Yasnac Okuma Parameter Backup

title: Yasnac and Okuma Parameter Backup and Recovery category: machines tags: [yasnac, okuma, osp, mx3, mx2, mx1, j300, parameter, backup, battery, sram, recovery, spec-sheet] compiled: 2026-04-11

Summary

Yasnac and Okuma controls have their own parameter backup procedures distinct from [[fanuc-parameter-backup|Fanuc]]. This article covers Yasnac MX1/MX2/MX3/J300 controls (found on older Okuma lathes, Mazak machines, Takisawa, and Mitsui Seiki), and Okuma OSP controls (OSP5020, OSP7000, OSP-E100, OSP-P200, OSP-P300, OSP-U200). Same principles apply — battery-backed SRAM, periodic backups required, recovery is painful without them. Lose your parameters on a 1980s Yasnac and you're looking at a week of downtime and a five-figure service bill. A 30-minute backup prevents all of it.

Yasnac (Seiki) Controls — MX1/MX2/MX3/J300

These controls were manufactured by Yaskawa Electric (branded "Yasnac" or "Yasnac Seiki") and found on older Yamazaki (Mazak), Okuma, Takisawa, and Mitsui Seiki machines from roughly 1982 through the mid-1990s. The MX1 and MX2 are the earliest generations; the MX3 was the most widely deployed; the J300 (also called i80/i80M) was the final Yasnac generation before Yaskawa exited the CNC control market.

Key characteristics:

  • SRAM backed by a 3V lithium battery — typical life 3–5 years, sometimes less in hot electrical cabinets. Common battery types: CR series lithium coin cells or a battery cassette specific to the control PCB. Check the maintenance manual for your exact board revision — battery form factor varies.
  • Parameters stored in NC-param and PMC-data regions — NC parameters govern axis configuration, servo tuning, reference positions, pitch compensation tables, and coordinate system offsets. PMC (Programmable Machine Controller) data governs the machine-side ladder logic variables, timers, counters, and keep relays. Both are critical. Backing up only NC parameters and ignoring PMC data leaves you half-recovered.
  • External I/O via RS-232 DNC port only — no USB on classic MX controls. The MX3 typically has one or two RS-232C ports on the rear of the control unit. Some J300 controls added options for floppy disk or memory card I/O, but RS-232 remains the universal method.

Backup Procedure (Yasnac MX3 Specific)

  1. Set up the PC side first. Connect a PC with terminal/communication software (TeraTerm, PuTTY in serial mode, or a dedicated DNC package like Predator or CimCo) via a null-modem RS-232 cable to the control's RS-232C port. Match the baud rate to what the machine is set to — typically 4800 or 9600 baud, 7 or 8 data bits, even or no parity, 2 stop bits. These serial settings are stored in machine parameters (consult the operator manual for the specific parameter numbers on your revision — they vary between MX2 and MX3).
  2. On the control, navigate to the PARAMETER screen using the function keys.
  3. Enable I/O output mode. On most MX3 versions, you enter EDIT mode (key switch to EDIT position), then access the data I/O function. The exact key sequence varies — on some revisions it's the AUX or I/O soft key from the parameter display. The screen should show options like PUNCH OUT, READ IN, or similar.
  4. Select the data type to output: NC Parameters, Offsets, PMC Data, Macro Variables, Pitch Compensation, etc. Back up each one separately.
  5. Initiate the PUNCH OUT (or OUT) command. The control sends the parameter data as an ASCII text stream over RS-232. Your PC terminal software captures this stream — make sure you have "capture to file" or "log to file" enabled before you start the transfer.
  6. Save each file with a clear naming convention. Example: YMX3_LATHE04_NCPARAM_2026-04-11.txt, YMX3_LATHE04_PMCDATA_2026-04-11.txt. Store copies on a network drive and a USB stick kept with the machine documentation binder.
  7. Repeat for every data region: Offsets (tool length, work coordinate), custom macro variables, pitch compensation tables, user parameters. If in doubt, dump everything the I/O screen offers.

Restore Procedure

Reverse of backup: set the control to READ IN (or LOAD) mode, configure the PC to send the file, and transmit. Use software flow control (XON/XOFF) or hardware handshaking (RTS/CTS) as required — the MX3 typically uses XON/XOFF. Send at the same baud rate. The control will parse the incoming text and write it to SRAM. After loading, power-cycle the control and verify parameters on-screen before running any program.

Battery Replacement

Critical rule: Replace the battery WITH POWER ON. The SRAM is volatile — if you power down with a dead or removed battery, all parameters are wiped instantly. The battery is accessible on the CPU board or memory board inside the control cabinet. Typical procedure:

  1. Machine powered on, E-stop engaged.
  2. Open the control cabinet (follow lockout/tagout for the cabinet door interlock if applicable, but do NOT disconnect main power).
  3. Locate the battery on the PCB — it's usually a socketed lithium cell or a battery pack with a connector.
  4. Swap the battery. Some boards have a momentary power interruption tolerance of a few seconds; don't dawdle.
  5. Verify no battery alarm on the screen after replacement.

Yasnac controls typically display a battery alarm when voltage drops below approximately 2.5V (exact threshold varies by board revision — verify against your maintenance manual). Do not ignore this alarm. You have days to weeks, not months, once it appears.

If Parameters Are Already Lost

You need the machine's original spec sheet (also called the "parameter sheet," "machine constants sheet," or "initial parameter list") from the machine OEM. This document contains every NC parameter value, PMC data setting, pitch compensation table, and reference position as configured at the factory for your specific machine serial number.

