Blinking LCD (4 replies)

Hi,

I am new to 3d printing and inherited an old selfmade printer with Arduino 2560 and Ramps 1.4. I updated the Marlin firmware to the latest stable version and more or less got everything running with the following exceptions:

• The LCD - RepRap Smart controller - is displaying Text correctly and shows the menus, but it is constantly alternating between the first menupoint and its contents (like blinking). It appears as if the encoder button would be constantly pressed. I assume that either the encoder is faulty, or there must be a short circuit somewhere. However, I could not find schematics for the controller to carry out educated probing of the board.
  Of course, I configured it in configuration.h, but what also caught my attention is that after booting the kill switch was always activated and I had to deactivate the kill switch in the pins_ramps.h for that controller assigning it to pin -1. Another thing is that the reset button does not seem to work.
  I shielded the connecting cables, so that should not be a problem.
• When I first connected the board, the temperature was correctly given for the heatbed. However at one point it went up to 330 ºC without the bed being heated. The previous owner had the kit mounted on a metal screw passing through both boards, so I guess it shorted. Anyway, I mounted it on plastic standoffs to remove the issue.
  Now the issue is that after updating the firmware and loosing the previous settings, I don't seem to be able to find the correct thermistor setting for the bed. None of the available options gives a correct value and the temperatures displayed for the bed by M105 are fluctuating a lot, while the temp reading for the extruder is rock solid. Also, if I remove the thermistor plug for the extruder, the reading reduces to -15ºC. If I do the same for the bed sensor, the reading does not change, but remains at the last read value. Connecting the bed thermistor to the extruder input pins on the board, I get the correct values for room temperature, which tells me that the thermistor setting assigned to the extruder thermistor ("1") should be correct also for the bed sensor. However, if I assign thermistor "1" to the bed pins, the output changes to 90ºC
  I also tried to assign "0" and the experimental value for 25ºC to the bed input. Both return the correct values.

Any ideas about what could be the reason? Is there any reference for testing the board for short circuits? I inspected the solder joints, cleaned it for removing any residual flux, etc. Everything checks out fine, but the above mentioned issues.

Thanks
Berthold