[PMT2000]

I have been trying to figure out a problem with the servo drive in an Okuma LB 15. I has the Alarm 201-4 Z Axis Servo Amp 2E6. The LED on the Z axis servo amp for IOC-S is lit (Excessive current flow through transistor bridge - short, according to the maintenance book - oh boy, that tells me a lot.)The BL-D 50 servo amp was sent in and rebuilt on the advice of the repair tech. No change. I tried switching the X and Z servo amps and the alarm stayed on the Z axis and the same LED was lit. Servo amp ruled out as problem? I accessed the electrical connections at the Z axis servo motor and took resistance readings and compared them to the X axis servo. I also checked for continuity to ground and got the same thing on both. After studying the schematic, the only thing that draws current through the transistor bridge is the servo motor. Maybe it has a short that only shows when power is applied? I'm just wondering if any one else has encountered the same thing and what the fix was. Thanks.

[underthetire]

Do you have a mega ohmer? Time to properly check the cable and motor to ground. I've also had the motors fail. Easy check, remove it and see if it rotates smoothly or if it jumps in to position.

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[PMT2000]

The servo motor seems to be fine. I was able to run it off of the X axis amp by turning off no-fuse breaker for the Z axis amp to clear the alarm. As it turns out, the servo wasn't even hooked up. I spotted the wires tucked in and not connected. So, there is something drawing excessive current with the servo disconnected. I guess I'll start checking the components mounted behind the servo amp. There are some relays, capacitors, and a small white box that the U V W motor wires also connect to and I have no idea what it is. Turning off the breaker only kills the DC power to the transistor bridge, the amp still gets a green light. This would seem to be further proof that the problem is isolated to the U V W circuit so it should be easy to find. But it's not! It has me pulling my hair out!

[PMT2000]

I finally figured it out. One of the transistor modules had a short in it. These are basically just black boxes that mount on the cabinet behind the servo amp board. Each one has four transistors in it. It took a lot of checking between all of the terminals to find the short. There are three of these modules and they are no picnic to get out either. We were able to get one off of E bay and the machine is now back up and running.

[cmoreno911]

Hi, I have the same problem on Okuma LB12 but I read your last post but where is this cabinet yo have any picture of this transistor

black boxes that mount on the cabinet behind the servo amp board

thanks
carlos