling and grounding the hard drive, which was electrically isolated from the case because of the suspension rubber. also checked the battery voltage is good (12.2V),
    I heard noise and see interference in the picture when the hard drive is loading or mouse is moving. Considering that separating the power cable from others is the last resort, what can I check?
    Could an ide cable not connected to a peripheral make the interference?
    I have some ferrite cores, could they help the problem?
    Is there a spot to ground the EPIA motherboard?

    Note that the PC when tried at home, using CRT monitor and a AC-DC transformer works well

    This thing makes me so sad, the system worked so well for months...
    -NicGalla-
    custom-made aluminum case | MK2.8+ PSU | EPIA 800 | 256 Mb DDR | 120 Gb 7.2k WD | Wireless Chieftec mouse & keyb | Trust USB Keypad & USB webcam | Majestic TFT 7" 16:9 | WinXP & ME2 | connected to factory head-unit in a PT Cruiser 2.0L

  5. #5
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    I tried to ground all the internal parts, the video interference now has gone (there's still some but the power is not regulated) but the audio buzz is still there. I have read tons of posts in these forum about ground loop but someone says to group the grounds in one point, others say to separate them.
    My system has only three parts: the PC, the LCD display and the factory head unit. Is it right to run a ground wire from the PC to the metal casing of the head unit?

    Thank you for the patience
    -NicGalla-
    custom-made aluminum case | MK2.8+ PSU | EPIA 800 | 256 Mb DDR | 120 Gb 7.2k WD | Wireless Chieftec mouse & keyb | Trust USB Keypad & USB webcam | Majestic TFT 7" 16:9 | WinXP & ME2 | connected to factory head-unit in a PT Cruiser 2.0L

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