help- stepper drive question.

[jmytyk]

I have 3 drives that show if I put one meter probe to the Powersupply Ground, and the other probe to the Aluminum shell that is the drive 'body' (not the metal case the drive is normally in, the drive is sitting on a wooden table) it will complete a circuit. -

this really doesn't seem right?? is something blown up inside the drive?
thanks
jon

[jmytyk]

anything??? here is another question, do you guys have your stepper drives isolated from the box they are contained in? - let's use geckos for example- many i've seen are mounted to a heatsink. in my case that heat sink would become electrically hot - at 50volts (that's what my PS is) it doesnt seem right. the drives are made by Centent, they are either 0142, 0143... thanks

[corollaman01]

The mosfets in the case are probably using the case for heat dissipation.
If they are blown they may be shorting to the case. If this is the case you will need to find the blown ones and replace them. Have you isolated your motors from the frame of your machine? If not you should as this is one way the drives can be damaged.

[jmytyk]

thanks for the reply.

currently the drives are sitting on the table, they aren't connected to anything- i was trying to source out the problem, and hopefully not blow anything up.

so the bad news to me is- the drives i have are in cased in Epoxy ( i think) so working on them might not be an option- any ideas? they are Centent drives- old cousins to gecko's - as Mariss mentioned he worked on the design

when i did have things all plugged together in the machine - everything is wood- so likely they were isolated.

[jmytyk]

an update: i took everything apart, and bench tested one of the drives. it works, but not very well. it is likely software.

when i am in the motor tuning page, the motor resonates badly- unless the accel and speed are maxed - but still it doesn't work so well...

but after i left the shop -i did some research and I found the steps / units are way off- 1000, versus 20k

so hopefully that will be the problem.

are there any other symptoms of a blown MOSFET?

[jmytyk]

ok, update again. the pulse per unit- not the problem. :-( it's set at 20k.

I was using mach 2, now i installed mach 3, no need to waste time on something i was going to upgrade to anyway.

i've messed with the uS for step and direction, not really helping much- they are set to 5uS

i've tried a bunch of different combo's of speed and accel. nothing yet works so well.

would making a video of this be more helpful?

so, any ideas?

thanks.

[H500]

If a fet is blown, the steps would be uneven. The motor might even step backwards in some positions.

[jmytyk]

H500, you're right on. Visibly fried transistors in each drive. even worse, the drives were encased in epoxy- so no hope of fixing them. a bit of destructive searching clearly showed the drives and what was wrong with them.... here is some background info.

expensive mistake in the wiring department on my part.

posts 17-21
Geckodrive user input requested