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  1. #31
    I wish i could remember if i switched the x axis ports around last time i replaced the chip as both x axis motors are interchangeable, i think i did which would help elimenate the motor wiring as it would probably blow a different chip, but i just cant be sure if did infact switch them.

    I do know whci axis motor failed last time though so i will switch ports this time after checking it so that it would blow a different driver
    Last edited by howser37; 02-02-2017 at 04:46 PM.

  2. #32
    GND's Avatar
    Lives in Cambridge, United Kingdom. Last Activity: 3 Weeks Ago Has been a member for 2-3 years. Has a total post count of 60. Received thanks 2 times, giving thanks to others 11 times.
    Can't help you there!!

  3. #33
    after looking at the latest photo
    in addition to adding a wire link to replace the damaged track
    I would resolder the current sense resistor as well

    Click image for larger version. 

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    John

    PS
    if you switch the two X motors now
    then if it fails again you will know if the fault goes with the motor
    Last edited by john swift; 02-02-2017 at 04:58 PM.

  4. #34
    Ok thanks John, will do

  5. #35
    Ok im gonna have a go at this repair tomorrow but just want to check a few things first with you guys as my electronics knowledge is minimal lol,so a few questions.

    1. For the track jumper repair i can only find/source solid core wire with 0.6mm core unless i use something ridiculously thick like a core from lighting twin and earth, however im slightly worried by the max amp rating of 1.8 amp for the 0.6 solid core wire as i am not sure how much current goes through this track. Would i not be better using say 3 amp stranded wire?.

    2. I would like to ground the heatsinks to avoid the need for the micah washers to isolate the driver chips agsinst the heatsink. However is this simply a case of grounding the mounting bolt of each heatsink to the case via maybe one of the standoffs on the corner of the pcb?. Or ground it to where the incoming earth is grounded to the case? Or is it more complicated than that?. Grounding seems to be a bit of a dark art reading about it on some threads.

    3. I want to check the wiring from the db9 to the stepper motor as suggested for a short or breaks etc, is there a method for doing this, i have a multimeter but ive not much idea how to use it other than the continuity test.

    Thanks
    Adam
    Last edited by howser37; 07-02-2017 at 02:28 AM. Reason: Added Content

  6. #36
    GND's Avatar
    Lives in Cambridge, United Kingdom. Last Activity: 3 Weeks Ago Has been a member for 2-3 years. Has a total post count of 60. Received thanks 2 times, giving thanks to others 11 times.
    Hi Adam,

    To answer your questions;

    1. I had suggested solid core wire simply because it is easier to work with on the back of a pcb, but your concerns about ratings are legitimate, and so I'd say try the stranded wire and see how you get on. Strip the ends, twist the strands together, and then tin them before you try soldering to the board. Sometimes stripping a bit overlength is good, so that once tinned you can trim them right back to something that will neatly sit on the PCB pad. All you need is a couple of mm exposed at each end ideally for the actual repair.

    2. Grounding is a whole subject in itself! In simple terms, the issue is that wires and connections aren't perfect, and don't have zero resistance. Hence although you might connect things together to form a common ground, there are always tiny differences in voltage across them. This is especially the case when large currents are involved, of if there are multiple paths between the grounded items. And since ground is your reference for everything, then this can cause issues in operation. Hence care has to be taken as to how you handle grounds, and that is why it's a big deal. In your case, I know the mica washers are a pain, but the original designers specified them for a reason. I'd be reluctant to change things and ground the heatsinks, even if it looked like it should be possible. With a system that is already a bit unreliable, I think such a change would be very unwise.

    3. I guess we're looking for short and open circuits on the interconnections to the motor. So, to check for open circuits, put the meter into "Ohms" mode, and select a low resistance range (if ranges are selectable!). Disconnect the motor, and probe each end of the cable assembly on matching pins, and check that the reading is low - ie. there is a connection. Should be one or two ohms max. I'd also flex the cable when doing this - although that might need three hands! - to make sure there isn't an intermittent fault. Try and test as much of the connection as you can, so start on the PCB at one end, and finish at the motor connections themselves if at all possible. Access to connections may however be limited, so you may need to compromise this, but the closer to the PCB and motor you can test, the more of the system you are actually checking.

    Open circuits - ie. broken connections - are one thing, but since you are blowing your chips, the short circuits are the more likely culprit, as these are more likely to cause large currents to flow. So you have to try and find where your motor wires are shorting to. Here you should again disconnect the motor (to avoid its low resistance coils giving you false readings) and then pick a motor drive pin and apply one of your meter probes. Then touch the other probe onto each of the other motor wires in turn. You should not see very low resistance readings, otherwise it indicates a short circuit. Again flex the cable when doing this, especially near the connectors, as the fault is likely intermittent. If all are OK, move onto another pin, checking if it is shorting to any of the others. If the cable is still connected to the PCB, you may get erroneous readings due to the driver components, which sit across the motor connections - especially protection diodes - so you may have to just check the cable itself, totally disconnected. See how it goes....

    Hope that helps!
    Graeme

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  8. #37
    Looks to me like that track had a problem, someone tried to fix it by gobbing solder over it, found the solder wouldn't bridge the gap until some of the tin had boiled out of it, so he delayed and destroyed the glue holding the track down to the PCB.

    After 30+ years soldering for a living I could fix that in a jiffy. OTOH I can remember what it was like when I started so I feel your pain

  9. #38
    Thanks Graeme. Much apreciated. I read a few things about the mica washers not being as effective at getting the heat into the sink, hence the idea of just having the thermal compound. But you are right i will not start messing with things like the grounding in a system that i already dont trust lol. Thanks for the info on testing the wires, im pretty good with mechanical things but electronics baffles me at the moment.

    Hi Robin, thanks for the input. You know now that you say it i dont know why this didnt occur to me that this looked like a previous repair. But it does look like a soldered over track and the solder gas blown, but again i guess its back to what caused the first failure.

    Anyway i will report back what happens

  10. #39
    Hi guys just a quick update and a query, i have cut away the broken track as suggested and eventually after a bit of trial and error have managed to solder a jumper nicely to the right terminals on the back of the pcb, quite a task as the pins are very close together :-o. replaced the IC chip and also upgraded the cooling by having a much beefier fan suspended from the top of the contol box onto the Driver chips and heatsink while i was at it.

    I am now checking the wiring on the suspect X axis motor, i have attached a picture to show what i am dealing with, i want access to these termianals but they are burried inside these 3M terminal blocks, i popped one out and the brown driver wire literally just fell off whereas the other two needed a bit of removal force, so i guess even that brown wire could be a potential short. To be honest im not too impressed with these 3M terminals, they seem a bit fiddly and precarious, what kind of terminal are you guys using for this, wouldnt something i can get a tester on at a later date without having to rip the thing apart be more suitable ?. Id like to remove them all to test the cable and replace them with something a bit less permanent and more robust if possible

    Click image for larger version. 

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    Last edited by howser37; 08-02-2017 at 04:30 PM.

  11. #40
    GND's Avatar
    Lives in Cambridge, United Kingdom. Last Activity: 3 Weeks Ago Has been a member for 2-3 years. Has a total post count of 60. Received thanks 2 times, giving thanks to others 11 times.
    Not sure the picture got attached. Interested to see what you're dealing with before offering suggestions.....

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