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  1. #1
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    How I fixed my Chinese TB6560 controller (updated)

    I purchased a 4-axis controller base on the Toshiba TB6560 Driver IC from a Hong Kong vendor thru e.b.a.y. Although the board could be made to function by setting all parameters to low / relaxed / lame, I decided to find out why the controller greatly underperformed as compared to what the TB6560 IC specification implied.

    Performance issues of MY board:
    - required maximum (slow) timing settings in EMC2 to work without missing steps
    - could be made to work at 12v but not 24v without missing steps
    - would work with drive current set to minimum (25%) otherwise motors would miss steps
    - at working controller settings, rapids weren't rapid...

    All of these factors suggested a noise problem in the circuit (faster timings = less noise margin, higher drive voltage = more switching noise, higher drive current = more switching noise, rapid rapids = more switching noise).

    Disclaimer: The information here pertains to MY TB6560 board which may not be the same as YOUR TB6560 board. Use the information here in at your own risk. I accept no responsibility as to the application of this information to YOUR board. However, the information is believed to be correct and does seem to have completely fixed MY board.

    A schematic did not ship with my board. Another e.b.a.y. customer had requested the schematic from the my vendor, but the vendor response was "we dont do that". So I developed my own schematic based on inspecting and measuring MY board. See attached.

    Seven issues were identified with the design on MY board:

    1) Driver IC CLOCK input improperly driven: The TB6560 uses the rising edge of the CLOCK input (not explicitly called out in IC spec except for “rising edge” symbol shown in one table). The slow turn off time of the opto-coupler combined with the passive pull-up resistor are insufficient and allow system noise to cause unstable driver circuit operation. ( I measured a rise time with and oscilliscope of app 50uSec on my board.) Solution: Actively drive the CLOCK input using added 74HC14 IC as buffer.

    2) Driver IC ENABLE input improperly driven: The opto-coupler for the ENABLE input is wired incorrectly having the npn emitter connected to supply. Although the circuit does function, the improper wiring of the npn will cause very low transistor gain opening the possibility of system noise corrupting the ENABLE signal. Solution: Rewire the npn of the opto-coupler with collector to supply and emitter to output.

    3) Drive Current Manipulated by CLOCK/STEP signal: It appears that an attempt was made 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 was active high. And 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
    Solution: Disconnect the non-spec circuit.

    4) Activity LED improper function: The activity LED circuit works properly when the STEP signal from the PC has high duty cycle (active low orientation). However, the TB6560 spec directly states that proper operation requires low CLOCK (e.g., STEP) signal duty cycle (or active high orientation). With active high orientation signal the activity LED remains lit even when the driver is not being ‘stepped’. Solution: None. Ignore the LEDs.

    5) Potential for Overheating of 12V Voltage Regulator: The cooling fan is fed directly from the 12V Vreg output adding significantly to the loading of the device. The 12V Vreg will shut down if it overheats protecting itself; such a shutdown would result in lost steps of an active motor. Solution: Power the cooling fan with an external supply or (with suitable step down circuit) from the stepper motor supply voltage directly. With the fan connected to the 12v Vreg the heatsink temperature was 155 F, disconnecting the fan and waiting 5 minutes, the 12V Vreg heatsink temp dropped to 125 F.

    6) System Not Optically Isolated: Despite having opto-couplers on all PC inputs and output, the controller does not properly implement optical isolation of the PC from the driver IC’s nor from the stepper motor power supply. This is due to sharing of ground among all circuits. Solution: None. However, do assure PC and stepper motor power supply externally share the same earth ground.

    7) Operating Voltage Mis-information: The board is marked for input voltage “12v to 36v” but the IC spec indicates maximum operating voltage of 34V. But even that is probably not a safe operating point due to potential stepper motor generated voltage spikes. The controller board output diodes will clamp large overvoltage spikes when the diode breakdown voltage is reached, but the breakdown voltage is likely above the maximum voltage the driver IC can sustain without damage. Solution: Recommend limiting input voltage to 30v or less to provide margin of safety for operation.

