NOT under X, which is OK. The text from the raspberry pi 3b+ (in contrast to the text generated by the computer on the same monitor) on the basic console screen is very dim. Is there any way to make it brighter?

Are you using a converter cable or is it straight HDMI?

Does the monitor have dual inputs?

You do not want to manually adjust the brightness?

Does the Pi have a sufficient power supply?

The video chip on the Pi might be faulty.

Are you using a converter cable or is it straight HDMI?
Does the monitor have dual inputs?
You do not want to manually adjust the brightness?
Does the Pi have a sufficient power supply?
The video chip on the Pi might be faulty.

Converter cable. Dual inputs. Nothing else needs brightening. 2A power supply. Video chip seems to be fine. Everything under raspbian is fine. Everything is fine (including the prompt) except the text in the console font (NOT X) under slackware, which is what he uses for programming/editing.

Continuing...
Can you please detail what Slackware ARM version are you running on it and how did you install it (which method).
It'll be useful if you could upload somewhere your /boot/config.txt if it contains some parameters that are not commented out (have # in front). Actually, if there are not that many, you can paste here all the active parameters from /boot/config.txt

Coming back to this. You stated that by booting Raspbian in the same HW configuration (display connectivity) gives you a brighter text console.
By default, Raspbian has all the options in /boot/config.txt disabled, except turning on the audio: dtparam=audio=on
This is what led me to believe that you might have some other options enabled in /boot/config.txt for your Slackware installation.
There are many related to the video configuration, not sure if any of them could influence the brightness:
https://www.raspberrypi.org/document...g-txt/video.md

I'm rarely booting Raspbian, mostly for getting the kernel headers for the official Raspberry kernel, but I don't remember observing any brightness differences between the Raspbian console and the Slackware one, for both Slackware ARM 14.2 & -current.

You can apply a "trick" that I'm using on very old/tired displays when working in bright environments, setting the console text on bold white - actually it will be bright white:
If you want to make it default for the active user, just create a file .bash_profile in the home of the user and put the command from above inside it.
Note that with this you'll loose some highlighting defined in /etc/DIR_COLORS, which is the file you can play with for defining your own shell colors, together with /etc/profile for defining the shell prompt colors & other personalizations. Handle with care.
https://unix.stackexchange.com/quest...ll-environment

Another option would be to boot the latest official kernel from Raspberry, the one Raspbian is booting and check if you still have the brightness problem.
If you want to try this, go to the section "Follow the manual installation method" from this post:
https://www.linuxquestions.org/quest...4/#post5862696
Use the latest Raspbian image:
http://director.downloads.raspberryp...retch-lite.zip
Use the default /boot/config.txt and /boot/cmdline.txt that you extracted from the Raspbian image and don't forget to modify the /boot/cmdline.txt before you reboot, like this (check with mount or cat /etc/fstab to make sure your root partition is on /dev/mmcblk0p2):
P.S.
If you like to change the console font, you can use setconsolefont
https://docs.slackware.com/slackware...e_console_font
And this might be also useful for orientation:
https://docs.slackware.com/howtos:cli_manual:shells

1 members found this post helpful.

Thanks!

You're welcome!
I'm wondering what exactly worked? The setterm "trick", setting the character color on white bold ?
If you're satisfied with the resolution, please put the thread on resolved.