LB-10 blowing spindle drive modules left and right

[GITRDUN]

My brother has an early to mid 90's LB-10 that keeps blowing the drive modules on the spindle drive board. They replaced all the modules, it lasted maybe a couple hours before it happened again. So he bought a used drive board and it ran for about 10 hours before it blew the modules on the used board.
When the modules are replaced the spindle runs smooth as can be and stops perfectly. Had a CNC service tech check the machine out and he couldnt find anything wrong while it was running the day before it blew them the last time.

Anyone have an idea what could be causing this? Is the spindle motor itself in need of repair? If so wouldnt it show some obvious problems while ramping up and down or stopping? Could incoming voltage spikes cause this sort of issue?

[underthetire]

Is it the fanuc spindle drive or an okuma vac drive? Was the motor checked with a megger? Is there a transformer on the incoming power?

[GITRDUN]

It does not have the okuma VAC drive, its the old Fanuc drive. No the motor was not checked as far as i know. I think the incoming power does come from a transformer outside, electrics arent my thing so i might be mistaken.

Funny thing is he has another mid 90's Okuma LB15 that is down right now due to the exact same problem. It has also blown the spindle drive modules twice. They are both running from the same incoming power lines. This is why we suspect voltage problems but have no way to verify. We also have 2 other Okuma lathes of similar year and model running from the same power source and they run like clockwork.

[underthetire]

All i can do is give you suggestions here. You absolutely need to mega ohm the motor. Buy one, get a service tech in, whatever. The meter I use is only about 150 bucks and works great.
Megohmmeter - Megohmmeters - Electrical Power Testing - 3T105 : Grainger Industrial Supply

The other thing, when you replace modules on the fanuc drives, you should change them all IMO, and replace the top controller board. The top board controls the transistors, so if it's not acting correctly, it will blow them. I usually bring Fanuc in to repair those on site. I have gotten 4 in a row bad ones from Okumas re builder in the past, then had Fanuc come in. He had the machine running in about an hour, and as far as i know it still is.

[Algirdas]

could be a lot of causes.
See for protection device - ask Schneider, telemecanique, Merlin Gerin, GE, ABB or Moeller - all of theml have it. You need to be sure about all power supply phases are correct - no jumps no holes.
No need for some special monitor - take a simple one, relay based. Ir alarms when one phase is missing or some significant phase voltage disbalance. That's enough.
Replacement of all power modules is good idea, because drive unit is capable to work almost well with a couple of power modules broken out of 12 of them.
Control board, however, no need to replace so often. It's easy to check if control board is good or not.