CTC thermocouple temperatures reading too high

[Alex_9]

My CTC Bizer dual arrived with several things wrong with it. I have run service and support for MakerBot 3D printers and know them well - so I already upgraded the extruder, tightened the frame and got it printing OK.

The temperature reported by both thermocouples at room temperature is about right - IE it matches my MakerBots and RepRaps which use different sensors.

At printing temperatures, the thermocouples both seem to report far too high. For a period I could use the machine, but I had to set the print temperature to 270 degrees C to print ABS. A few degrees lower at 265 and it would print weakly with stringing and underextrusion, a few degrees lower still at 260 and no extrusion at all.

Now, things seem to have got worse, and I cannot print at all. Raising temps between 275 and 280 the printer tries to extrude, weakly, getting better with more temperature, but at the safety limit of 280 in MakerBot Desktop, it’s still unable to print at all. This goes for both extruders.

I hadn’t tried any serious printing on the left extruder until I tried swapping to it as a result of this issue so I can’t say whether they have both gone wrong in the same way - but the current behaviour is very consistent between them.

My question is - do I have 2 faulty thermocouples, is there a known issue with the way these are wired, or is there calibration that can be done to sort these out? If necessary I have a spare genuine MakerBot thermocouple I could try, but prefer to keep that unused unless necessary.

I was using the firmware 7.2 (with bits of Sailfish I believe) that came with the CTC. I upgraded to MakerBot’s 7.6, the latest available via MakerBot Desktop, this made no difference. I’m trying to run from MakerBot Desktop (was 3.9, now upgraded to 3.10).

Hope CTC or a fellow owner can help - got no meaningful response from my eBay seller…

Thanks! Alex

[Rob_Lee]

Change the thermocouple first, they usually are the problem.

[Furious007]

If they are both acting unilaterally it could be a case of the thermocouples haven’t been wired in correctly, maybe check the main board and see if they are both wired in at all and see if they are wired the same. Then compare to a diagram of an image of how they should be connected. Other than that I would say as the seller for replacement thermocouples, my left thermocouple broke about a month ago(annoyingly just after the warranty ran out) and I can seem to find one anywhere apart from flashforge.com but the price is ridiculous and I have to pay for shipping which(because I live in the U.K but the part comes from America) is nearly the cost of the part. So wilhildt you have a valid warranty get a replacement part if you can.

[Alex_9]

Anybody encountered this?

I did get a response from my seller, who sent a pair of new thermocouples and heaters. I have replaced both (4 components changed). Everything is wired 100% correctly.

EXACTLY the same issue persists - all the behaviour is exactly as it was.

Could there be an issue of profile or firmware?

Thanks, Alex

[Alex_9]

An update for anyone who reads this:

I solved the issue, when I had a moment to properly run diagnostics.

TL:DR - The fix was to replace the PTFE linings of the hot ends.

How this pattern of error works:

I believe that the original PTFE linings were of poor quality, and began to degrade when I attempted to print in ABS at only 235-240 degrees (As reported by the Mightyboard/thermocouple combination, which tends to report around 10 degrees higher than RepRap RAMPS/Thermistor combo for the same temperature).

It’s possible that either the PTFE material was poor to begin with, or perhaps more likely the length of tube was too short, allowing a bulge to develop at the bottom, which required a higher temperature to soften it enough to work.

Then, turning up the temperature initially unblocked printing, but above 250 degrees or so it would have begun to degrade the PTFE tube significantly, so eventually the tube was ruined (fused to the also cooked filament inside).

It’s odd that the symptoms were so linear - a steadily increasing temperature at which printing would occur - and so similar for both nozzles. This didn’t help diagnostics, as it pointed me towards the thermocouples.

I have now ordered new nozzles, a short section of PTFE tube with outer diameter (OD) 3mm, inner diameter (ID) 2mm. These were cut to about 31mm long which was slightly too long, I shaved tiny amounts off until it fit up the heatbreak. It was a very tight fit to get the PTFE up the heatbreak - I first inserted some filament to guide the PTFE and keep it from compressing too much, then used needle nosed pliers to push the tube up.

Now, I have printed several items in PLA successfully, I will try ABS again and see how it goes!