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I'm attempting to get an Elecrow 7" HDMI LCD touchscreen (Amazon UK) to work with my Raspberry Pi 3 B+. Upon following the instructions enclosed with the screen, all I see is "No Signal".

The instructions state that I should add the following to the end of /boot/config.txt:

max_usb_current=1
hdmi_group=2
hdmi_mode=1
hdmi_mode=87
hdmi_cvt 1024 600 60 6 0 0 0

This does not work. I've replaced the whole of config.txt with just the above: still doesn't work.

I've tried it with just the following:

hdmi_group=2
hdmi_mode=87
hdmi_cvt 1024 600 60 6 0 0 0

That is: no max_usb_current (apparently not required for the 3 B+), and remove the duplicate hdmi_mode line. I also double-checked whether the missing = was a typo in the docs. Apparently this line works with either. I've tried both.

Still no luck.

If I boot with hdmi_safe=1, then the screen displays, but only at 592x448, rather than the expected 1024x600. The screen works fine at the expected resolution when plugged into a laptop.

I'm trying this with "RASPBIAN STRETCH WITH DESKTOP", Nov 2018, from https://www.raspberrypi.org/downloads/raspbian/.

What am I doing wrong?

Update: It turns out that I had a spare official Pi PSU (5.1v, 2.5A) tucked away in a drawer. Using that almost works:

  • Power on the Pi with the screen powered from the Pi: No Signal.
  • Power on the Pi with the screen not powered from the Pi: it works. If I then connect the USB cable between the screen and the Pi: it continues to work.

If I power the screen separately from the Pi, the touchscreen stops working. Moreover, if I then unplug the power from the Pi, it appears to draw power backwards from the screen, which seems ... wrong.

Any ideas?

Looking back in Slack history at work, it appears that I successfully had the screen working, in text mode at least, back in August, so maybe something broke between (presumably) the 2018-06-29 and 2018-11-13 releases.

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  • How are you powering the Pi and screen ? What power supplies are you using?
    – CoderMike
    Nov 27, 2018 at 20:15
  • 2.0A 5v PSU from Asus. Not sure where from: Asus T101, most likely. Screen's powered from the Pi; if I try powering it directly (it has 2 USB inputs), the touchscreen stops working. The Pi is showing low voltage (in HDMI safe mode), so I've ordered another official PSU. Would low power result in not being able to drive the screen at the correct resolution?
    – Roger Lipscombe
    Nov 27, 2018 at 21:04
  • But: that's worth a try -- powering the screen (ignoring the touchscreen for now) separately from the Pi.
    – Roger Lipscombe
    Nov 27, 2018 at 21:05
  • I believe low power can affect the hdmi output. I would definitely use the official 5.1V 2.5A 18AWG cable official PSU on the Pi and for testing at least the Asus PSU on the screen.
    – CoderMike
    Nov 27, 2018 at 21:11
  • how do you know that the touchscreen stops working?
    – jsotola
    Nov 27, 2018 at 22:12

1 Answer 1

Reset to default
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The following /boot/config.txt fixes it. In particular, I needed the hdmi_force_hotplug=1 setting (found in a review on Amazon).

max_usb_current=1
hdmi_force_hotplug=1
hdmi_group=2
hdmi_mode=87
hdmi_cvt=1024 600 60 6 0 0 0
#hdmi_safe=1

Since I'm using a Pi 3 B+, I would also recommend an official PSU, but it doesn't seem absolutely necessary.

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