Hi,
a lot of damage could have been done putting 400V plus on a 220V machine. Commonly electronic devices have MOS varistors at the input, and while they smoke up and go bang, they
often protect stuff downstream, so you might get lucky and find not too much wrong,....BUT all the electronics could be toast to. Not really anyway to tell short of pulling it to bits.
I'm not familiar with the make and model of the machine. Lets imagine for instance that ALL the electronics are toast then ask yourself.... 'are the mechanical parts of the machine in good enough order
to command the asking price?'
With a machine of that age it is highly likely that you would have to up-date the controller, possibly the servos and other electronics anyway. There are plenty of posts on this forum
of guys whom have bought a good (mechanically) machine but have to provide a complete set of controls/electronics. Its not a cheap or easy exercise, but most end up with
outstandingly good machines at a small fraction of trying to but new or even secondhand in working condition.
Just as a pure ball park figure, lets say that you buy a controller solution like Mach4/ESS, or UC300/UCCNC, or a Centroid Acorn, or LinuxCNC/Mesa.....and you had to buy
three new servos and drives, you could spend anywhere from $1500 to $3000.
Now ask yourself...'is this machine investment what I wanted and does it represent good value to me for $4000 for the machine and another $3000 to get it going really well?'.
Craig