"PrecisionmachinisT" wrote in message
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"Ignoramus5734" wrote in message
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On 2010-08-29, Jon Elson wrote:
Ignoramus5734 wrote:
Since yesterday, I had the Z axis behaving very weirdly, suddenly
lots
of chatter and vibration, extremely erratic behavior, then no motion
at all, then some motion etc.

Attempting to diagnose it (isolate the issue) pointed to a servo
drive.

Since I have several additional drives on the shelf (they were
cheap),
I swapped one for another. Now the Z axis is back to working. I
opened
up the drive that I relpaced and saw one chip blackened.

Not sure what to make of this.

i

Whose servo amp? Can you tell by location what that chip is connected
to?
Check another to get the part number of the burned chip.

That was am AMC 30A8 amplifier, revision T.

The chips on them mostly do not have markings, this one was a small
one in the middle of the motherboard.

I really like the drives, their simplicity, cost and support from
AMC. I do not know if I can guess the cause. But, possibly,
interference again is to blame. I have, since, routed the twisted DC
motor cables away from control stuff.

You mentioned ferrite cores to place on these cables. Would you
suggest any particular Digikey part number?


Its a garden variety 15-30 brush amp which when reduced to basic specs are
about as common as dirt.

The 30amp peak spec is probly wishful thinking--at the least it's gross
overkill for a bridgeport sized mill

--personally I would look at the "copley controls" and / or servo dynamics
offerings on ebay....most likely you are running in velocity mode (ie it
has
a tach feedback dedicated to velocity control as well as having resolver
or
encoder for on-the-fly and final-in-position check/ verify ) and so
suggest
make sure there is an actual pot to adjust your tach gain because
sometimes
a fixed resistor is substituted where some OEM has dedicated to a specific
motor for instance glentec which used 7 volts per KRPM but the tach output
on your particular motors might well completely out of that ballpark hence
the additional dash numbers ( revisions )

1525 brush amps are pretty near a dime a dozen these days--invest a little
time in research and you can be an expert it's not ****ing rocket science.


One other thing....

The amps which spec out as using an AC 110 input are also fair game here
because they are basically your standard DC input unit except they also have
an additional power supply which is typically built-in to the upper sheet
metal heat sink cover.

--remove said cover, detach the leads from the barrier strip and toss--now,
attach the red and black from YOUR existing DC power suppy buss to the amp
instead and all is good so long as your existing supply output is 140 dc or
less.

--