Screen becomes blurry after plugging hard drive


17 posts
by jjggag » Fri Nov 02, 2012 10:52 pm
Scenario:
Raspberry model B powered by 1A usb.
Hard drive: 2TB WD20Ears 3.5'' so I use this adaptor from sata to usb: http://dx.com/p/usb-2-0-to-sata-ide-5-component-cable-black-10113?item=8 so it's self powered.
The hd is connected to a Powered usb hub: 'Newlink NLUSB2-222P 4 port USB 2.0 Hub with 5V 2A PSU'.
Only for the record: that usb hub is in this list: http://elinux.org/RPi_VerifiedPeripherals
OS: Raspbmc.
Actually everything works fine, the hd is automatically mounted, xbmc detects it etc.
However right after I plug the hd in the hub (or directly to the raspberry, or even if I reboot with the hd already plugged in) the screen becomes blurry, with snow/noise..
Do I need a better usb hub providing more Amps? even when the hd is self powered? Or what do you think is the problem? Thank you very much in advance.
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by aaa801 » Sat Nov 03, 2012 12:21 am
Is your powered hub backpowering?
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by johnbeetem » Sat Nov 03, 2012 4:24 am
Take a look at this entry at the RasPi Troubleshooting Wiki: http://elinux.org/R-Pi_Troubleshooting# ... VI_monitor

I have this happen when my TP1-TP2 voltage drops below 4.65V. If you have a volt/multimeter, check TP1-TP2: it should be at least 4.75V for reliable operation.

You may be able to fix the problem by editing the config.txt file to set config_hdmi_boost=4, as suggested by the Wiki.
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by jjggag » Sat Nov 03, 2012 11:38 am
aaa801 wrote:Is your powered hub backpowering?

According to https://www.modmypi.com/shop/raspberry-pi-accessories/New-Link-4-Port-USB-Hub-(USB-2.0-with-Mains-Adaptor) is not.
johnbeetem wrote:Take a look at this entry at the RasPi Troubleshooting Wiki: http://elinux.org/R-Pi_Troubleshooting# ... VI_monitor

I have this happen when my TP1-TP2 voltage drops below 4.65V. If you have a volt/multimeter, check TP1-TP2: it should be at least 4.75V for reliable operation.

You may be able to fix the problem by editing the config.txt file to set config_hdmi_boost=4, as suggested by the Wiki.

I forgot to mention that I'm not using HDMI but Composite video, and unfortunately, I don't have a volt/multimeter.
I tried to move the HD as far as I could in case that it makes interferences but still I get a lot of snow.
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by aaa801 » Sat Nov 03, 2012 6:09 pm
try connecting a peice of wire from the outer metal bit on the composite cable to earth, its a long shot but it might be the issue
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by JeremyF » Sat Nov 03, 2012 6:58 pm
I would definitely try grounding your Pi, since the Pi has no other ground besides an HDMI monitor, which you don't have.
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by jjggag » Sun Nov 04, 2012 11:20 am
I know that this is going to sound stupid but:
How can I simply ground it? as I am totally noob at electronics, I'm into programming.
The only way I can come with, is to connect the the outer part of the composite cable (the jack connected to the tv) to the analog ground of an arduino that I have, though I didn't try yet as I'm not sure about it and I dont want to burn the arduino :D. Is there, any other simpler way? Thank you!
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by jjggag » Sun Nov 04, 2012 4:52 pm
Ok, I just tried to connect the outer part of the composite video to TP2 (ground) in the raspberry using just a piece of wire with no results.
Its very annoying because apart from the static/snowy image, I also get buzzing (sound).
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by dom » Sun Nov 04, 2012 5:22 pm
jjggag wrote:Ok, I just tried to connect the outer part of the composite video to TP2 (ground) in the raspberry using just a piece of wire with no results.
Its very annoying because apart from the static/snowy image, I also get buzzing (sound).

No, those points will already be connected. You need to connect either of those to a real ground (i.e. something connected to a mains earth pin).
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by drgeoff » Sun Nov 04, 2012 5:49 pm
[quote="jjggag"Its very annoying because apart from the static/snowy image, I also get buzzing (sound).[/quote]
How are you hearing the buzzing sound? From the TV loudspeaker, from the power supply, from the hard disk, ...?
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by michele.x » Sun Nov 04, 2012 6:30 pm
jjggag wrote:Scenario:
Raspberry model B powered by 1A usb.
Hard drive: 2TB WD20Ears 3.5'' so I use this adaptor from sata to usb: http://dx.com/p/usb-2-0-to-sata-ide-5-component-cable-black-10113?item=8 so it's self powered.

