I have finally fixed the problem of missing steps in my Chinese made TB6560 CNC Stepper Motor Controller!
Keep reading for a total overview of all the associated CNC stepper motor controller problems experienced and the reasons for the problems, or jump down the page to get straight to the Step-by-Step guide on how I fixed the board .
This stepper motor controller board fix may look complicated, but with a little explanation and with the help of pictures, the changes should be relatively quick and simple for most people. The board fix should also assist people using similar Chinese made stepper motor controllers (3 axis, 4 axis and 5 axis boards) for 3D printer, laser cutter, plasma cutter and plotter applications.
I have tried to keep this guide as simple as possible so people with little electronics or CNC experience do not get discouraged.
The Initial Problem
Ever since I built my DIY CNC router, I experienced noisy motors, intermittent missing steps and irregular axis travel. My machine was still generally very usable for cutting rough projects, but for finer and more defined work, there were various annoying problems.
Circles were not (always) exactly round. Calibration checks forever seemed to wander and travel distances were slightly different in one direction of an axis travel to the other. Further, I found motors were noisy and ran hotter than I expected they should.
After initially scrutinizing motor speed settings, coupling slippage, lack of torque, backlash, frame rigidity and every other component of my CNC machine, I still found no specific reason for the occurrence of the problems. I came to suspect that something must have been going on with the generation and delivery of motor step signals themselves from within the controller board. A little further investigation of various CNC discussions on the net confirmed this hunch.
The problems stemmed from electronic design within the Chinese made motor controller board. The specific board uses Toshiba TB6560 driver chips (although these chips are not the fault). After a lot of effort in working out the required modifications for the board and correcting most above CNC operation issues as a result, I wanted to help others realize the same success I had achieved from the changes. I offer the following as a how to guide.
While some people may baulk at the idea of butchering their own CNC driver board when it already mostly works, I offer some encouragement. The fix was satisfying and complete. It was also relatively quick, cheap and most of all, EASY. It IS possible to end up with a reliable and fully functional motor driver board with only a small amount of time, effort and understanding invested.
You do not necessarily need to know what components do, or “why” they do it for the solution to work. Just follow the photos and directions I have provided. I will try to keep things as simple as possible.
After saying this, I accept NO RESPONSIBILITY for the accuracy of this information, or the relevance of my experiences to your situation or particular controller board. Any damage you may cause to your own board is on your own head and your own responsibility.
- The TB6560 Stepper Motor Controller Board – Basic Overview
My particular Chinese made 4 axis CNC controller board was ordered online from Ebay in early 2011. The board I am talking about uses the large Toshiba TB6560 motor driver chips at the heart. The missing steps appear associated with the design of board rather than the Toshiba motor driver chips themselves. There are 3 axis, 4 axis and 5 axis variations of this particular control board, with one TB6560 chip driving each axis stepper motor. This fix should be applicable to all boards that are similar to the 4 axis board shown, despite the number of axis included on a board (ie: the required fix is just a simple repeat or reduction of the same wiring to each motor driver chip if there are more or less axis).
- What the Solution Fixes and Achieves Electronically
I won’t go in-depth with the technicals here for fear of confusing less experienced DIYers who just want their controller board fixed as a priority. However, it appears the basic problem is that the design of the board does not allow the main step driver chips to send out “clean” signalling to the motors. Because of the noise in signalling, intended steps may get missed occasionally and the stepper motors therefore do not always advance steps or reversed each and every time they should. This results in intermittent variations in axis travel and cutter head position.
- How Much Work is Required to Fix My TB6560 Board?
Relatively little, considering the results!
To fix the stepping problems, I placed a (very) common, cheap and easily obtained chip (called a Hex Inverting Schmitt Trigger, or 74HCL14 by chip code) into the circuit to turn the original “dirty step signals” into clean on/off steps which the motors can correctly understand and respond to.
The chip is placed onto a small, separate PCB board. It then requires just 6 resistors and 1 capacitor soldered around it to make it work. This separate circuit then requires connection to the main CNC motor driver board in 10 places (for 4 axis boards). Four copper circuit tracks on the CNC driver board then require cutting to allow the new circuit to take over operation.
