3D Printers

FDM 3D Printer General Principle of Operation

There are a few different design philosophies for 3D printers, but many of them share the same roots. Debugging and diagnosing printers can be relatively straightforward once you know how all the parts interconnect. The general working principle is a positioning system with limit feedback, a heating element with temperature sensors and extrusion mechanism, a power supply, and a control board running firmware.

Positioning System

There a few a different positioning systems commonly used on 3D printers. This includes Cartesian (XYZ), Delta, and CoreXY. Each of them has their positives and negatives, but outside of this, debugging them is fairly straightforward. If you think you have an issue with the positioning or extrusion motors, you can test this easily by feeding the printer the G code for the axis you believe is faulty. You can find this information easily by reading the reference for your firmware. For example, here is the gcode reference for printers running Marlin. Just direct one of the axes to move back and forth and see if it works. This also works for the extruder as long as there is no filament loaded.

Problem	Solutions
Motors not driving at all	Change the channel of the stepper; i.e. plug X into Y, or any other known working channel. This should tell you if it's the motor or the driver chip. Do you hear a stalling or whining sound? It's likely the driver chip is busted. Check windings on stepper to make sure no damage. If other motors work in that channel but the specific one doesn't, the stepper may be dead. Check for continuity on the windings; it should be two sets of windings, so there should be two pairs of pins that are connected. If they measure open loop or one of the windings is bad, the whole motor will not work. Replace.
Motors only go in one direction	Driver chip failure. Replace.
Gets stuck driving one axis during initialization or finishes initializing immediately without moving	Check that your limit switches work and are hooked up to the correct place. Use continuity mode to verify that the switch reads open while not closed, and then less than a few ohms when closed. If you recently updated the firmware, make sure that the firmware has the polarity of the limit switches set correctly (switch polarity can be set in here)
Printer does not recognize the SD card	SD card is damaged. Replace. SD card is improperly formatted. Compare with the user manual or the filesystem of the OEM card included with the machine, if available. Debris in SD card slot. Especially common in industrial settings. Clean slot with compressed air and try again. SD card slot damaged. Inspect and resolder if necessary. SD card may be locked, Check the lock switch on the side of SD card, and position the switch to the upwards position.
New printer turns on but is not recognized by the computer when connected via USB. Stepper motors stuck, hot, and buzzing. The user interface does not respond. No physical damage found.	Firmware corrupted from the factory. Flash the appropriate firmware for your model.

Heating Element/Hotbed

If you suspect the heating element is not working, you are likely right. It's very obvious to tell. However, to guarantee that you're telling the printer that you want the temperature raised, you should reference the gcode and directly send the command yourself (there could be unexpected behavior inserted by your slicer during gcode generation that gets in the way of heating; you never know).

Problem	Solutions
Hotend temp not stabilizing	Perform a new PID autotune: connect to your printer via a software that allows you to send it custom gcode commands. Pronterface works well for Windows and Linux, Repetier-host also works for Apple systems. Send the printer an M303 E0 S200 C8, where M303 is the general PID autotune command, E0 is your hotend heater, S is followed by your target temperature (set this to the temp you usually print at, 200 is an example) and C followed by a number 1–15 is the amount of cycles you want the tune to run. 8 should be fine for most cases. WARNING: Stay near your printer and be ready to pull the power, as a bad heater and/or a bad thermistor could be responsible for this and if thermal runaway is not enabled on the printer, further damage could occour.
Hotend not getting hot	Heating element broken. Check resistance. It should not measure open (OL); it should have a resistance anywhere from a few ohms to a few kiloohms. Heating element driver transistor is busted. Check the power transistor that runs the heater- see if it gets warm while use. If it stays cool, it might be broken. If it gets scorching hot, it is definitely broken. It's possible the reason the element is not being heated is that the thermistor for temperature feedback is broken and telling the control board that the element is too hot. WARNING: Stay near your printer and be ready to pull the power, as a bad heater and/or a bad thermistor could be responsible for this and if thermal runaway protection is not enabled on the printer, further damage could occur.
Thermistor failure	Check the resistance of the thermistor back at the plug where it goes into the control board. Bend the cable back and forth in your fingers. The continuity shouldn't drop out. Hold your fingers on the bulb of the thermistor. If the resistance doesn't change while warming, it is likely broken.
Printer shutting down when heating up	- Check the resistance of the heater back at the plug where it goes into the control board. If the resistance is unusually low, the heater could be shorted. - Check the connections on the back of the heater to make sure the bare wires are not touching each other or the heatblock and causing a short. The round heater may need to be rotated to avoid the wires touching.

