I am using this display with my Pis. Thanks to a tutorial they put some time ago, I have been able to control the brightness on the screen. Recently, I was testing some nodes on the Pi using a continuity tester and while there is no apparent damage to the Pi or any change in its behavior, suddenly the brightness control for the Waveshare 7in is not working.

I tried another one of the displays I have around and brigthtness control does not respond on it either. I tried both displays with a different Pi with no results. Then I tried doing these using a different GPIO pin and have still come up with nothing.

Because of this, I am unable to diagnose the source of the problem.

Is it possible the the displays are now somehow damaged?

  • What does "testing some nodes" mean? What is the "continuity tester"? – Milliways Oct 7 '19 at 5:27
  • Ah, let me see. (1) Pi 1, Mon 1 used to be OK, now (2) P1, M1 not OK (3) P2, M2 not OK either. So my quick and dirty conclusion is that Pi is broken. But then even (4) (a) P1 + M1, (b) P1 + (c) M2, P2 + (d) M1, P2 + M2 all no luck. What would you conclude now? One possibility is that P1 has become a serial mon killer, any mon connected will be killed. – tlfong01 Oct 7 '19 at 5:38
  • And are you doing PWM brightness control? If yes, then I will see if I can give your a postmortem. :) waveshare.com/wiki/File:PWM_control_backlight_manual.pdf – tlfong01 Oct 7 '19 at 5:44
  • And are you using the default GPIO pin #18 as the PWM pin? And has it ever worked once or twice? And now any other pins not working? Are Rpi and mon are still working otherwise? If yes, perhaps only the Rp PWM output and Mon PWM input part is fried. Or you just made the wrong connection and everything is alive and well. There is still some hope! :) – tlfong01 Oct 7 '19 at 5:51
  • 1
    It is easy to check if GPIO 18 is alive. Use any GPIO command/program to set it high or low. If you don't have a multi-meter, use a LED and 1k series resistor to see it can turn on or off. When doing PWM duty cycle check, you can see the LED goes from dark to dim, to bright etc. You should do this dry run before connecting to the mon. – tlfong01 Oct 7 '19 at 5:57

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Browse other questions tagged or ask your own question.