View Full Version : Okuma LB15 201 Drive Alarm

02-02-2015, 09:31 AM
Hello All,
We have this problem with an Okuma LB15 (OSP5000) lathe, any advice would be much appreciated.
On start-up the machine often boots to the main screen but with Alarm 201.
The Okuma manual describes this as a possible BDU fault or a Servo PSU fault.
Also, immediately at mains power-on, the Z-axis drive shows red LV LED. (is this normal?)
For this' the manual says replace either BDU or Servo PSU.

Eventually, it does becomes possible to reset the machine, but this can take hours.
Here's the detail on how we have progressed so far...
Machine giving Alarm “201-4 Alarm A Servo Amp Z Axis” Error
(Sometimes we get 201-3 X axis error instead?)
Tried to restart numerous times, same error.
Proceeded to check all voltages:
Incoming 415v 3ph = 416v
200v 3ph from transformer = 200v
Transformer tapping was set to 415 = OK
100vac = 102vac
110vac = 112vac
LV Power Supply...
5vdc = 5vdc
12vdc = 12vdc
24vdc = 24vdc
ISO 24vdc = 24vdc
All these values appear to be OK
Red LED on BDU Servo PCB indicating “LV Error”
Red LED on Servo P/supply indicating “LV Error” (This not always on)
LV refers to DC Drive power was below 200vdc.
Located DC Bus supply (HV and LV) tested and was at 288vdc
(Checked adjacent machine (which was running) this also at 288vdc) (but this other machine also gives same 201 error but much less frequently).
Also occasional Red LED “IOCS” on Servo Amp PCB (BDU)
This refers to “More than 120% transistor rated current flowed through transistor bridge” (Power transistors feeding motor)
Disconnected Z axis motor terminals, powered up and fault had cleared.
Did this restart twice and was ok both times. Reconnected motor, powered up, fault re-occurred.
Disconnected motor again, but this time the 202 fault reappeared.???
Noticed that red LED “LV” on servo PCB comes on as soon as isolator is turned on, not sure if this is normal?
This also happened when motor was not connected but extinguished when CNC had fully booted up.
The Okuma maintenance manual has action for these faults...
If BDU LV LED then “Replace BDU Unit, Replace Servo DC P/Supply”
If IOCS LED then “Replace BDU Unit”
If the Okuma manual is correct, I believe I am unable to progress much further without parts.
Even so, could the machine may be incorrectly reporting that these parts require exchanging?
Without spares to swap out we cannot be absolutely sure.
The IOCS fault was strange, indicating high current in the motor drive transistors? (This happened when motor was still connected) I wonder if there is an issue with the servo drive power section (behind PCB)
The motor was checked (multimeter only) and showed balanced phases at approx.1 ohm, and over 20 Megohm to earth. (Did not have ‘Megger’ to test earth)
Is it possible that the drive DC bus (LV-HV) at 288Vdc is too low?
Any help/advice much appreciated.