G201 death/repair/questions/problems (long post)

Hi folks,

Chris Brick here (aka resosys).

I've got to be doing something wrong. Really wrong. I'm hoping someone
here can help out as I've exhausted my knowledge of these systems and
I'm still having major issues. This is probably going to get pretty
long so I'll apologize now.

Machine:

Layout: 2 axis plasma cutting table
Motors: SloSyn triple stack 260oz/in 4-wire
Drive: X is dual belts on a shaft, Y is single belt on gantry

Interface/power supply:

Stepper controllers: Gecko G201 (old style, no covers)
Parallel Interface: Axxus Technologies board
Transformer: Toroidal, rectified output is 56-57V DC
Capacitor: 10,000uF (too small?)

Software:

Currently running TurboCNC for calibration/initial shakedown but will be
moving to EMC once I get things up and find a PC for it.

Last Saturday I got the machine up and running with two known working
and new G201s (one borrowed, ughhh). I was calibrating the software and
bringing up the limit and home switches. I turned the stepper power
supply off and walked away from the machine for 10 minutes. Nothing was
touched, moved, unplugged, etc... When I turned the power supply back
on, poof, smoke out of the G201s. I pulled the heatsink plate off of
one of them to find the same mosfets had died as my other two Geckos.
My heart sank, I packed up my things and went home to consume some ice
cold beers.

Questions/thoughts:

I've got the motors set to 3amps via the current set resistor.

I don't have any fuses between the G201s and the power supply. I was
under the impression that this wasn't necessary but will install them if
it will help. Any thoughts?

I only have 10,000uF of capacitor on the power supply. When I built the
supply a year ago, I remember doing the math to make sure it was within
the specs in the Gecko literature. Will a high ripple voltage cause
damage to the Geckos?

I do not have the disable pin connected on the G201s. Is this something
that should be pulled to ground until everything is powered up and I'm
ready to move motors? I was planning to do this but haven't yet.

Voltage spikes? I've done tests with my power supply that suggest there
are no spikes when it is switched on. Any thoughts?

Is there a correct power up sequence? I've been leaving my parallel
port connected and the software running while only turning off the power
supply/Geckos/motors.

I'm hoping someone has seen this or a similar issue and can help me find
the problem prior to me making more smoke.

Now on to repairing the Geckos. (Thanks tons to those of you that
helped out last week when I posted)

I sent an email to support@... but haven't received a
response yet. I don't expect it either since these units are out of
warranty and it appears I'm doing something wrong since I killed a bunch
of them.

Last week I posted about letting the magic smoke out of 2 of my G201s.
I did some surgery on one of them this weekend and got it back to
partial health. One of the phases is still acting odd. I only had
IRF530N power mosfets on hand and only enough to replace the parts that
tested bad. I've ordered more IRF530's and some resistors. Some
questions here:

I've been led to believe IRF530N and IRF530 fets are interchangeable.
Any wisdom here?

Is there an easy way to test the mosfets in circuit? I've got a nice
Fluke meter that does diode testing. (If not, I'll replace them all)

When running the partially repaired G201, the red LED flashes and the
motor is jumpy as if one phase won't swap polarity. Has anyone seen
this behavior before?

Should the reddish-brown capacitor be replaced when the .5ohm 3watt
resistors go?

My meter reads .2 ohms on the resistors so I'll replace them.

Are there any tests I can do on the motors that will tell me if they
have problems?

When things were running, the system was working well. The axes were
smooth, turbocnc's pulse train was smooth, calibration was going well,
and I was happy and so close to making my first cut. It will happen
soon.

Thanks for reading my long winded post and for any wisdom you may have
that will help me get things fixed/solved/running.

Chris