Should I just suck it up and buy a good stepper driver?

All modern step motor drives have flyback diodes, what they typically do not have is an overvoltage clamp.
This means you must never switch the DC power to the drives anywhere between the power supplies output
capacitor and the drive itself. This means no switches/relays/fuses/circuits breakers in the DC circuit. The
fuse in the  drive itself is just for fire protection, if it blows, the drive was already dead.

All standard MOSFETs have inherent "body" diodes which will function as flybacks
though typically Schottky diodes are added to reduce voltage drop and hence power
dissipation.

Been reading this for while, I think you need to reassess what you think you know compared to what you actually know.
Usually the stepper drivers are pretty hardy, the ones I have in my mill are about 15 years old and haven't missed a beat.
I've never heard of anyone having to make modifications.
Some of the early TB6600 drivers weren't as reliable as they should have been, no experience with them myself but many reports of them being that way.
So just settle down, do things the recommended way and don't try to modify things that don't require modification. And if you still insist of doing board level mods consult the data sheets for the components that will be affected. I'm sure this would have resolved the issue of "no flyback diodes".

unknown wrote:

Been reading this for while, I think you need to reassess what you think you know compared to what you actually know.
Usually the stepper drivers are pretty hardy, the ones I have in my mill are about 15 years old and haven't missed a beat.
I've never heard of anyone having to make modifications.
Some of the early TB6600 drivers weren't as reliable as they should have been, no experience with them myself but many reports of them being that way.
So just settle down, do things the recommended way and don't try to modify things that don't require modification. And if you still insist of doing board level mods consult the data sheets for the components that will be affected. I'm sure this would have resolved the issue of "no flyback diodes".

 
I bought two 2nd hand machines with stepper system. They were pre configured for 4 axis, so I had some spares to kill. Out of the 8 drivers two or three are still working. (so I would say occasional death happens)
At least one or two I probably finished by creating a short when I was "repairing" the machines long time ago.
My guess is that the drivers were running at their limit for a long time and were a little undersized for the motors. (or can something age inside?)
The last year drivers started quitting service one by one. First by making some humming noises during machine start, then eventually stopped working.
Given the prices of new ones, not worth investigating. (but we are still talking 10-15 years, before failure)

Goto the gecko drive home page, they have some great stuff about stepper motors and drivers, and it's broader than just their own products
After becoming wiser pick drivers that match your motors, don't guess.
Carefully set one axis up, don't take any shortcuts or do anything additional you think is right, this would seem how you got into this mess.
The drivers are going to come from china, probably the same factory, only thing that may change is the silk screen on the front cover.
I've bought from stepper online, sellers from eBay and from aliexpress, no issues as long as you take care as would with any other job.
Do one axis at a time, thereby only having to debug one axis, wire the rest up the way you do the first one once it's works and you'll be fine.
Spend time doing research, you'll be wiser for it, you'll do a better job, you'll stop wasting money.
And for crying out loud keep your soldering iron away from the drivers.
If there is an area you are not totally grounded in get an expert in and don't suggest to them how to do their job.

What caused the original failures ?
Are the existing motors good or are they the cause of the initial failures ?
I've lost count of how many times a tech has replaced the failed component is a system, not investigated why it went only to destroy the custom ASIC they just replaced.

tommylight wrote:

HEXFET, TrenchFET, Epitaxial FET, .... damn i am getting old and this time i am not blaming it on being 3:15AM right now, there are many more types of MOSFET's, and almost all have flyback diodes, you can spend days sifting through catalogs to find any that does not

 

I have been making servo amps since about 2004, and had some issues with them blowing up under certain conditions.  I used some beefy 56 A International Rectifier HEXFETs.  Using a digital scope, I was horrified to see that the body diodes in these transistors did not start to conduct until about 10 us after they were forward biased by up to 12 V!  So, I had to add in some ultra-fast diodes across the transistors to prevent this.  The issue was that when the high-side transistor was sourcing current and then shut off, motor and filter inductance would pull the source of that upper transistor down to large negative voltages, and cause the gate driver chip to turn both transistors on at the same time, leading to fireworks.  The  extra diodes solved this issue.
Jon