SoliForum - 3D Printing Community — Hotend Problems! Thermistor reading negative, then DEF.

Re: Hotend Problems! Thermistor reading negative, then DEF.

2015-07-10T23:38:38Z

martin18991 wrote:

So with the hotend assembly out, everything works. As soon as I touch the frame of the hotend to the frame of the carriage, it shorts. What can I do to insulate the board? I feel like anything I do with washers and such will mess up the alignment of the filament through the hotend?

The only purpose the board serves is the filament sensor to detect when filament runs out and it is a pass through for the thermistor and fan. If you can get nylon washers or you could even remove the board and put several layers of kapton tape over the back then poke holes for the screws and remount it. Ideally though you should try to find why is is shorting. Maybe a lead left too long or something. Because it is mounted with no washers or insulation on all of our machines and shows no signs of shorting. You could also maybe try fiber washers like the ones you get with a PC motherboard mounting kit.

Re: Hotend Problems! Thermistor reading negative, then DEF.

2015-07-10T23:29:44Z

So with the hotend assembly out, everything works. As soon as I touch the frame of the hotend to the frame of the carriage, it shorts. What can I do to insulate the board? I feel like anything I do with washers and such will mess up the alignment of the filament through the hotend?

Re: Hotend Problems! Thermistor reading negative, then DEF.

2015-07-10T23:21:01Z

Roger that, as I was thought. Thanks for your help Carl, I'll have to continue searching. I'll let ya know!

Re: Hotend Problems! Thermistor reading negative, then DEF.

2015-07-10T23:19:02Z

martin18991 wrote:

I should be reading big resistances between the block and the leads right? I don't think the thermistor is shorting like that. I even pulled the thermistor out of the head, and I still have the same problem.

If you get a low reading on one of the thermistor leads in reference to the heat block even with the thermistor removed that still points to one of the leads from the thermistor to the pcb then to the motherboard being shorted to the frame or other metal part somewhere. Both leads when measured in reference to any metal part should be in the meg ohms. If it is low like several hundred or less then the wire is shorting to the frame somewhere and that will cause the issue you are seeing. Unforuntaly I do not remember which of the wires in that 6 pin rainbow cable are the thermistor. You would need to measure with a continuity tester from each pin of the thermistor port to the 6 pin cable and figure it out.. That little PCB board is just a pass through for thermistor.

Re: Hotend Problems! Thermistor reading negative, then DEF.

2015-07-10T23:02:03Z

I should be reading big resistances between the block and the leads right? I don't think the thermistor is shorting like that. I even pulled the thermistor out of the head, and I still have the same problem.

Re: Hotend Problems! Thermistor reading negative, then DEF.

2015-07-10T22:46:15Z

Then one of the thermistor wires is shorted to the brass heat block.

Re: Hotend Problems! Thermistor reading negative, then DEF.

2015-07-10T22:44:45Z

The upper pin of the thermistor plug I get 0 and the lower one I get 26kohm

Re: Hotend Problems! Thermistor reading negative, then DEF.

2015-07-10T22:30:54Z

martin18991 wrote:

If I turn the printer on with the thermisor unplugged, it starts up at 0, and stays there. then as soon as i plug it in, it goes negative then DEF. I ran a tester on the plug, and am getting the 81ish kOhms from the plug to the thermistor.

Measure from the brass heat block to each pin on the thermistor plug. See what reading you get.

Re: Hotend Problems! Thermistor reading negative, then DEF.

2015-07-10T22:14:18Z

I've double and triple checked every connection, and cant see a problem. I do think that it is a grounding issue, I just cannot find it. It works out of the carriage, then as soon as I drop it in, it fails.

Re: Hotend Problems! Thermistor reading negative, then DEF.

2015-07-10T19:28:15Z

If I turn the printer on with the thermisor unplugged, it starts up at 0, and stays there. then as soon as i plug it in, it goes negative then DEF. I ran a tester on the plug, and am getting the 81ish kOhms from the plug to the thermistor.

Re: Hotend Problems! Thermistor reading negative, then DEF.

2015-07-10T19:14:57Z

Sounds like a bad connection at the PCB in the head.

Hotend Problems! Thermistor reading negative, then DEF.

2015-07-10T19:08:06Z

Printer fail at a cruicial time at work guys!!

I have the 1.0, its been printing like a champ, but recently, it's had problems with the extruder temp. The temp reads negative, then goes to DEF whenever I turn the printer on. I thought the thermister was being shorted or something, so I removed it and pressed the tubing up to the edge of the thermister to fix it, resealing it with some RTV. The assembly turns on and works fine, reading room temp when i have the hotend assembly out of the carriage, but when I put it back into the carriage and turn it on, it starts having the same error. I've been trying to search for a shorting cable or something somewhere, but Im at a loss. The carriage has to been grounding the thermister or something. I was thinking maybe it has something to do with the motherboard programming thats actually activating the hotend once its back in the carriage, but I really have no idea.

Any advice would be greatly appreciated.