I got my Prusa i3 Clear Frame second-hand. The only customizations that have been done (before I bought it) are a LCD display and to put the z-axis probe on a swiveling servo arm. A little calibration and it worked ery well for a good while.
And then in the process of re-assembling the hot end, I broke one of the leads off of the extruder's thermistor. It broke so close to the end that soldering really wasn't an option. So, I purchased another thermistor. Actually, a pack of 6. (I tend to err on the side of having spares. Heh.) Specifically these: https://www.amazon.com/gp/product/B01N4KY6TR/ref=oh_aui_detailpage_o08_s00?ie=UTF8&psc=1
I installed it (had to modify the plug a bit, but it wasn't that big a deal) and started a test print but the extruder just consistently slipped, unable to push the filament through the extruder.
(I apparently let it run long enough to burn out the extruder driver, but that's beside the point. I replaced that and the extruder stepper works again.)
I then did some experimentation. Since I'd replaced the thermistor, the obvious thought was the temperature of the hot end was incorrectly read. I got an infrared laser thermometer and confirmed my suspicion. The readout on the LCD display showed 200C, but the thermometer showed barely 100C no matter where I pointed it. Pressing a bit of PLA filament against the hot end barely made the PLA sticky.
So, I researched the new thermistor a bit and found that somebody else had posted that thermistor table number 11 was the correct setting for it. In the meantime, I'd bought a second Arduino Mega and RAMPS board, so I flashed the firmware to the new Arduino Mega and installed it. I've still got the old Arduino Mega with the original firmware (the version of Marlin on the Google drive page.)
However that didn't change anything regarding the temperature discrepancy. Still barely over 100C when the LCD display shows 210C.
So, finally, I bought the "HotEnd Thermistor With Brass Sleeve" from Folgertech, thinking that would make things easier and remove the thermistor setting from the equasion; once I had that, I'd know the right setting should be 1 (or 6 as is the default in the firmware on the google drive page).
But, no dice. After retrying with the Folgertech thermistor on both setting 1 and setting 6, the laser thermometer still shows a temperature difference of roughly 100C lower than what shows on the LCD screen.
I also tried switching out the RAMPS board and swapping out the Arduino Mega with the old one.
That's basically the entirety of my story. I'm hoping somebody has an idea. I'd appreciate any help you can give me. Thanks in advance!
I threw away my old thermistor, but I really don't think there was much chance of salvaging it anyway.