- 1 x Small piece of grid drilled PCB board (Approx 5cm / 2 inches square would be ample).
- 1 x Hex Inverting Schmitt Trigger (ie: 74HC14 by chip code)
- 6 x 10K Ohmn resisters (ie: Brown, Black, Orange)
- 1 x 1uF capacitor (Code 104)
All components listed are very common and available for only a few dollars each on Ebay or many other online sources.
Introducing the 74HCL14 Chip
No fear! This isn’t rocket science, even if you have never worked with chips before…
- Explanation of the 74HC14 Chip – Knowing These Basics Will Make Things MUCH Easier
Before jumping into this project, it is good to know some of the absolute basics about the 74HC14 chip you need in the circuit. Knowing just a little will save you a huge amount of time in making and checking the required modifications. I will try to keep things simple.
- The 74HC14 Schmitt Hex Inverter Trigger Chip
This 74HC14 chip basically takes noisy input signals and converts them to clean signals (in a nutshell).
The chip has 14 pins in total. Pin 14 receives a 5V+ power supply and pin 7 is a ground pin. So in essence, connecting these two pins to power alone, turns the chip on.
Inside the chip circuitry itself, there are 6 SEPARATE Schmitt hex inverter triggers as shown in Fig 2. Each “Schmitt hex inverter unit” in the chip is serviced by two pins. An input (the signal to be cleaned) and the output (the clean signal for use).
This being the case, the pins on the chip are arranged into pairs corresponding to each of the individual inverter units within the chip.
The pin pairs are pins 1-2 …. 3-4 …. 5-6 on the left side of the chip and 13-12 …. 11-10 …. 9-8 on the right.
Each axis on the CNC Motor Controller Board requires use of one pin pair of the 74HC14 chip for this modification work. Therefore, a modification of a 3 axis CNC controller board will require use of (any) 3 of these pin pairs. A 4 axis motor controller board would require (any) 4 pin pairs and so forth. (ie: The pictures displayed later all show wiring for a 4 axis board modifications.) It doesn’t matter which pin pair you choose to use on the 74HC14 chip for either X, Y , Z or C axis connection, as long as the pins are a pair connected to a separate inverter inside the 74HC14.
All that said ….
1. Go Ahead and Make the Schmitt Hex Inverter Trigger PCB Board Circuit
This circuit is not rocket science, but I have put the layout in a pictorial way (Fig 3) so it is easy to understand for less experienced DIYers. Using the 74HC14 Schmitt Hex Inverter Trigger Chip, 10K Ohmn resistors and the 1 uF capacitor, go ahead and make the required circuit on a separate punched PCB board as per the following diagram. Careful not to apply too much heat to the chip legs! (nb: Use a heat clip while soldering.) This PCB will sit as a separate unit on the original CNC motor driver board.
Note that this diagram is for a 4 axis CNC controller board modification. Therefore, 4 pairs of triggers are used. The remaining 2 spare triggers with the brown lines (ie: pins 3…4 and 11….10) still have resistors connected to the input side for safety reasons, but no output connections.
2. CNC Motor Controller Board Arrangement
The Chinese made CNC stepper motor controller board uses one large black Toshiba TB6560 motor driver chip for each axis. You will see a circuit track between each soldered Optical Isolator output leg and the Pin 3 of the Toshiba TB6560 chips. Identify one circuit track from the optical isolator leg to the TB6560 chip’s pin 3 per axis.
The upper row of connections on the CNC controller board are the optic isolator output side of connections. These are delivering the noisy signal to the pins of the Schmitt Hex Inverter Trigger we insert into the circuit.
The connections on the other side will be the “clean signal” connected to Pin 3 of the TB6560 motor driver chip.
Each circuit track has a mini resister also connected approximately half way along. We will use this bare contact as a suitable point to carefully solder the connection wires (as in the photo) from the PCB you just made.
Note that the copper circuit track of the CNC controller board is the lighter (blue) color of the board, not the dark color (due to there being no copper underneath the lacquer).