Control Board

The control board is usually a pretty simple microcontroller, but have become a bit more advanced recently. The low end of these boards usually run an ATMega 8-bit microcontroller, but now you can get them running full 32-bit ARM microcontrollers. This also houses the driving amps for heating the hotend and bed, as well as the stepper drivers for controlling the positioning system.

Problem	Solution
Can't upload firmware	Unplug everything extra from the board, so it's just the microcontroller itself. Try again. Try hitting the reset button after initializing firmware update.
Motors don't work	See above section on stepper motor diagnosis.
Heating elements don't work	See above section on heating diagnosis.
Rebooting erratically	Check power supply for ripple and make sure connectors are well seated.
Safety features not enabled	Ensure correct firmware is installed. Some less scrupulous manufacturers irresponsibly disable safety features in shipped firmware to decrease print failure chance.

Power Supply

These are typically just Meanwell generic Chinesium power supplies. Depending on your printer, you may have a 12 V system or a 24 V system. 24 V systems are generally used for printers that have larger motors and better heating elements. Doubling the voltage means halving the current needed, leading to cooler and longer lifespan for the control board. These are easy to replace as long as you can find one with the connector you need to pair it with your control board.

Problem	Solution
Erratic behaviour	Check the power supply. If excessive ripple has developed, this can cause the electronics to act up. Check both the main supply (12 V or 24 V) and the low side supply (5 V) if present. Check for frayed wires that might have been rubbing against something. Check stepper motor cables are seated correctly Check stepper motor drivers are seated correctly in the board (if you have removable driver PCBs)
System turning on and off mid-print	Check voltage levels. If the levels are consistent, take a look at your connectors. Check motherboard's power input screw terminals for loose connections. High current wires tend to get hot and may melt the connector housing plastic, causing the pins in the connector to lose connection. If this is the case, replace the connector. Don't play with this sort of thing, unless you want a house fire.

Extruders

This is the component that pushes the filament from the spool and out of the nozzle. There are two main categories of extruder, these being bowden and direct drive, both coming with their pros and cons.

There are many different types of extruder that fall into the two categories; most extruders can actually fall in both, depending on their installation. The most common ones include but aren't limited to: MK8 (no gear reduction, single drive), Titan (3:1 gear reduction, single drive), BMG (3:1 gear reduction, dual drive).

Problem	Solution
Clicking and skipping	Check for clogs. Check extruder idler tension. Make sure the hotend is set at the correct temperature. Re-level your printing bed. Clean extruder drive gears and replace if worn out. Check the filament path. If it's a bowden system, make sure there are no kinks on the tube. Some high-end bowden tubes with low tolerances could have issues with lower quality filament. Make sure extruder motor is getting the right amount of current. Too little and it might not have enough power to overcome the filament pressure, too much and it will overheat, drastically decreasing its torque. Check if flow rate is set correctly in the slicer software. An abnormally high extrusion rate could also cause over-extrusion. If you are printing using a large diameter nozzle or particularly fast, the hotend might be having trouble keeping up heating all the material passing through. If that's the case, a better hotend or a higher temperature could be the solution.
System not extruding the correct amount of filament	Check your print settings. Everything flow related (wall flow, infill flow, top layer flow etc.) will cause issues if set to extreme values. These names are pretty standard, but they could change slightly from one slicer to another. Calibrate your esteps. If you're starting to have these issues long after owning the machine, this is unlikely to be it. Doesn't hurt to check though! Check the solutions stated above. Whether they cause skipping or under-extrusion depends on the severity of the issue. An untreated under-extruding system will eventually start skipping steps. The feeder's gear might be silently slipping. If the gears are turning but the filament is not moving, check for blockage or clog in the extruder. A "notch" might appear on the filament where the gear slipped.

