truve
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Composite RCA output (solved)

Wed Jan 23, 2013 7:54 pm

This post is to help people who have a problem with composite output. I have solved this myself and I will describe my problem and solution. Relates to the Type 2 (512MB) Raspberry Pi.

The Problem

I needed component connection as my sister has an old TV with only composite. I booted various images - Raspbmc and Wheezy and both had identical problem, no composite output. Both OSs booted perfectly fine but would not output to composite, although worked perfectly with HDMI. Tried booting with composite pulled out and then plugged it in after boot, still no composite. Then I tried botting with composite in and then put in HDMI cable, so now both composite and HDMI were plugged in. Bam! I got composite output. I then realised that it was the voltage/current coming from the hdmi cable that made the composite output work. I found out if I simply just touched the outer metal casing of the hdmi socket on the pi then composite would work, move it off the metal and then composite would not output any longer. I tired this with a usb cable plugged into my pc and then i touched the end again to the metal case of the hdmi connector on the pi board, it did the same thing and the component worked. SO I gathered it was simply the voltage/connection that was needed, I then realised the 3.5mm audio jack from my TV would prob have some voltage/current (to amplify the signal), so I plugged in a 3.5mm to 3.5mm audio jack from the pi to my TV.

The solution

It worked! The 3.5mm audio cable HAS to be attached to your TV too, in order for the component output to work properly and for you to get a picture through the composite.

I hope this saves someone some time, it was beginning to baffle me.

I now need to find out if I can turn this pi into a print (and possibly file) server if that's even possible

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redhawk
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Re: Composite RCA output

Wed Jan 23, 2013 8:43 pm

Something is wrong with your setup I'm using composite video with my PC TV card without anything else connected and it still work if I connect composite video long after booting.
Since the Pi disables the composite video output if an attached HDMI is detected then it's logical to assume your Pi thinks it's attached to HDMI equipment during booting.
I'm not exactly sure how this detection method works but I believe you can force HDMI output to stay off using one of the config.txt options.
If you have a digital voltmeter I would check the voltage between the Pi ground and the ground of the composite cable coming from the TV (not connected to the Pi) there maybe a leak from your PSU.

Richard S.

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Re: Composite RCA output

Sun Jan 27, 2013 11:58 am

...sounds like a floating input to me. If it is, then the mere act of connecting a voltmeter to it may alter the voltage sufficiently to make the thing work, and the voltage you measure will not be what the Pi is actually seeing.
Since you seem to have it working when the shell is touched with a USB cable, perhaps it simply needs a large value resistor (say 1Mohm) soldering on between the shell and ground?
Ta,
Mark
Mark Edgeworth

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Re: Composite RCA output

Sun Jan 27, 2013 2:06 pm

I think that most likely the ground return wire in the composite video cable is broken. When you plug in the audio cable you are providing ground for both as the grounds would be all tied together in the TV.
.
Unless specified otherwise my response is based on the latest and fully updated Raspbian Buster w/ Desktop OS.

SimonSmall
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Re: Composite RCA output

Sun Jan 27, 2013 5:06 pm

Strangely, I get something similar - I had set mine up with the three cables plugged into a Scart converter plugged into the TV. I have not bothered with sound yet, so left it like that until I can plug in a set of powered speakers. It all works fine on the TV (oldish, no HDMI)

When I unplug the audio lead my display goes all fuzzy and unreadable. Plug it back in and it is OK. Plug in the powered speakers, back to fuzzy. I'll check the cables sometime soon.

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Costatec
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Re: Composite RCA output

Tue Feb 19, 2013 4:23 pm

Well done. Saved me time as I only connected the video cable!

DrDoom
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Re: Composite RCA output

Sun Apr 28, 2013 9:27 am

Same problem for me, my little composite monitor 4.3" doesn't display any image.
Then I realized that I was using and old composite audio cable very thin, that has not ground connection.
Just changing this composite cable make it work.
Check that your composite cable has a nice ground shield.

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mahjongg
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Re: Composite RCA output

Sun Apr 28, 2013 1:49 pm

composite cables should always have a ground return, they cant work without one.

DrDoom
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Re: Composite RCA output

Sun Apr 28, 2013 4:33 pm

My mistake was to use a cable from an audio splitter like this:
https://www.google.com/search?q=3+way+a ... a&safe=off
It doesn't have ground! and do not work.
Be warned.

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mahjongg
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Re: Composite RCA output

Tue Apr 30, 2013 12:02 am

Thats cheap! Whoever designed this cable reckoned that all three RCA cables would be used at the same time and that he could get away with using just one GND wire for all three cables! I would feel humiliated as an engineer if I needed to retort to such nastiness just to scrape of a fraction of a cent per cable. I must be the cheapest of cheap Chinese junk! A normal three cable composite of average quality uses three shielded cables!
Especially a video cable (with the yellow plug) needs a good shielding!

bugssoren
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Re: Composite RCA output

Thu May 30, 2013 2:37 pm

This is a common problem with RCA type connectors. Both audio and video. Issue is that there is not a solid ground connection between the source such as the Raspberry Pi and the monitor/TV. Most often this is just a matter of a bad connection between cable and device(s) . The outer metal shell of the RCA connectors can bend if pressure is applied to the cable and connector. Simply unplug the cable. Gently squeeze the outer metal shell with a pliers. Work your way around the shell to get all of the metal tabs slightly more compressed. This will tighten the ground connection to the Pi or TV. Going too far will make the cable difficult to plug in. So go easy and test fit as you go. Also could be either end of the cable or both ends.

Dart
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Re: Composite RCA output

Fri Aug 29, 2014 7:40 pm

I have The composite finally working after I held shift and the number 4. It then asked if you want to make this permanent I selected yes. Now my video works only with Raspbian and does not with Open elect and Raspbmc.

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mahjongg
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Re: Composite RCA output

Fri Aug 29, 2014 8:19 pm

operating systems (except perhaps RiscOs) do auto detect of the HDMI (Switch to composite if HDMI is not detected), and also look at config.txt (NOOBS does neither). perhaps you enabled an entry affecting composite in config.txt, or have HDMI still attached.

fruitoftheloom
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Re: Composite RCA output

Fri Aug 29, 2014 8:21 pm

Retired disgracefully.....
......to a more gentile life !

Dart
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Re: Composite RCA output

Fri Aug 29, 2014 9:09 pm

Composite works with Raspbian but not for Openelec or Raspbmc. How do I get Openelec or Raspbmc to detect composite video. The HDMI is disconnected and since it is working with one OS why not the others?

Dart
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Re: Composite RCA output

Fri Aug 29, 2014 9:25 pm

Under settings in Raspxbmc there is a section calling for Additional config.txt settings. Does anyone knows how to set that up to get the system to accept composite video. Right now the system sees composite video at start up then goes blank. I know that it is working because i have Raspxbmc set up to start playing music. I hear the music but the composite video shuts off after boot.

Dart
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Re: Composite RCA output

Fri Aug 29, 2014 9:30 pm

I just solved it by typing TV=1 under setting Additional config.txt ha ha ha!

Axilot
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Re: Composite RCA output (solved)

Fri Nov 21, 2014 4:10 pm

I've the same problem
Did you find a solutio for openelec also?

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