PSA: Orange Pi Zero expansion board tv-out not working solution
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4 posts in this topic

Having invested many, many hours getting the video out to work on my recently purchased Orange Pi Zero kit, I'd like to leave this heads up for the next person having trouble with video out.  In my case, none of the advice I could find in this forum or elsewhere seemed to make any difference.  If you find yourself in a similar situation, here are some things you should know.

  1. The latest Armbian images for the OrangePi Zero enable composite video out by default.  It should just work.  (Well at least the Ubuntu image -- I never actually verified Debian Jesse worked after I fixed my expansion board.)  You should NOT need to fiddle with /etc/modules or .fex files.  Although that bit of information can be found in other posts on this forum, it took me a while to stumble across it, so I'm calling it out here.
  2. Don't trust the expansion board or your AV cable.  If you hook everything up and don't get video right away, the first thing to try is connecting your monitor directly to the GND and TV-OUT pins on the 13-pin connector.  Regretfully, I only resorted to this after much time spent futzing with other things.  In my case, not only was my expansion board borked, but the supposedly Zune/RaspberryPi compatible AV cable I got from Amazon actually had the ground and video swapped on the yellow RCA plug.
  3. The expansion board adds a bit of circuitry to the tv-out line, an inductor, two capacitors and a resistor, which I'm guessing is some sort of filter that attempts to "clean up" the video signal.  Being that you can hook up video directly to the OrangePi Zero without an expansion board, it would seem this filtering is entirely optional.
  4. I happened to notice (while checking continuity with a multitester) that the resistance between the GND and TV-OUT pins on the bare, unpowered OrangePi Zero board was effectively an open circuit, but when the expansion board was installed, it changed to approximately 50 ohms.  It seemed to me that all this would accomplish is to pull the composite video signal very close to ground and hold it there.  On a hunch, I took an Xacto knife and carefully scraped R359 from the filter circuit off of the expansion board.  This did the trick.  Now, with a proper AV cable,  my monitor could pick up a signal on its CVBS port.  I've attached a picture of the expansion board with the location of this resistor circled in red.  Maybe I just had a bad resistor, but if you've tried everything else, it may be worth knowing that removing this resistor can't hurt and is worth trying.

 

opi0-expansion.jpg

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To add to this: The problem with the TRRS plug is that there exist a few pin/tip definitions so you can never trust any cable and the one Xunlong sells seems to use unusual color coding.

 

And if you solved this problem wasting a few hours of your live then most probably you run in huge overscan issues with your TV that can not be solved on OPi Zero side but only on TV's side (if at all):

 

In other words: consider CVBS broken by design and OPi Zero a headless device :) 

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9 hours ago, davedsbca said:

I happened to notice (while checking continuity with a multitester) that the resistance between the GND and TV-OUT pins on the bare, unpowered OrangePi Zero board was effectively an open circuit, but when the expansion board was installed, it changed to approximately 50 ohms.  It seemed to me that all this would accomplish is to pull the composite video signal very close to ground and hold it there.  On a hunch, I took an Xacto knife and carefully scraped R359 from the filter circuit off of the expansion board.  This did the trick.  Now, with a proper AV cable,  my monitor could pick up a signal on its CVBS port.  I've attached a picture of the expansion board with the location of this resistor circled in red.  Maybe I just had a bad resistor, but if you've tried everything else, it may be worth knowing that removing this resistor can't hurt and is worth trying.

This should implement a basic impedance matching (though it should be closer to 75 Ohms than to 50 if I understand it correctly). All other Orange Pi boards that have CVBS output on the 3.5mm jack have this circuit on the main board.

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On 20. 3. 2017 at 1:20 AM, davedsbca said:

supposedly Zune/RaspberryPi compatible AV cable I got from Amazon actually had the ground and video swapped on the yellow RCA plug.

 

On 20. 3. 2017 at 7:22 AM, tkaiser said:

The problem with the TRRS plug is that there exist a few pin/tip definitions so you can never trust any cable

 

Fortunatelly, most cables/wirings are either OMTP or CTIA compliant. For that reason, I bought cheap OMTP to CTIA adapter from ebay, which solves many annoyances and now I don't need to worry anymore about pinout.

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