We have a second drive that created the same problem as a drive of
the same model but smaller in size we tost out 3 years due to a
"SC" error "Short circuit" as you place the drive in RUN mode.

This time, I would like to repair this one instead of tossing it.
I can't remember the exact model # at the moment, a 5xx something
VF drive.
what I have found is, the 2 DC bus caps "2000 uf, 400 VDC" only test
up to only ~1500 uf each. I really don't think this would be the cause
if the "SC" error in run mode. This error takes place with no delay even
before the drive would normally ramp up. Nothing is apparently shorted.

I did find how ever, on the optical isolated Gate driving circuit one
bad CAP "58 uf, 35VDC" which measures ~ 1 uf on the first phase, the
same caps in the phase 2 and 3 circuit measure around 35 uf and appears
to have leaked out fluid a bit over the SMT driving trannies.
The bad cap I found how ever does not appear to have leaked at all.
So confusion tells me to replace all of them to start with.

Any ways, I applied voltage to the IGBT bridge and there isn't any
shorts even thought the CPU thinks there is so, I have drawn a
conclusion that maybe the gate firing driver circuit has fail and thus
the loop back monitoring isolation circuit isn't detecting a feed back
response due to the bad driving circuit not signaling the bridge on that
one leg and assuming a short..

Does this sound like a plausible train of thought ?

P.S.
I'm doing this with out a service print, it does not seem like its to
difficult to resolve this problem.


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