Nozzles

Available in different materials and sizes, nozzles melt and deposit the filament to the print bed (and subsequent layers on top). They are one of the many parts that make up a hotend assembly, directly in contact with the heater block and the heatbreak.

The standard brass nozzles are incredibly cheap and easy to replace (we're talking ≈$2 for a pack of 10 shipped), so in the event of a clog you'd be better off getting a new one.

Note: Some material like glow-in-the-dark filaments, carbon fibers filaments, wood filaments, and other exotic filaments can cause extremely fast wear of brass nozzles. If you are using these types of filament, a stainless steel nozzle is recommended.

Problem	Solution
Inconsistent extrusion	Worn nozzle. It's time for a replacement.
Nozzle clog	Overheating heatbreak: the heatsink isn't doing its job, check the cooling fan. Replace the nozzle, but only after fixing the culprit. Improperly maintained nozzle: often happens when using different types of plastics. Plastic "A" might leave some residue in the nozzle that can't be extruded at the printing temperature of plastic "B". Attempt a cold pull, or just replace the nozzle. Temperature is set too high. Some materials will start degrading or burning if the temperature is wrongly set too high. (For example trying to print PLA using gcode meant for ABS)
Plastic leaking out of hotend	Teflon-lined hotends: the PTFE tube inside the heatbreak doesn't make proper contact with the nozzle, giving the filament room to melt out of its designed path. Heat up the hotend (unless its thermistor or heater wires are damaged. In that case, some if not all parts of the hotend need replacement) and see if you can remove the plastic mess. If this doesn't work, some parts of your hotend need replacement—likely the heatbreak, heater block, or nozzle. This can be prevented in the future by loosening up the nozzle a bit, pushing the PTFE tube all the way and locking it in place with a collar clip (or simply a zip tie around the fitting) Full-metal hotends: the nozzle was improperly installed, causing it to no longer make a seal with the heatbreak. Can be caused by not using enough torque when installing the nozzle or, most commonly, not performing a hot install. Most hotends need, in fact, to be at a printing temperature (≈200 °C) for a nozzle swap as the materials contract and expand in different amounts. Same fixing procedure as the teflon-lined hotends.
Extruding works when replacing the filament but not during a print	Re-level your print-bed, often this means that the bed is too close to the extruder and not allowing the melted filament out. Depending on the filament type, the actual material may be bad/old. In the case of PLA, if it has been unsealed for a long period of time theres a chance after you insert it into the extruder and start a print, the filament may snap since it has become brittle and un-usable. If this becomes a major issue, it's recommended that you get vacuum sealable bags to store your used PLA spools in-between uses

Printbed

Also referred to as build plate, this is where the first layer gets laid down. It's important to have a well maintained bed, allowing the plastic to stick when it's supposed to and get released after the print is competed.

The most common print beds in cheap consumer printers are made of glass, either plain or textured. Glass is hard, flat and consistent: this helps keeping the cost down, as the heated bed below it doesn't require tight tolerances as it simply conforms to the glass. It also has no issues with adhering to the most common materials, assuming it's a clean surface.

Cleaning glass is very simple: a low amount of high concentration isopropyl alcohol will wipe away any oils that might impact adhesion.

Another common material to print on is PEI, as its sheets can be applied to any surface and, like glass, can come in plain or textured. PEI sheets are usually combined with a magnetic spring steel plate which allows for convenient and simple removal of prints, by flexing the plate and literally popping them off.