  • Okuma-built machines with Yasnac controls: Contact Okuma America Corporation — (513) 636-0100, Charlotte NC service center. Provide the machine model and serial number (on the nameplate, typically on the main electrical cabinet or behind the operator station). They can email the original spec sheet for registered machines within a few business days.
  • Mazak machines with Yasnac controls: Contact Mazak service — (859) 342-1700, Florence KY. Mazak maintains archives for historical machines and can supply spec sheets.
  • Other OEMs (Takisawa, Mitsui Seiki, etc.): Contact the OEM directly. If the OEM no longer has US representation, aftermarket CNC service companies that specialize in Yasnac (search for Yasnac repair services) sometimes have parameter archives.

Without the spec sheet, recovery requires trial-and-error parameter entry plus ballscrew pitch compensation re-mapping with a laser interferometer — typical cost: $3,000–$8,000+ for the service call, 3–10 days downtime. This is the single most expensive consequence of not maintaining backups.

Okuma OSP Controls (OSP5020 through OSP-P300)

Okuma's own OSP control family is entirely distinct from Yasnac. Okuma licensed Yasnac controls from Yaskawa for some older models, then transitioned fully to their own OSP platform. The OSP architecture, parameter format, and backup methods are Okuma-proprietary.

OSP5020 / OSP7000 (1990s)

  • RS-232 parameter dump, similar workflow to Yasnac but with Okuma-specific file formatting.
  • Use Okuma's "OKUMA COMMUNICATOR" PC utility if available — it handles the protocol correctly. Alternatively, TeraTerm capture works but you must verify the file header/footer formatting is intact for restore.
  • Parameters, tool data, common variables, and machine constants are separate data sets — dump all of them.
  • Battery-backed SRAM, same rules: replace battery with power on.

OSP-E100 / OSP-U10M / OSP-U100 (Late 1990s–Early 2000s)

  • RS-232 standard; some later revisions added Ethernet (10Base-T).
  • Parameter backup accessible via specific screen combinations — typically navigate to the maintenance or diagnostic area, then select data I/O functions.
  • Okuma's "OSP Parameter Save" utility is the preferred tool if your service package includes it. It handles all data regions and formats the files for clean restore.
  • The OSP-U100 introduced optional CF card or PCMCIA card backup on some configurations — check your machine's option list.

OSP-P200 / OSP-P300 / OSP-P500 (2005+)

  • USB port on most machines — this is the primary backup medium for most shops.
  • Ethernet/network available on most configurations.
  • The OSP-P series runs on a Windows-based HMI internally. On newer revisions, the parameter files are accessible via the Windows file system using Okuma's maintenance mode (sometimes called "service mode" or accessed via a specific key combination at boot).
  • Standard backup procedure: Navigate to Maintenance → Parameter (or Data I/O, depending on software version) → Save to USB or network share. The control writes out files in Okuma's proprietary format. Keep the entire folder structure intact — don't rename or reorganize the output files.
  • THINC API on OSP-P200 and later allows automated backup scripts if your shop has the THINC development package.
  • Much friendlier than older OSP or Yasnac, but the same fundamental risk applies: if the backup doesn't exist, recovery is expensive.

Recovery Without a Backup

If the battery died and parameters are gone:

  1. Get the machine serial number from the nameplate — usually on the main electrical cabinet door, the headstock casting, or behind the operator station. Write it down and photograph it.
  2. Contact Okuma America Corporation — (513) 636-0100, Charlotte NC parts/service. Provide the serial number and machine model. They maintain parameter archives and can email the original spec sheet. Turnaround is typically a few business days, sometimes faster for active service contract customers.
  3. For Yasnac on non-Okuma machines, contact the machine OEM — Mazak service at (859) 342-1700, Florence KY has spec sheets for their historical Yasnac-equipped machines. For other builders, contact the OEM's service department directly.
  4. Re-enter parameters one at a time from the spec sheet using the NC-Param screen. Verify each value before moving to the next. PMC data entry is tedious — hundreds or thousands of values on a complex machine.
  5. Re-establish reference (home) positions for all axes. This typically requires jogging each axis to a known mechanical limit or reference mark (dog, decel cam, or grid shift point) and setting the home position parameter. On machines with absolute position encoders, re-zeroing may require the encoder setup procedure from the maintenance manual.
  6. Re-enter pitch compensation tables if they were not included in the spec sheet or backup. Without a laser interferometer measurement, you can enter the factory values from the spec sheet, but accuracy may have drifted since the machine was new.
  7. Run a test program at single-block with rapid override at 25% and feedrate override reduced. Use a dial indicator or touch-off to verify axis positions match expected values before trusting the machine for production work.

Backup Schedule

  • Immediately after any service work or battery replacement
  • After any parameter change — axis tuning, spindle orientation setup, pitch compensation update, PMC logic modification
  • Monthly as a standing procedure — put it on the PM calendar
  • Before and after control software updates or retrofits
  • Before extended shutdowns — holidays, plant moves, or any period where a battery failure could go unnoticed

Store backups in at least two locations: a USB stick kept physically with the machine, and a network drive or cloud folder. Label files with machine ID, date, and data type. Old backups are better than no backups — don't delete previous versions.

  • [[fanuc-parameter-backup]] — similar principles for Fanuc controls
  • [[haas-common-alarm-codes]] — related troubleshooting for Haas machines
  • [[rs232-serial-communication]] — RS-232 cable pinouts and serial setup for CNC data transfer
  • [[cnc-battery-replacement]] — general battery replacement procedures across control brands