7i76e damaged driver output

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19 Jan 2022 18:03 #232459 by Jalapeno56
This is my 2nd board with a damaged driver output(s). Verified by no voltage between STEP+ and DIR+ (Linuxcnc not running).
I have followed norberts connection sheet and verified my connections multiple times.  There is no switch between my 24v power supply and the 7i76e.  There is no voltage back-feeding from my stepper drivers. 7i76e is grounded by the mount hole close to the RJ45 connector.
Is there anything ya'll can think of that I may be doing to create this problem?

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19 Jan 2022 22:50 #232489 by PCW
Replied by PCW on topic 7i76e damaged driver output
No voltage between Step+ and Dir+ is expected when LinuxCNC
is not running.

You should see 5V between Step+ and Step- and 5V between
DIr+ and Dir- when LlinuxCNC is not running.

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20 Jan 2022 21:22 #232553 by Jalapeno56
Either way, I have no voltage coming out and i cannot get any of my steppers to move.

Thanks

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20 Jan 2022 21:29 #232554 by PCW
Replied by PCW on topic 7i76e damaged driver output
Do you have 5V between Pins 6 and 1 on TB2?

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20 Jan 2022 22:50 #232564 by Jalapeno56
Yes, I did. I also hooked up dir+ and step+ to 5v and still no movement. My drivers seem to be working, green lights and steppers locked. I already sent this board and another that had a short between Tb1 pins 5 and 8 back to mesa for repairs. Should arrive at your facility Friday.

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22 Jan 2022 00:05 #232712 by Jalapeno56
Did some more testing today...
Checking my power supply at start-up I am showing a spike of 27.32v, above 24v for 3.2 microseconds and leveling out at 23.96v. Current is peaking at 497.43 amps, leveling out within 4.3 microseconds at 23.89 amps.
I am hooked up to a known 1 ohm load (0.9994 actual).
CVR value is .0549 ohms for current
Standard voltage tap
Scope settings are:
Acquisition: 10Ghz, 20 million points
Ch1: voltage =3.5v
Offset =10.5v
Attn= 13.214 :1 (as-read)
Ch2: current =250mv
Offset =750mv
Attn= 2.016:1 (as-read)

My question is, Could this spike be whats causing my issue? I sent back my boards back to mesa for repair and now I don't know the values on the power side of a 7I76e to be able to determine if this is the culprit. I double checked all connections and ran this test multiple times with the similar results.

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22 Jan 2022 00:41 #232713 by tommylight
The numbers do not add up:
the voltage seems ok, 27V should still be well within limits of Mesa board
the current is not ok, or the voltage is not ok, as both can be an issue.
If the current through a 1 Ohm resistor got up to over 400A , that means the voltage had to be 400V at some point, inside those microseconds.
Either way, i would not use that power supply for anything at all, maybe running an incandescent bulb ....

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22 Jan 2022 00:56 #232715 by ALittleOffTheRails
Maybe not tommy.

To avoid turning a resistor into smoke you would be looking at something like a 570 odd watt resistor min.

Now if it is a wirewound resistance, it might be seen as an inductive load to begin with.
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22 Jan 2022 00:56 #232716 by PCW
Replied by PCW on topic 7i76e damaged driver output
Just got your cards:

Card 1: Shorted field power
TVS DIODE CR15 shorted
This likely means the >32V was applied to the field power
or field power was applied backwards (cards are tested at 31.5V)

Card 2: No Step/Dir outputs
No Problem found, all Step/Diir outputs within spec

(Most common cause of lack motion of step/dir drives is too short step times)
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22 Jan 2022 01:30 #232719 by Jalapeno56
But shouldn't my scope see the pulses from the card? Maybe my record time was too short to see them. What is the (G)(M)(K)hz output on the card? or is that dependent on my settings in Linuxcnc?

2nd or 4th question: Im looking at a Meanwell 24v(max) 14.6 amp power supply. My current power supply is a 36v 16.2 amp turned down to 24v. I know that most of these power supplies lose current at higher voltages. Is the Meanwell a good choice or should i still look at a larger supply turned down to maintain current capability?

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