Problem	Solution
Prints not sticking, detaching mid print	Check bed level. If the nozzle is too high from the bed, the plastic will have bad adhesion. Clean your bed. If the problem persists, try adding a thin layer of glue stick or hairspray to the surface.
Prints not releasing from surface	Use a sharpened spatula. If you still can't get it off, try putting the build plate in the freezer or under cold running water. If your printer supports it, put the build plate back into the printer and enable pre-heat or set the bed temp as high as it can go, you may be able to soften the bond and pull off your print. Check Z-Offset height if using an auto levelling probe, too large of an offset can drive the nozzle into the print bed causing the print to bond heavily to the print bed.

SLA 3D Printer General Principle of Operation

SLA 3D printers can create high accuracy parts with relatively simple components. The most common type of SLA printers used by hobbyists and makers is MSLA. The general working principles of MSLA printers is a UV backlight combined with a LCD screen, Z-axis with build plate, controller board running firmware, and usually a brick power supply separate from printer.

LCD

The LCD is responsible for creating the mask of the image in order to develop layers of the print. LCDs don't last forever and need to be replaced when problems arise. There are two main types of LCDs used on MSLA printers: Color LCDs and Mono LCDs. Mono LCDs let more light trough then color LCDs which allow for faster layer exposure times. Mono LCDs also last longer than color LCD because there are no sub pixels and color filters.

Problem	Solution
LCD not displaying image	Expose the entire LCD with the printer's menu. If you see the backlight turn on, but the LCD does not let light through, your problem is most likely with the LCD. If the UV backlight does not turn on when exposing the display, the problem is most likely with the backlight. Check if there is any physical damage to the LCD like cracks. Check if the LCD ribbon cables are correctly plugged into the control board. Check the LCD ribbon cable for damage. Replace LCD if all other solutions don't work. Problem could also be with controller if LCD still dosent work after replacment.
Spots on LCD are dead when exposing, or spots missing in prints.	Usually caused by the heat from the bright light emitted by the UV backlight causing degradation on the LCD. Replace LCD.

UV Backlight

The UV backlight is responsible for emitting light to the LCD, and then to cure the resin. The UV backlight is usually found in two versions: a single or group of LEDs in the center with a cone shaped reflector, or the newer style parallel LED matrix backlights that have more even exposure. With both versions, there is usually a small board separate from the controller that is responsible for driving the UV backlight.

Problem

Solution

Backlight not working

Check power going to the backlight from the backlight driver output. If there is power, and the backlight is still not on, the problem is the backlight. Check power going into backlight driver, and the signal wire going to the driver in some printers. If the driver is not getting power or a signal from the control board, the problem is the control board. Check wires going to driver and backlight. Check the printers power supply as it might be broken and not be able to supply enough current to turn on the backlight. Replace the backlight, or what you find to be broken from the above testing. Also, make sure the cooling fan for the backlight is working as the backlight may have failed by over heating due to having no cooling.

Z-Axis

The Z-Axis is responsible for raising and lowering the build plate. It is usually driven by a stepper motor and a leadscrew, with a linear rail as a guide. Printers usually have either one or two linear rails to guide the build plate. As with any moving mechanism, lubrication is important. Any PTFE or silicone + PTFE lubricant works well on the leadscrew and rails of a printer.

Problem	Solution
Ripples or waves on print surface	Caused by wobble in the Z-Axis, try tightening build plate bracket screws going into linear rail carriage. Check if there is play in leadscrew nut, replace if necessary. Check stepper motor mount for play. Check if leadscrew is bent by raising the build plate and looking for wobble in the leadscrew.
Z-Axis wont move	Check stepper motor cables going to controller. Stepper motor could be dead. Stepper driver might be busted, replace control board or driver if necessary.
Z-Axis makes loud noise	Limit switch problem, Check cables and small metal rod that activates the switch if its an optical switch.

Control Board

The control board is responsible for driving the LCD screen, UV light, Z-Axis, and any other components like fans and the touch display.

