sudomod

Posted: **Sun Aug 06, 2017 1:41 pm**

Hi everyone,

I'm just starting out my very first build but I would love some help with the screen connections.
I'm using a Raspberry Pi 3 and I soldered PP24 to the yellow cable of the screen. No output.

In an effort to debug it, I tested the connection with a Raspberry Pi 1 Model B (I only have a cable for the old Composite Video connection and not the new 3-way Audio+Video). It worked.

: twirl.jpg (871.48 KiB) Viewed 8655 times

I then touched the Composite Video Out with the screen's yellow cable like so:

: touch.jpg (623.71 KiB) Viewed 8655 times

And it worked...... but only when I have the yellow RCA connector plugged in anyway!

Knowing that the yellow RCA plug usually has a grounded cable for shielding, I tested the Raspberry Pi 3 pin while connecting the yellow RCA cable to the RP1 Model B's plug (that should provide the ground but not the video). I got the same black screen as before.

The questions are:

What do I need to do in order for the pin to output without a connected cable?
What can be the problem with the Raspberry Pi 3? I'm waiting for a new 3-in-one RCA cable to further test it.

I hope the post was clear but please let me know if I can improve it.
I'm thankful for any help that you can offer me.

Posted: **Mon Aug 07, 2017 8:39 am**

Does your pi 3 works with an HDMI display?

Posted: **Mon Aug 07, 2017 9:55 am**

By default, the Pi3 Disables Hdmi output, when you insert a RCA.
However, the problem can be in your config.txt, maybe you should take a look there.
Idk if you can make a screenshot of your config.txt and post it here, so we can see.
I guess av is disabled and hdmi is priority 1, needs to be changed.
It should work fine with AV/RCA, unless the wiring is done wrong, or config.txt

Posted: **Mon Aug 07, 2017 1:22 pm**

Both Pi work fine with HDMI and I'm using the same SD Card to test them, so I doubt it's config.txt's fault.
Full disclosure: because I'm using a Rpi3 Retropie image, the old Pi falls back to terminal on boot, stating "Illegal instruction". I'm not too concerned because it's precisely that same Pi that works fine with RCA.

Here's my config.txt in any case:

Code: Select all

# For more options and information see
# http://rpf.io/configtxtreadme
# Some settings may impact device functionality. See link above for details

# uncomment if you get no picture on HDMI for a default "safe" mode
#hdmi_safe=1

# uncomment this if your display has a black border of unused pixels visible
# and your display can output without overscan
disable_overscan=1

# uncomment the following to adjust overscan. Use positive numbers if console
# goes off screen, and negative if there is too much border
#overscan_left=16
#overscan_right=16
#overscan_top=16
#overscan_bottom=16

# uncomment to force a console size. By default it will be display's size minus
# overscan.
#framebuffer_width=1280
#framebuffer_height=720
framebuffer_width=320
framebuffer_height=240

# uncomment if hdmi display is not detected and composite is being output
#hdmi_force_hotplug=1
#hdmi_ignore_hotplug=1

# uncomment to force a specific HDMI mode (this will force VGA)
#hdmi_group=1
#hdmi_mode=1

# uncomment to force a HDMI mode rather than DVI. This can make audio work in
# DMT (computer monitor) modes
#hdmi_drive=2

# uncomment to increase signal to HDMI, if you have interference, blanking, or
# no display
#config_hdmi_boost=4

# uncomment for composite PAL
sdtv_mode=2

#uncomment to overclock the arm. 700 MHz is the default.
#arm_freq=800

# Uncomment some or all of these to enable the optional hardware interfaces
#dtparam=i2c_arm=on
#dtparam=i2s=on
#dtparam=spi=on

# Uncomment this to enable the lirc-rpi module
#dtoverlay=lirc-rpi

# Additional overlays and parameters are documented /boot/overlays/README

# Enable audio (loads snd_bcm2835)
dtparam=audio=on
gpu_mem_256=128
gpu_mem_512=256
gpu_mem_1024=256
overscan_scale=1

Thank you both for taking the time to help.

Posted: **Mon Aug 07, 2017 1:40 pm**

Okay, Make a Copy of your config to save for later if this doesn't work.
Copy this text and save it as config.txt and put it on your SD.

