Help with Problem X axis Stepper Please

[GND]

Can't really add much over John's useful suggestions. It seems clear now that there is a fault beyond the chip - this second failure suggests the first chip didn't just expire for no reason. So checking for decent connectivity to each physical pin using a multimeter could be worthwhile. Ideally right to the motor connections, and to the other connected components on the board. Maybe an intermittent fault though, like a cracked PCB track, which may measure fine most of the time, but open up as things get warm.

Maybe it is time to get new electronics as you say? Particularly if the risk of failure is costly to you. I hate to waste perfectly serviceable kit, but sometimes pragmatism has to take over!

Cheers
Graeme

[howser37]

Hi Graeme, im pretty much resigned to the fact im going to build a new control box now, i do intend to build a new CNC myself at some point so it makes sense to get learning now and also i may well overspec it so that i can use it with my new machine when i get it built.

In the mean time i am wondering if it would be as simple as possibly utilising the spare driver in this control box as the second X axis driver, as there is a 4th axis driver in the box that is not being utilised as i do not have a rotary axis, not quite sure what would need to be changed in terms of settings as the other 4 drivers are on one board and the rotary is on a seperate board

[howser37]

Think i have found the likely culprit, looks like a cracked track on the back of the pcb, i will post a picture up

[GND]

Sounds promising!!

[howser37]

Here is the picture of the cracked track, is this repairable?. Definitely seems to be the culprit as it is on the correct chip and even leading to the correct area of the chip that has popped both times.

[GND]

Definitely repairable! I'd suggest you cut out that offending length of burnt track so it's not flapping around in the breeze, and then re-make the connection with a short length of thin solid core insulated wire. You're lucky in that it essentially connects two of the chip pins together, so you can use the PCB pads for those pins as end points on which to solder your little wire. Pull the chip out and d the work. Given a few minutes with the chip datasheet we could also work out which pin has become disconnected, and hence what the possible issue might be.

Now of course it could be that the track got burned out as the chip failed, and hence wasn't the cause of the failure - but more the result. Or indeed, has the chip actually failed? Could the board have failed whilst the chip is still OK? Looks like that track took a bit of an overload, but why is that?

Datasheet, datasheet....

[howser37]

Thanks Graeme, i will see if i can find the data sheet online.

I would say both chips have definately failed, the black plastic has popped in both cases and in the case of this particular chip i opened up the contol box fairly quickly and the place where it had popped was still melted and gooey. But like you say whether this failure resulted in blowing the track or wwhether the track blew as a result is a different matter. I will admit i was not particularly thorough last time i replaced the chip in checking the back of the pcb, i just tested the socket pins were gripping ok and only quickly scanned the back so it is possible that this crack was there prior to replacing the chip.

This failure did take out an 8 amp slow blow fuse on the power supply too

[GND]

OK, so a quick look at the datasheet suggests that the "disconnected" pin is pin 15, and that it is normally connected to pin 24. This makes sense and these are the two main voltage supply inputs for the motor drive stages. Hence if one of the motor windings was taking too much current, that thin track could fail. Looks a bit thin to me for a motor supply line? Designed to take an amp or two? Hence maybe it simply burned out and effectively disconnected the motor? Worth a repair and a retest?

[GND]

OK, just seen your latest email - scrub the retest! New chip required, but the question is - why did it fail? The motor must be taking too much current at some stage thus blowing the chip and in this case taking the voltage rail track out too, a bit like a fuse. I suspect it must have been intact last time or your repair would not have worked. Hence I think this is a symptom of the latest failure rather than its cause.

I think I'd be checking my motor wiring for issues, because if there is a problem there, you'd potentially end up blowing whatever you connect - new drivers for example - until that is fixed!