    Update: Immediately after posting the fixes, it occurred to me that it would be better to buffer the CLOCK/STEP signals with 1 74HC14 inverter instead of 2 :
    - allows the 'activity LEDs' to work (using 1 inverter and setting software to invert the clock)
    - allows 1 IC to 'fix' a 4 or 5 axis board instead of needing 2 IC's
    - simpler to wire
    See attachment slide10ver2.jpg for updated fix. I tested this morning and works fine.
    Attached Thumbnails Attached Thumbnails cntr_top.jpg   cntr_bot.jpg   bufbrdmntd.jpg   Slide09.JPG   Slide10ver2.jpg  

    step_waveform.jpg  
    Attached Files Attached Files

  2. #2
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    Bravo on making the effort to examine in detail how the driver board is actually wired, and what design decisions (and possible mistakes) were made by some anonymous board designer on the other side of the world.

    I'm considering getting a board that looks suspiciously like the one that is shown in your photos, and so I'll have to take a closer look at the TB6560 spec sheet and reference design and compare it with your reverse-engineered info. Thanks...

  3. #3
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    Very well thought out!
    I do not own one of the boards you mention but you have done everyone that owns one a great service.

  4. #4
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    great!. Many thanks for share. I have same issues on my 3 axis board, with 1 motor seems to work fine, but when try with 2 o 3 motors the steppers do not work fine (some step stalls on all motors). I replace some parts (tb6560, capacitors, added pullup without good results). I am going to try your fix .

    What do you think about the capacitor used for clock? I think that could be lower value for decrease the needled pulse time.

    (Sorry my Spanglish )

  5. #5
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    Quote Originally Posted by villamany View Post
    great!. Many thanks for share. I have same issues on my 3 axis board, with 1 motor seems to work fine, but when try with 2 o 3 motors the steppers do not work fine (some step stalls on all motors). I replace some parts (tb6560, capacitors, added pullup without good results). I am going to try your fix .

    What do you think about the capacitor used for clock? I think that could be lower value for decrease the needled pulse time.

    (Sorry my Spanglish )
    villamany,

    The capacitor on OSC does set the step pulse time as you indicate. I was not able to determine the value of that capicitor on MY board and I could not get my half-working oscilliscope to trigger properly so that I could measure the frequency on the OSC line. The silk screen on MY board says "102" which usually stands for "1000" and since the TB6560 IC spec says acceptable values are 100pF to 1000pF one would think the cap is 1000pF. But there are several parts on the board that whose values do not match the silk screen...
    With that said, I am unsure if changing the OSC cap will help or not. On MY board the rise time on the step/CLOCK was simply too long. I did try changing
    the step/CLOCK pull-up resistor from 4.7k to 1.0k which changed the rise time from 50uS to app. 20uS as measured on my o-scope; this change seemed to reduce the missed steps by only a small amount; only by adding the buffer with its very fast rise time was I able to eliminate missed steps (the 74HC14 biffer IC spec says rise time is less than 0.020uS or 1000 times faster than without the buffer, e.g. 20nS)

    At what voltage are you trying to run your controller ? Without the buffer, I could get 12v to work but never found any settings that allowed 24v to run properly.

  6. #6
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    at 13.8v i get some step stall, at 24v are very more step stall.

    The stall are increase with:
    - more steppers connected.
    - with more torque settings.
    - with more voltage.
    - with less time decay settings.
    - with low microstep settings.

    Seems to be also noise problems.

    What are the added resistors that i can see on "cntr_bot.jpg" picture?.

    I only need 4x10k resistors, 1x74hc14 ic and 1x decouplig capacitor for these mods is ok?.

    I has my controller working for about 5hours without problems on 12v regulator (very hot for my hand but not thermal shutdown ocurred).

  7. #7
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    A buffer board schematic for your consideration

    Quote Originally Posted by villamany View Post
    at 13.8v i get some step stall, at 24v are very more step stall.

    The stall are increase with:
    - more steppers connected.
    - with more torque settings.
    - with more voltage.
    - with less time decay settings.
    - with low microstep settings.

    Seems to be also noise problems.

    What are the added resistors that i can see on "cntr_bot.jpg" picture?.

    I only need 4x10k resistors, 1x74hc14 ic and 1x decouplig capacitor for these mods is ok?.