Code: Select all

# For more options and information see
# http://www.raspberrypi.org/documentation/configuration/config-txt.md
# Some settings may impact device functionality. See link above for details

# uncomment if you get no picture on HDMI for a default "safe" mode
#hdmi_safe=1

# uncomment this if your display has a black border of unused pixels visible
# and your display can output without overscan
#disable_overscan=1

# uncomment the following to adjust overscan. Use positive numbers if console
# goes off screen, and negative if there is too much border
#overscan_left=16
#overscan_right=16
#overscan_top=16
#overscan_bottom=16

# uncomment to force a console size. By default it will be display's size minus
# overscan.
#framebuffer_width=1280
#framebuffer_height=720

# uncomment if hdmi display is not detected and composite is being output
#hdmi_force_hotplug=1

# uncomment to force a specific HDMI mode (this will force VGA)
#hdmi_group=1
#hdmi_mode=1

# uncomment to force a HDMI mode rather than DVI. This can make audio work in
# DMT (computer monitor) modes
#hdmi_drive=2

# uncomment to increase signal to HDMI, if you have interference, blanking, or
# no display
#config_hdmi_boost=4

# uncomment for composite PAL
sdtv_mode=2

#uncomment to overclock the arm. 700 MHz is the default.
#arm_freq=800

# Uncomment some or all of these to enable the optional hardware interfaces
#dtparam=i2c_arm=on
#dtparam=i2s=on
#dtparam=spi=on

# Uncomment this to enable the lirc-rpi module
#dtoverlay=lirc-rpi

# Additional overlays and parameters are documented /boot/overlays/README

# Enable audio (loads snd_bcm2835)
dtparam=audio=on
gpu_mem_256=128
gpu_mem_512=256
gpu_mem_1024=256
overscan_scale=1

Posted: **Mon Aug 07, 2017 1:43 pm**

Didn't check if they where the same or different, this one is from my pi3 wich works, so you meight give it a try.

Anyhow, we're gonna make your RCA work.
I think you should uncomment this one anyway ,

# uncomment for composite PAL
#sdtv_mode=2

Remove the #

So will be : sdtv_mode=2

I aready did this in the post above this one, good luck, and report here if it worked out for you or not.

try it with a # also , just try both! i think @ the pi3 it has to be done manually like this, other pi's it goes automatically

hope you don't have a NTSC screen

Posted: **Mon Aug 07, 2017 4:01 pm**

Same exact result with all variants of config.txt.

Let me stress that I'm not using an RCA cable on the RPi3, I'm trying to connect PP24 from the RPi3 to the screen, is that what you're doing as well with your Pi3? Check the red circle in my photo for a RPi1B equivalent.

So right now my hypothesis is:
If the RPi1B composite pin doesn't work unless the real yellow RCA cable is connected (even if the yellow is cut off), I'll never get this to work in RPi3 without using a cable as well OR getting the RPi1B to work without the dummy cable. Could it be that the pin only outputs if the port has a cable OR the entire port is missing? That would mean this would never work without completely desoldering the port.

These are just thoughts, if any can confirm or deny this please do. I'm at a loss otherwise.

Posted: **Mon Aug 07, 2017 5:12 pm**

Arlanthir wrote: ↑
Mon Aug 07, 2017 4:01 pm
.

Here you go: https://cdn.instructables.com/FT9/38Q3/ ... MEDIUM.jpg
(it's not really pp24, but right below left) on pi3 it should be pp24 leading there anyway..

Anyway, you can touch the wire here to be sure if it works, see : https://cdn.instructables.com/F20/EET3/ ... MEDIUM.jpg
Boot it up it should work. otherwise there's something wrong.
Don't forget to connect ground also, not just the rca wire alone.

Let us know.

Greets 144Tech

Posted: **Tue Aug 08, 2017 4:06 pm**

Well this was a very newbie mistake. I was connecting the shielding ground of the yellow RCA to the RPi1B because I didn't have a plug for the RPi3 port. I didn't know it made a difference but the ground needs to be from the same Pi as the video signal. I improvised a connection between the yellow RCA and the RPi3 ground and it worked as expected.

I used port PP24 for the video signal and a GPIO pin for ground.

Thanks for all your help and I'm sorry for wasting your time!

Posted: **Wed Aug 09, 2017 3:58 am**

Haha, no problem, already thought you didn't connect the ground.. that's why i said once again.
It was really strange otherwise..
Glad it's fixed

Greets 144Tech

sudomod

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