I've seen the description and the photos.
Did you use the power supply in the photo to power the hard disc drive?
The TV set you're using uses an earthed plug or has only two pins for the main socket? It's an LCD or CRT model?

I suppose that there's a ground loop somewhere.

With a multimeter I'll check if the molex connector ground is physically connected with the earth ground of the socket. IBM PC and compatible had the earth tied with the 0V of the power supply, so the soap on string supply I suppose is following the standard.

Next I'll check if the tv set has the ground on the rca pin connected to the earth ground pin of the plug.

If both these thing are true a connection earth -> tvset -> composite cable -> pi -> usb cable -> usb hub -> SATA adapter -> hard disc -> power supply-> earth is made. This connection is a ground loop. Colul be a mess to get rid of it.

Do I need a better usb hub providing more Amps? even when the hd is self powered? Or what do you think is the problem? Thank you very much in advance.
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by Burngate » Sun Nov 04, 2012 6:45 pm
Static/snowy image, buzzing sound ...
I'd be wondering if the PSU for the hub is putting rubbish on the ground connection - at its switching frequency or a multiple.
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by jjggag » Mon Nov 05, 2012 9:12 pm
How are you hearing the buzzing sound? From the TV loudspeaker, from the power supply, from the hard disk, ...?

From the TV loudspeaker though is a constant buzzing, no matters if I volume up, it doesnt sound louder. It only goes away if I press mute on tv.

Did you use the power supply in the photo to power the hard disc drive?
The TV set you're using uses an earthed plug or has only two pins for the main socket? It's an LCD or CRT model?

Yes, I use that power supply, it's low quality/cheap but actually it works, and no other problems when using it with a laptop.
The tv set is CRT and it uses an earthed plug.

If both these thing are true a connection earth -> tvset -> composite cable -> pi -> usb cable -> usb hub -> SATA adapter -> hard disc -> power supply-> earth is made. This connection is a ground loop. Colul be a mess to get rid of it.

I used some plug adapters not to use the third pin (earth) on 1 of the sides, and still the same.

Static/snowy image, buzzing sound ...
I'd be wondering if the PSU for the hub is putting rubbish on the ground connection - at its switching frequency or a multiple.

If I dont use the usb hub and I connect the hdd directly to the raspberry, same happens.

Any other idea? Thank you guys for the effort.
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by aaa801 » Mon Nov 05, 2012 9:48 pm
have you tryed earthing the composite cable yet?
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by jjggag » Wed Nov 07, 2012 8:07 pm
I had the opportunity to connect the raspberry to a monitor through hdmi, keeping the rest of the configuration. It worked! noise/snow disappared. So obviously is related to the composite video cable.
have you tryed earthing the composite cable yet?

As I commented, I'm not into electronics so I still don't know how to do this, but probably u're right and that would solve it. I can use a piece of wire, put an end in the outer part of the rca cable and the other one??
Thank u!
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by obcd » Wed Nov 07, 2012 8:58 pm
Connect the other end to mains earth.
Most small adapters only have 2 pins to get mains voltage.
Other equipment like water heaters have an extra pin, or a hole that connects the earth.
It's usually connected to all touchable metal parts of the equipment. Some countries use a third pin which is bigger than the normal ones. Others use a hole in the mains plug and a pin in the socket. Some use a metal strip on the edge of the power plug.
You can usually also use a metal water pipe or cental heating system pipe.
It basically has to be conductive and connected to the earth. That's what the extra connection in your mains socket is connected 2.
Do not connect the wire to one of the mains live connections. (Those used by your supply adapter and every 2 pin mains plug)
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by drgeoff » Thu Nov 08, 2012 12:17 pm
jjggag wrote:I had the opportunity to connect the raspberry to a monitor through hdmi, keeping the rest of the configuration. It worked! noise/snow disappared. So obviously is related to the composite video cable.

You may just have a duff/damaged composite video cable. Can you try another one? For testing it doesn't need to to be a video quality one. If you have a stereo audio cable with a pair of RCA phono plugs (typically red and white but sometimes red and black) at each end, that will do. Just use one plug at each end; same colour of course!
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