    I has my controller working for about 5hours without problems on 12v regulator (very hot for my hand but not thermal shutdown ocurred).
    villamany,

    The 4 leaded resistors that can be seen on "cnr_bot.jpg" were my attempt to fix the controller by changing the STEP/CLOCK pull-up from 4.7k to 1.0k. I did this by leaving the 4.7k in place and adding 1k resistors in parallel between the +5v supply and the Step signal ; the resulting effective pull-up was 4.7k || 1.0k = 0.8k. On my board, the chip resistors and capacitors are glued and soldered down making removal of those parts a little difficult and I did not want to risk damaging any printed circuit board traces by applying enough heat to cause the glue to release.

    For the mod's, you may want 6 resistors as you will not want to leave the unused 74HC14 inputs unconnected; you can tie them to ground or +5v or, as I would suggest, to pull-up resistors. That way if you come across another signal that needs buffering the you will have spare buffers in place.

    To hold my (ver 1) buffer board to the controller I used double sided foam tape (see "bufbrdmntd.jpg - buffer board mounted").

    I have attached a schematic for a ver 2 buffer board for your consideration.
    Attached Thumbnails Attached Thumbnails CNC Controller buffer board schematic ver 2.jpg  

  8. #8
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    Angry Optical isolation fix proposal

    Just ordered a 5-axis version of this board (probably the new one) plus a digital display.

    I haven't modifiet it yet (it works but not very good, now I use it to mill acrylic case for it, later I'll do the fixes).

    I found that it IS possible to add optical isolation to this board! Fortunately this version has all optocouplers connected to +5V at one side and to GND at another. Using a permamemt marker I've drawn a line on the board under optocouplers (on both sides where possible) without crossing any PCB traces. Now it's obvious where exactly the sides are connected. It is possible to cut GND and +5V traces to separate input and output sides completely. I'm going to do that and install a dc-dc converter in place of 78xx regulators.

    Regarding motor noise and driving problems, I think I'll remove these transistors completely without cutting traces. I was unable to measure capacitances at OSC pin without unsoldering, going to measure frequencies later.

    There is one more problem with digital display board. It misses steps! I investigated its design and found that it isusing a MCS-51 compatible microcontroller (STC12C5A08AD) at 24 MHz without any hardware counters. Software polling! It is impossible to use software polling at higher step rates with short pulses. Looking for a way to replace the MCU with a CPLD or something; it were nice to find a pin compatible part but probably it's impossible.

    Another problem is that the display is very dim. It is easy to solve. There are eight 2 kOhm resistors on the board - 5 near MCU and 3 on another side. They set display segment current. (There are no other 2 kOhm resistors on the board). Replace them with smaller value. I found anything around 560 Ohm would be Ok. Smaller values can lead to overcurrent.

    I also got a blue manual control box for this board. It is built around the same STC MCU. It's very useful for stepper testing but quite useless in production work - no need to buy. (I bought it for testing purposes only.) However it can easily be replaced with a simple 555 pulse generator on a breadboard so a bit overpriced.

  9. #9
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    Smile My board

    Hi guys
    I read and reread this post that intend to fix this board. I followed the steps since begin and the first thing that i've done was add another 74hc14 to buff the signal steps, this realy gave me a better board, but i still have the miss steps in all the velocities so i removed the opto acoupler and take the signal directily to 74hc14 added with this modification i have a terrible noise from de stepper motor, i could hear the miss steps. i've put again the optos but i removed all the optos of dir and i've done a jumper between the pin 2 with 4 and all the four axis works very well without miss steps. i removed also the others optor i left only the step and enable optor in.
    Now i have one question, how i put the diodo to protect my boad of back emf from motor and the reley?
    And sorry for my english

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  10. #10
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    Quote Originally Posted by jaclerier View Post
    Now i have one question, how i put the diodo to protect my boad of back emf from motor and the reley?
    For motors: Each winding needs four diodes, two at each output (8 diodes for one motor total). At each pin, one diode to ground (cathode to motor, anode to ground) and one to +12-36V (anode to motor, cathode to power bus). Diodes to ground are on the board already (at least my board has them). Just connect each of the motor outputs to the power rail with a diode (cathode to power rail), now it's Ok.

    For the relay: just one diode between the relay winding pins, also connected backwards.

  11. #11
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    I was considering buying one of these boards, guess I wont bother.

    John

  12. #12
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    Hi folks,

    I'm very new to CNC and have a long way to go no doubt. I have also bought the TB6560 board and have not hooked it up yet and I'm glad I ran across your board fix post first before I do hook it up. I have a question. Should a breakout-board be used with this TB6560 board ? ? ?

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