One of my CNC machines has a circuit board that has failed 3 times
now. The control is a FANUC 3T. It is an older control so failing
boards don't surprise me. But it is just the one board. This board has
many custom hybrid ICs, some other of the shelf ones, 6 EPROMs, and
one electrolytic capacitor. I have checked this cap on two boards with
my meter and the cap has the stated value and is not shorted. But I
don't have a way to check ESR.
The failure mode for all the boards is the same. First the turret
on this lathe will occasionally index in the wrong direction. After
the machine is powered up for a while it will then start to index
properly. I can control the turret rotation from a program but when
the board starts to fail it will only index in one direction.
Furthermore, then turret should always rotate in the direction that
is the shortest to the next tool called up, but when the board starts
going bad the turret still only indexes in one direction.
Unfortunately this is the wrong direction.
After this failure other things start going wrong, like the speed
control. Changing the boards has always fixed the problem. Note that
when I change the boards I have to swap all the EPROMs so that the
programming for the machine operation will be the same.
Since all the boards seem to fail the same way I was wondering if
somehow a failing cap could cause this failure. Even though the cap
value reads fine with my VOM, that does not measure ESR.
In any case I'm gonna order some caps and see if anything changes
but I would like to know if it is probably gonna be a waste of time.
Thanks,
Eric