hot end heat issues

i have a prusa i3. i had the original version and printed the parts for the rework. after i made the parts swap, i've had nothing but print issues. starting off, i had the problem i described here. thought it might be the hobbed bolt, so i replaced it with one that grips great. still having issues. as i was digging in to it, i used a thermal imager to measure the hot end temperature and it didnt appear to be getting hot enough (sw says ~230, but temp readout showed like 120). replaced the hot end, reran the pid autotune, still having issues. figured i might have screwed up my ramps board (accidental short or something), so i replaced that. seems like the problem is the hot end not staying hot enough fast enough, if that make sense. i took everything apart, and pushed the filament through manually (by hand). it seems to push through fine to begin with, then would slow down or become much harder, then as the heating element heated back up, would get easy again, then repeat. i'm sure i can do something in the firmware to decrease the time between it sensing the cool down and heat it back up, but i dont know where to set that at. or, could be all in my head. i'm open to any suggestions.

Have you printed from PC and Did you monitor the heat curve from Pronterface from example? Have you checked firmware / thermistor settings? What firmware? I have Marlin.

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Prusa i3, Ramps 1.4. Catnozzle 0.4mm
SketchUp - Enveloping Globoid Worm Gear - Part One - 3D Printed: [youtu.be]
DesignSpark Mechanical & more precise screw thread: [youtu.be]
Nicer Screw Thread In SketchUp ( Bolts,Nuts): [youtu.be]
How To Model A Heart Shape In SketchUp: [youtu.be]
How To Draw 3D Printable Snap Fit Ball Joint In SketchUp: [youtu.be]

yes i printed from my pc. i used repetier host and the temperature showed to only vary a few degrees before the heater kicked back on. i use the marlin firmware. i have tried different themistor selections in the firmware (config.h). thats about all i know to check. is there something else i can check?

thanks!

Have you checked Marlin: // When temperature exceeds max temp, your heater will be switched off.
// This feature exists to protect your hotend from overheating accidentally, but *NOT* from thermistor short/failure!
// You should use MINTEMP for thermistor short/failure protection.
#define HEATER_0_MAXTEMP 275

Do you have heat bed / hot end wires reversed? Thermistor loose or failing? Just thoughts...

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Prusa i3, Ramps 1.4. Catnozzle 0.4mm
SketchUp - Enveloping Globoid Worm Gear - Part One - 3D Printed: [youtu.be]
DesignSpark Mechanical & more precise screw thread: [youtu.be]
Nicer Screw Thread In SketchUp ( Bolts,Nuts): [youtu.be]
How To Model A Heart Shape In SketchUp: [youtu.be]
How To Draw 3D Printable Snap Fit Ball Joint In SketchUp: [youtu.be]