Denford Software & Machines

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This happened on my Baldor board. I replaced the blown drive chip and it happened again. I checked all over the board and could not find anything that looked bad. I called Denford USA about sending the board in and a guy from Denford UK called but i missed the call and hadnt had time to call back. What would cause a drive chip to blow? Its not the machine since I had another balor card and it ran with it.

It could be anything that caused the chip to blow, after you replaced the faulty chip did you try powering up without the stepper motors not conected? if not it could be the steper motor / wiring that is causing the chip to blow.

As he had another Baldor card working fine, then it can't be an issue with the motors or wiring...

I would guess that something further up in the stepper circuit is faulty and allowing a high current (or short) in the driver chip - eg, a faulty diode ?
Steve should have a better idea as he knows how the circuit works...

I do have another Baldor card and the machine is working. If I knew what path or paths I need to check and what to look for I could replace whatever is faulty.

The Circuit in the Stepper drive is a simple L297 and L298 stepper circuit.

The driver chip sends signals to the output stage which then connects the motor windings.

Current is controlled by a sensing resistor. The resistance and inductance of the motor winding slow the speed at which the motor current rises.

If a motor winding is shorted out (a faulty motor or trapped leads or short to earth) then the control circuit will not be fast enough to protect damage to the output stage of the unit and the chip will blow up.

Also if the chip overheats (not enough thermal compound under it or the securing screw not tight enough) then this can also caus the device to fail.

They also sometimes just fail.

Hope this helps.

See the attached link for information on the circuit.


https://www.st.com/stonline/books/pdf/docs/1734.pdf

For each stepper driver, they are two resistors and 8 capacitors?. Where can I get the capacitors at?

Try RS components or Farnell.

We dont build these so do not know the exact parts.

Unless there is visible damage to these parts I doubt they would be the problem. I would check the diodes 8 each drive.

Steve wrote:
See the attached link for information on the circuit.


https://www.st.com/stonline/books/pdf/docs/1734.pdf

Bad Link any hope in finding a good one?

Hi I atach a scan of the Technical data sheet manual.

This is a really good resourse and explains how stepper motors work.

Check capacitors? How old is board? I had two go dead short, tiny decoupling caps from V to ground.

Tom