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

I am repairing a CNC machine at my high school.

It has toroidal trasformer with 3 isolated 28.5VAC windings.

It is a 3 axis XYZ machine with each axis controlled by a 4.6A stepping/synchronous motor.

It is connected to a PC running LinuxCNC via a parallelport and PMDX-122 breakout board.

The machine works, but the original 30-year-old stepper drivers are all totally broken.

I bought some DM860H and DM556 drivers off Ebay and Aliexpress, respectively; they worked, but have no flyback diodes.

I accidentally broke all of them.

I ordered 1 new DM860 from Aliexpress.

Should I just suck it up and buy good, genuine drives for the remaining axes?

All the axes?

I can make a rectifier, if needed.

What brands are good?

I am reluctant to spend like $300 ($435 in Canada, where both the machine and I reside).

Canada's potential future retaliatory tarrifs on USA in response to Trump's potential future tarrifs on Canada might affect stuff too.

The computer works fine, so does everything else, all I need is stepper drivers at this point (I need 1-2 THK LM guides for th Z axis, but that's a problem for future me).

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.

No blown cap.

Also, one DM860H managed to work fine after the fuse blew.

They really don't have any flyback diodes, I assure you.

And the transistors ain't DMOS either.

The DM860H drivers have their own rectifier.

They accept AC.

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".

Oh.

I thought only DMOS had internal diodes.

Now I know.

Thanks!

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)