Problem	Solution
USB stick reader not working	Some printers have a USB extension cable from the port outside to the control board, make sure it is plugged in. Check if USB stick is working on a computer. Check if the slicer filetype is compatible with the printer. Replace board or connector if other solutions don't work.
No power to printer	Check input terminal on control board. Check barrel jack input and power wires. Check power supply. Check fuses if any. Check switch on printer.

FDM 3D Printer Model Specific Information

Lulzbot Taz / Lulzbot Mini

Problem

Solution

Z axis minimum endstop not triggering

Cause could be a design flaw with the Z min endstop, it's rather easy to accidentally bridge the Z min microcontroller input to the hotend power, frying the microcontroller input. Source replacement microcontroller chip Atmega 2560, desolder and replace, program Arduino bootloader using ISP connector and AVRISP2 , then load firmware downloaded from Lulzbot. Long term-solution would be to have some opto-isolator in-circuit to prevent fat fingers with metal tools from bridging hotend power to the nozzle.

Creality CR-10

Problem	Solution
Temperature Fluctuations	Some CR-10 boards have a capacitor with too low of a value (100 μF 35 V) for the 5-volt supply, creating problems with the microcontroller. To fix this, replace it with a higher capacitance value (such as 220 μF 16 V)

Anycubic Kossel Linear Plus

Problem	Solution
Hotend Temperature Fluctuations	1. Check to see if the part cooling fan / hotend cooling fan is blowing on the heater block and/or thermistor. If so, move fan duct or fan itself away from blowing on the heater block and/or thermistor. 2. You may need to perform a PID tune for your specific heater cartridge. You may also need to do so if you have re-flashed your motherboard or even if you've changed out your nozzle size/material. Refer to PID Tuning In 10 Easy Steps for steps on how to perform a PID tune of your hotend. 3. If your printer is giving you THERMAL RUNAWAY error messages, DO NOT CONTINUE TO PRINT! Verify that your thermistor is reading correctly by using a hair dryer to heat up the hotend. If that is reading correctly then you may need to change out your heater cartridge. If the thermistor is not reading correctly or is fluctuating greatly, you may need to either perform a PID tune of the hotend or change out your thermistor for a functional one. Some more helpful resources for diagnosing hotend faults: 3D Printer hotend won't heat up - Diagnosing - identify Fault - Replace Ceramic Heater Cartridge anycubic kossel heater repair
Bed Temperature Fluctuations	1. Check to see if the bed is plugged in and is hooked up to the correct power outputs according to your user manual or motherboard manufacturer. 2. You may need to perform a PID tune for your specific heated bed. You may also need to do so if you have reflashed your motherboard or even if you've changed out your bed size/material. Refer to PID Tuning In 10 Easy Steps for steps on how to perform a PID tune of your bed. You may need to search for specific commands, the ones in the video are strictly for hotend tuning but the steps are the same. 3. Make sure the motherboard is working. There have been instances in which the motherboard's sockets for the heated bed get loose and do not connect the heated bed to the motherboard anymore. In this case, verify that the heated bed's leads are secured in place in the sockets of the motherboard and that the wires are making a secure connection to the motherboard.
Excessive Gantry Movement / Excessive Layer Shifting	1. The gantry itself may be loose. Make sure all screws are tightened and that the gantry is solid. A little bit of wiggle is fine but not excessive amounts. 2. Check G-code to verify that it is reading out correct speeds and feedrates. You also should verify that the printer size is correct in the slicer software you are using.

Prusa i3 mk2s

Problem	Solution
MinTemp Error	If your 3D printer is kept in a cold room (below 22 °C) then move it to a warmer room, or take a soldering iron and manually heat up the hot end by placing the iron on the hotend and holding it there for about 1 minute. The error should go away after that. This was a common problem in the mk2, and it's a bit annoying, but you can read more here

References

Is your 3D printer a fire hazard? How to test Marlin safety features