[FIX] How to fix Chinese TB6560 Stepper controller

TB6560 based Chinese stepper controllers are damn cheap and many of us bought them from eBay or from other sources. These boards have huge design fault and you'll notice inconsistent axis movement as well as unwanted noise and screaming from the steppers. Here is how we fixed our boards. Hope it will be useful to you.

Anyway, I bought a TB6560 based 3-axis stepper driver couple of months back from eBay for my DIY CNC router. My X-axis was smooth with this controller but Y & Z was screaming and loosing steps. I initially thought it is a problem in the machine so I did lot of modification in the machine but nothing helped. Then I started thinking that it is the controller, most likely the TB6560 in Y & Z is faulty. I decided to replace the chips in the controller. I was about to order the chips but at the last moment I orderd a complete new board instead of chips.

I got my new board in hand after two weeks. But I was simply shocked(!) after connecting the board because new board has exactly the problem I have in earlier one.

One of my e-buddy's also was suffering from the same issue and started tracing the board. After a hard effort finally he was able to draw the schematic from the trace. Then he connected an Oscilloscope and checked the signals (i.e. STEP, DIR etc.) comming from the PC. He discovered that STEP pulses in the input (pin 3) of TB6560 is extremely weak. He used an additional buffer (74LS14) to amplify it and WOW probem is gone. He did the same MOD for all axis and steppers are moving smooth.

I did the same MOD in one of my boards according to his findings but it doesn't work! I also did some other MOD in the board as an experiment. Unfortunately nothing has been fixed my "missing step" issue.

My Oscilloscope is dead so I can't check the pulse status in TB6560 input. But I restored the board in original and did a new experiment. I did bypass the opto-isolator (just for Y axis) for STEP signal and connected on-board buffer output directly to the driver CLK (ping 3 of TB6560). WOW! Stepper is running smooth. No missing steps, no screaming. I did the same MOD for all axis and in both the boards. Now I can even run the machine in higher IPM than before.

Descripting of the fix (see images):

1. Cut the line to bypass on-board opto-isolator.
2. Jumper between on-board buffer output and driver IC.
3. Cut the line to disconnect the non-spec circuit. It was actually an attempt to implement a feature where the driver would reduce current to the stepper motors when the motors were idle. This was accomplished by pulling the drive current set input low when the CLOCK signal is active high. Although the feature does work for drive current settings of 25% and 50%, the implementation has negative side effects that outweigh the feature usefulness:
- the feature departs from the reference design of the TB6560 spec resulting in the spec no longer accurately describing operation
- motors may be overdriven with higher than programmed drive current
- artificially raises the lowest current motor that the controller board can safely drive

[ALL CREDIT GOES TO MY BUDDY WHO ACTUALLY DID THE WHOLE TRACING AND IDENTIFIED THE PROBLEM.]

Enjoy!!

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