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I have two identical setups with 5" TFT displays connected to Raspberry DPI hats. The SD card images are identical. The only difference is one is using a model 3B and the other a model 3B+. I have the 3B config.txt set up for 800x480 vertical display. The Pi(s) boot to the command line and I can access both using SSH. The 3B produces a clear image. The 3B+ is not driving the video HSYNC or VSYNC. What is the difference between models? Here is the config.txt

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

# This configuration is for DPI 800x480
#---------------------------------------

# Disable spi and i2c, we need these pins.
dtparam=spi=off
dtparam=i2c_arm=off

# Set screen size and any overscan required
disable_overscan=1
overscan_left=0
overscan_right=0
overscan_top=0
overscan_bottom=0
framebuffer_width=480
framebuffer_height=800

# enable the DPI display
enable_dpi_lcd=1
display_default_lcd=1

# set up the size to 800x480
dpi_group=2
dpi_mode=87

# set up the hsync/vsync/clock polarity and format
dpi_output_format=454661

# set up the size to 800x480
hdmi_timings=800 0 40 48 88 480 0 13 3 32 0 0 0 60 0 32000000 6

display_rotate=1
gpu_mem=256
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    Your config file indicates your display is set to merely 480 wide by 800 tall. Normally it's the other way around (800 wide by 480 tall). Was this intentional? – Tim Campbell Mar 4 at 23:08
  • Take the working SDCard from your 3B and boot it in your 3B+. You may need to run sudo apt update && sudo apt dist-upgrade -y first if the 3B SDCard is too old for your 3B+. – Dougie Mar 4 at 23:34
  • The framebuffer is set to 480 wide by 800 tall because this is needed to get the display to be vertical. "display_rotate=1" by itself is not enough. – Tim Trudeau Mar 5 at 14:10
  • Swapping the SD cards was the first thing I did. I have run update and upgrade. The only variable is the 3B+ Pi. I am wondering if there is something in the device tree that is different? – Tim Trudeau Mar 5 at 14:13
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I was able to solve the issue by adding

#Set DPI overlay mode
dtoverlay=dpi18

Now both versions of the Pi work the same.

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