Fresh v3 build - "Heater decoupled" after two prints

[jeffnic]

The printer hot end will not heat. About 30 seconds after turning on the extruder heat, the display changes to 'def' for both readings and the display reads 'Heater decoupled'. Red LED's light up on both the hot end and the Rambo when heat is enabled. After powercycling, the temperature readings on the display seem to be inline for room temp - both are around 27-28 degrees. The bed will heat up just fine.

Most forum advice on this is to make sure the thermistor is correctly soldered to the small board on the hot end, so we've resoldered once - even swapped the thermistor (no change). The thermistor we removed read about 91 ohms at room temperature.

This started as an intermittent problem. This problem happened on the first attempt to print, while heating up. We power cycled the printer and it temporarily resolved it. After that, we were able to print two jobs - it failed again while printing the 3rd. Now the issue is persistent.

This is a new build (Max v3) and our first 3d printer, so we don't have a lot of experience. All parts are stock (as came in the kit) and the controller is running firmware version 0.92.2. We're using MatterControl v1.5.

BTW, we followed the instructions in the article https://seemecnc.zendesk.com/hc/en-us/a ... ot-heat-up It's basically checking for LEDs and retightening all connections to Rambo. We verified Red LED on Heat0 and also on the extruder when heat is enabled. We also reseated the connector for Heat0 - no change.

Before we start throwing parts at it, does this sound like a failed thermal fuse? It seems the printer is turning on the heat, but not sensing a change so it errors. What is the logical way to troubleshoot this?

Any help is appreciated.

[Xenocrates]

Logically, if you have a multimeter, check the voltage drop across the thermal fuse. if it's more than a volt, it's probably the thermal fuse. I would ensure the connector is properly and completely seated (I realize that if the LED's illuminate, that should be fine, but humor me by doing that first). If you see no voltage drop across the thermal fuse, either no voltage is getting to it no matter it's state, or it's fine. Check the voltage drop from the + and - heater leads at this point. If there is voltage across them, then check the resistance. It should be in the range of 3.5-5 ohms. If it's more than that, there's an open (Opposite of a short, no connection). If it's less, there's a short, partial or dead. If there's simply no voltage, check the fuses on the Rambo board itself.

Hope that this helps at all.

[morgandc]

Since it is failing while moving, I would pull the connector to the HE280 and wiggle each of the wires and see if are connected well. The other option would be to put both in preheat and then wiggle all of the wires you can get to and try and cause the problem in a more controlled manner.

[jeffnic]

Logically, if you have a multimeter, check the voltage drop across the thermal fuse. if it's more than a volt, it's probably the thermal fuse. I would ensure the connector is properly and completely seated (I realize that if the LED's illuminate, that should be fine, but humor me by doing that first). If you see no voltage drop across the thermal fuse, either no voltage is getting to it no matter it's state, or it's fine. Check the voltage drop from the + and - heater leads at this point. If there is voltage across them, then check the resistance. It should be in the range of 3.5-5 ohms. If it's more than that, there's an open (Opposite of a short, no connection). If it's less, there's a short, partial or dead. If there's simply no voltage, check the fuses on the Rambo board itself.

Hope that this helps at all.

Here's what we've found so far.
We pulled and checked the F3 Rambo fuse which controls heat output to the extruder (location on this page: http://reprap.org/wiki/Rambo) - it was OK. The other two fuses were also OK.

We checked voltage on the + and - connections on the 'Hotend Accelerometer Probe PCB Board' by putting one probe of the meter on a black wire(ground?) on the Rambo board and holding the other probe on each lead - we got 10.84 on one side and 12.26 on the other.. a drop of 1.42V.

We then checked resistance across the thermal fuse and got between 2.8 and 2.9 ohms. This seems a little low - so we have a possible partial short - maybe? We also wiggled and retightened / reconnected everything but of course, no change in the problem. Could this be a fault board - since we're seeing voltage on both sides?

[Xenocrates]

It sounds like you have at least a partial open on the ground from the HE280 to the rambo. That's the only reason you should be seeing more than a miniscule voltage between the black (V-) wire on the rambo and the - terminal on the hotend board. I would see if you can't stuff your probe into the heater v- spring clamp temporarily, and see what the voltage drop is from there to the rambo screw terminal. If that's low, then see if you have a voltage drop between the solder point on the board, and the wire side of the connector. If that's high, then you do actually have a faulty accellormeter board.

[jeffnic]

Thanks everyone for the help

It turned out to be a faulty connection from the thermal fuse to the heater cartridge. It's connected by sliding the two leads through a ferrule and then crimping. Apparently we hadn't gotten it crimped well enough.

[skyjuice]

I'm having the exact same issue. I checked the crimp on the thermal fuse and got the light to come on (red) indicating that there is power going to the heater, but no heat then DEF followed by decoupled. Ideas???

[geneb]

If the thermistor is reading "def", it's because of a wiring problem.

g.

[jeffnic]

Yep - check for shorts from the fuse lead to the hot end heatsink too.

while troubleshooting, I'd opened a support ticket and they said it may be a bad fuse.. So we partially disassembled the hot end and removed the fuse. We checked it and it was good. While pulling it out, it came out of the crimp easily (just fell out really) which is why I said it was a bad crimp. While putting it back together we accidentally let the red insulation slip a bit - so the fuse lead was touching the heat sink on the hot end - we saw the original problem again until we fixed the insulation with a bit of Kapton tape.

[skyjuice]

Very interesting! I will double check that crimp and make sure it isn't just loose. There is defilitely power getting down there as all LED's on the RAMBO light up that need to (H0 and H1) and the leads on the resistor register 3.4-3.4 ohms. I'lll check back in a minute after I check the crimp.

[skyjuice]

Well, the crimp was very tight and snug. Hmmmmm

[czecht]

Did you fix the problem and what did you find the real problem was? How did you fix it? Thanks.

[jeffnic]

Yes, we found two problems.. a bad crimp on the fuse and the red insulation on the crimp had slipped so the fuse lead was grounding out against the heat sink on the hot end. Once we corrected those problems, it ran fine.