Arduino or Ramps problem?

Printer running fine for almost 2 years. Smartrap, and very pleased with it.
Had to unclog the hotend nozzle, unfortunately, when I put it back together the heater element slid out of the block, the flex then broke off one of the wires.
No probs I thought, simply bought another heater element, 40w, and fitted it.
I replaced the thermistor at the same time. I have a bag of them, so it was the same spec as previously.

Problem:
The thermistor is reading an accurate room temp.
The hot end heats up (though not as quickly as it did with the old heater element).
The LCD is showing the rising temperature and the print temp.
When the print temp is reached, the printer starts the self levelling process
The hotend temp stays at print temp.
Then:
As soon as the printer starts the print process it appears that the power to the heater is cut,
The temp drops all the way back to around 140 degrees, and then seems to stay there.

I have reloaded the configuration software onto the 2650, but it is still the same.
All connections are secure.

Does anyone know what I should replace?
Would the new heater element cause this?
Has the Arduino blown a component?
Is the RAMPS board a likely cause?

If anyone can point me in the right direction I would be very grateful.

Many thanks

Rob

A 40W heater element is usually an upgrade to the more common 25W version. You're saying it takes longer to heat up than before.
So my first guess is, there is something wrong with the specs of the heater ( maybe 40W@24V ? ) or the wiring has bad contact. What does the multimeter read? ( resistance/ current ?)

Nevertheless, you should start autoPID tuning, to set new PID values. It either runs OK afterwards or there still is a fault in the wiring.

Thanks for the information.

I took a look at this.

PID Tuning

I was suffering a few of these symptoms, eg Rise to 160 degrees, very slow to 200 degrees.

I will order a 25w heater, and try again, it was heating perfectly/printing perfectly before, so the 40w heater may be an issue.

Quote
Wibbles
As soon as the printer starts the print process it appears that the power to the heater is cut,
The temp drops all the way back to around 140 degrees, and then seems to stay there.

Does the temp *really* drop, or is it just the thermistor reading that drops? When the temp is showing 140, can you melt PLA on the outside of the nozzle?

What changes when the printer starts to print? Is it the movement of the hot-end that causes the temp change? Or the start of extrusion? Or something else? Try heating the nozzle

My guess is that your heater cartridge or thermistor is loose, and the motion of the hot-end pulls them out of position.

Another possibility is that one of your thermistor or heater wires are broken inside the insulation. There will be no visible break, but as the hot-end moves, the broken ends will touch and connect, then move apart and disconnect. Or that there's frayed ends sticking out from the heater cartridge... these can move and short out, so little current goes to the heater (and the short glows white-hot... don't ask how I know!).

The cure for all the above is to have the bundle of wires from your RAMPS rigidly attached to the hot-end, so that any flexing of wires is done by the whole bundle. Otherwise flexing of individual wires close to the hot-end will cause them to break, or touch each other, and generally be unreliable.

Edited 1 time(s). Last edit at 01/08/2017 06:58PM by frankvdh.

The temp drops, the heater is held in with an allen screw, and the thermistor is held in with Kapton tape. These were the first thing that I checked, they are still both firmly in place, I can see them while I am typing this.

The head definitely cools. The printing process starts, and it gets as far as the brim layer, but then it has dropped down far enough to prevent the pla from flowing.

It drops as soon as the Gcode switches from bed levelling to printing. It is visible on the lcd display.

I checked the thermistor wires, they are good, and insulated with heatshrink, and kapton tape. It could be a faulty thermistor, it's always a possibility, but it's not a random thing. It does exactly the same every time, the temperature drops off as soon as the printing starts. I am guessing that this is when the PID settings start playing a part. The head is moving all over the print bed during bed levelling and it stays on the temp, it is only when it starts to print that it decides to drop.

The wiring is all enclosed in cable wrap, and then tie wrapped to hold it all in place. There is minimal movement on the cables. It's worked fine for 2 years.

My guess is that I need to recalibrate the AutoPID as the new heater element is 40w and the old one may have been 25w (I honestly have no idea what that one was, it came with the printer). The heater element was the only part that was swapped out, and that was when the problem occurred. The PID detection process is something that I had never heard of before, as with most things, I don't see these requirements until I get a problem. It's all part of the learning curve.

Just for good measure I have ordered another 2560 and Ramps, and will start again from scratch when they arrive.