RE: [CAD_CAM_EDM_DRO] Gecko failure/repair

You are probably right that you blew one of more of the 8 IRF540's.
Usually you can find the bad side two ways. The first way is the what
you did. You can verify it by using a vom set to the lowest scale across
the mosfet leads. A shorted condition will generally be seen if bad.
Compare the results with the good side of the H bridge.
I have replaced them in the past on both the G201's and the G320. You
need a good soldering iron to heat up the leads and desolder them.
Remember that is a multi layer board when pushing out the mosfet leads.
Also check the .05 ohm 3 watt sense resistors
If the unit was still installed, I use a VOM set to read the appropriate
power supply voltage across A and B on the Gecko without the motor
connected. With it powered up single step it 10 times at a rate of one
step per second. You should see the voltage change with each step and
the reading read on a 36VDC power supply will change from +36 after
several more steps to -36. That would indicate the step and the output
is correct. Then connect the volt meter across terminal C and D and
repeat the test. The output will probably be the same if the fets were
good. If either AB or CD read zero then that is the bad side and you
should be able to locate the bad fets using the VOM test.
I also use this swing test on ALL drives before connecting any stepper
motor. It is cheap insurance that there isn't a problem in the drives
and since there is no load at this time the chances for a disater is
reduced and if there is a problem it can be fixed without releasing the
smoke in the fets
The cause of the failure could be caused by several things. You said
you may have had a short across the pins which would do it or a loose
connection could have caused an inductive spike to blow it.
Dan

-----Original Message-----
From: resosys [mailto:resosys@...]
Sent: Wednesday, March 26, 2003 11:14 AM
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: [CAD_CAM_EDM_DRO] Gecko failure/repair


Greetings,

I'm hoping someone has some wisdom on a particular problem that's
developed with one of my old style Gecko 201 stepper controllers.

Symptoms:

The motor vibrates back and forth as if one of the phases is not
working. Replacing the stepper controller with the other axis'
controller results in proper operation (motor and wiring are correct).
The "failed" Gecko powers up and responds to step and direction signals.

It seems as though one phase output was blown. There are no burn marks
or blown parts on the top of the board that I can see. Since these are
the open case selloff units with no warranty, I removed the
heatsink/mounting plate and examined the drive FETS. One of them next
to the mounting screws shows a slight burn mark on the leads.

It may be possible that my motor leads shorted and popped the output for
that phase since I found a loose wire on one of the pins on my motor
connector.

Questions:

Has anyone seen this behavior?
Are there any specific tests to perform?

I have the parts here to repair the unit, if it's possible. I'm hoping
someone has seen this issue before and can tell me what damage was done
so I can get a head start on troublshooting and repair.

Thanks in advance for any help.

Chris


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