Issues with 3D printer hotend

[tyguy2]

So I was running my 3D printer today, and for some reason, the hot end does not want to heat up (pictured below is the one time it actually heated up). It has a hard time reaching 150 C, let alone the 230 degrees C needed to melt ABS. It takes ages to get to 230 C, if it does at all. Most of the time it fails and calls a system halt between 150 - 180 C. It took me 10 minutes to get to 230 C, where it normally takes me 2. If I move my motors, the temp will change violently, dropping off quickly. I though perhaps it was a PID autotune error, or perhaps a power supply fault, but after running PID autotune (which determined my max hot end temperature was 156 C  ) and replacing the power supply with a 500 watt ATX power supply, the issues persisted. I though perhaps it was the MOSFET's driving the hot end, but surely they would fail spectacularly rather than work inconsistently, correct? I'm not sure what's going on here, and I'm at a complete loss. 

[tyguy2]

I did that, and the sensor reading are about the same.

[ConKbot]

Check your wiring. Make sure any screw terminals are fully tightened, and see if the last bit of wire going into the cartridge heater isnt partially broken. It sounds like the heater isnt delivering enough power, and if it's getting a clean 12/24v (measure with a dmm on dc and then ac, you should get about 0v ac when the heater is running full power on warmup) then the only thing left is to replace the heater.

[Brumby]

This:

Check your wiring. Make sure any screw terminals are fully tightened, and see if the last bit of wire going into the cartridge heater isnt partially broken.

Mechanical movement causing electrical aberrations is a sign of a mechanical problem with the circuit paths.

If the above doesn't yield you any joy, try wiggling parts of the wiring, connectors, sensors, etc. to see if you can localise the fault.

[sleemanj]

Check your wiring. Make sure any screw terminals are fully tightened,

This!  Too often have I seen posts to reddit etc of a 3d printer control board melting down (with the smokes and the flames and the running and the screaming) because of poor screw terminal connection.

[Dago]

Which thermistor are you using? 100k one?

[Jeroen3]

Did you check if there is at least the expected amount of power going to the heater?

[tyguy2]

I'm getting 12 volts on the heater. I'm using a 100k thermistor that was provided with the E3D lite6.

[kezat]

Might be worth checking if the temp sensor or heater connections are shorting to the heater block, could cause strange temp readings and spikes as your seeing. Also check the resistance of the heater cartridge and if you can move the carriage around and see if the resistance changes as your doing so to check for wiring faults.
Might be a good idea to reset any PID auto tune changes you did until you solve the heating issue.

[tyguy2]

I've reset the PID, and the printer seems to be able to keep a semi stable temperature if I heat up the hot end in 20 degree invervals. Even then, though, the temp does drop sometimes. I'm not sure how to check current draw in the heater, because I'm not sure if my multimeter can handle the current (it's a cheap RadioShack one). Finally, I checked the thermistor and heater block, and moving the motors, jostling the wires, etc doesn't change their resistance.

[charlespax]

What machine do you have? Is this new behavior?

[tyguy2]

It's a custom build printer, but I figured out the issue. One of the MOSFET's blew up today on my RAMPS board. I ordered a new one that can handle more amperage, and got a new fuse to use instead of these polyfuses, ugh. Damn shenzhen components.