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I have a Raspberry Pi 4B and have installed RetroPie on it (by flashing the image provided on the RetroPie site). In the beginning, connecting to my LG smart tv (43UM7600PLB) worked fine. After a while, I needed a couple of tries (it would say 'no signal', and then I'd fiddle with the cables, and in the end it would work). Bot nowadays, I can't get it to work at all. I keep getting 'no signal', no matter which HDMI port I choose on the tv, on the Raspberry Pi, and no matter in which order I plug the HDMI and power cables.

However, everything works perfectly fine on my 10 year old full-HD Panasonic "dumb" tv, and also on my cheap Acer computer screen. So the Raspberry Pi and RetroPie themselves seem to work just fine.

I've seen comments that not shutting down the device properly might break things, and to fix that I would need to re-install the SD card. But if that were the case, would things still work on these other displays?

I've googled around and tried all the things I could find. I connect the HDMI cable to the port closest to the power cable. I've tweaked config.txt in various different ways, including hdmi_safe=1, hdmi_force_hotplug=1, various combinations of hdmi_mode and hdmi_group that people recommended in various forums.

The other day I enabled SSH and looked at the output of tvservice:

pi@retropie:~ $ tvservice -l
1 attached device(s), display ID's are :
Display Number 2, type HDMI 0
pi@retropie:~ $ tvservice -n
[E] No device present
pi@retropie:~ $ tvservice -s
state 0x6 [DVI CUSTOM RGB full 4:3], 1024x768 @ 60.00Hz, progressive

So it looks like it doesn't recognise the tv at all, and now I'm at a loss for what to try next.

What could be the cause of this behaviour, and how can I fix it?


UPDATE after Dmitry's answer:

I have edited config.txt and set hdmi_force_hotplug=1 and config_hdmi_boost=9. Now, if I ssh into the device and do tvservice -n, it says device_name=GSM-LG_TV in the console.

The tv itself still says 'no signal', though.

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This sounds like a classic signal integrity problem.

If you have different cables, test those, perhaps you'll find one that your TV likes better than others. You may also consider buying a new one, especially if the ones you have are cheap, thin and no-name. As always, shorter cables work better than longer ones, especially if the cable is the root cause of signal distortion.

Technically, it's a question of impedance match between the Pi 4 output, the cable, and the TV input, as well as signal attenuation and delay in the cable, but you can't measure all those without expensive equipment.

The other place worth looking into is config.txt. Disable hdmi_safe (it forces default values on some parameters and may interfere with your manual settings), and then try increasing config_hdmi_boost (default value is 5, maximum is 11, a good test sequence is trying 7, 9 and 11, in that order). Note that it makes the signal stronger, not better, so it won't help with a mismatched cable, only with a cable with high attenuation. If the attenuation is low, boosting will only make the signal worse.

If the TV is not getting recognized via HDMI, hdmi_force_hotplug should be sufficient.

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    I don't have another cable, and I don't want to buy another one if I'm not reasonably sure it will work. I got it with my Raspberry Pi starter kit so one would think it would be a suitable cable? But maybe I'm naive to think that :). I tried both config_hdmi_boost and hdmi_force_hotplug before but I don't remember in combination with which other settings, so I'll try those again. What order would you recommend trying them?
    – jqno
    Jul 19 at 10:31
  • I've edited config.txt as you suggested. If I do tvservice -n, it now says device_name=GSM-LG_TV, so I suppose the Pi now recognises the tv. The tv itself still says 'no signal', though. I've updated the question to reflect this new information.
    – jqno
    Jul 20 at 7:18
  • @jqno I don't have any advice to give w.r.t. the cable from the starter kit. I bought a bunch of cheap cables from Amazon, one of them worked, and that's what I use. It's not so much a question of cable quality, more so a question of the match between cable and TV electrical parameters: if the TV input is not 100% HDMI-compliant, then a cheap non-compliant cable might work better than a fully compliant one. Jul 20 at 7:42
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    I've ordered a new cable, but I won't be able to try it out before the bounty deadline expires. Since your answer did move me forward, and yours is the only answer anyway, I'll give you the bounty.
    – jqno
    Jul 23 at 9:10
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    It did! I've accepted your answer.
    – jqno
    Jul 28 at 17:48

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