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

Any clue why adding fast diodes would cause them to blow up?

What replacements did you buy?

Any recommendations?

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

tommylight wrote:

langdons wrote:

Any clue why adding fast diodes would cause them to blow up?

IT WILL NOT!
Unless you reverse polarity.
I wonder where are you getting such wrong info from and why are you so stuck at diodes ...
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Are you aware that miss wiring the stepper motor will blow the drive?
The "fuses" you mention, are NOT fuses, they are resistors used for current limiting in the drives.
Also mentioned before, do NOT cut the drive power on the DC side, ever, meaning, if you wire the drive and motor and use any power supply that is already powered, then touch/wire the DC power to the drives = they are dead in most cases.
 

When I say fuse, I definitely mean fuse.

A 10A SMD fuse, to be exact.