Resolving Siemens Sinumerik 840C PLC 43 ORD1 Error and HDD Black

Problem Overview

The Siemens Sinumerik 840C control, particularly as deployed on Hyundai HIT-series machine tools (HIT-15S through HIT-30S, often branded HiTrol 840C), exhibits a documented multi-fault failure mode after CMOS battery service. Operators typically see two messages stacked on the operator panel: a missing-workpiece file warning of the form There is no workpiece <Name of File>, followed by 43 ORD1 PLC-CPU not ready for operation. If a hard-disk image is then restored to recover the missing files and the source image is not bit-identical to a known-good backup, the system can drop to a non-bootable state displaying Remove disk/media. Press any key to restart on a black screen, with no response from the integrated keyboard or any attached external keyboard.

The 840C predates the SINUMERIK PCU/NCU split and consolidates the HMI, NC kernel, and integrated PLC on a single industrial-PC platform whose boot media is a PATA/IDE hard disk. Because the HDD stores the NC runtime, the PLC user program, machine data, tool offsets, and workpiece directories, a partially written or truncated image can render the control unbootable even when the disk hardware itself is healthy. The repair path is therefore: (1) recover a known-good image to a different HDD, (2) bring the PLC back to a clean state with the documented general-reset / clear / forceboot sequence, and (3) re-establish the NC-to-PLC link before powering the drives.

Affected Hardware and Control Architecture

The 840C is a SINUMERIK family controller introduced in the late 1980s and produced well into the 1990s, designed around an MMC (Man-Machine Communication) industrial PC coupled to an NC section and an integrated SIMATIC S5-class PLC. On Hyundai HIT turning centers the controller is delivered as a single enclosure commonly referred to as the MMC CPU, containing the 840C mainboard, the integrated PLC module, the hard disk, and the floppy drive.

The integrated PLC shares the same power and bus structure as the NC kernel; if the NC kernel fails to load cleanly, the PLC remains in its stop state and reports not-ready to the NC. This is the underlying mechanism that produces error 43 ORD1 on the operator display even when the PLC module hardware is intact.

Error Code Reference

Error 43 in the 840C alarm schema is the PLC not ready class. The ORD1 suffix is the alarm index the HMI appends to disambiguate concurrent PLC stop conditions; on a freshly battery-served system, the dominant cause is the PLC not having been cold-started against the post-restore machine data set.

Root Cause Analysis

Three contributing factors appear in the field history of this fault and should be ruled out in order before any destructive action is taken on the HDD.

1. PLC retained in stop after CMOS service. When the lithium cell is removed with power applied (the procedure recommended in the 840C service manual to preserve BIOS settings), the PLC user program and the NC machine data are unaffected, but the PLC enters a non-initialized state on the next cold start. The NC subsequently times out waiting for the PLC ready bit and raises 43 ORD1. The normal recovery is the general-reset / clear / forceboot sequence described below.
2. Workpiece directory not yet populated on the new boot. A program selection made before the directory is rebuilt, or a part-program name that lives in the operator's notes but not on this HDD, produces the There is no workpiece prompt. This is an HMI message, not an alarm, and is benign once the correct file is transferred.
3. Restored image is not a true sector image. A file-level copy of a 840C HDD (for example a drag-and-drop of the DOS tree from a Windows host) will not preserve the boot sector, the partition table, or the hidden NC-system files. When written back, the system may POST the disk successfully but fail to find an operating system and drop to the Remove disk/media prompt. A bit-level (dd, ghost, or similar) image of the original HDD is required, and the destination disk must match the geometry (cylinders, heads, sectors) expected by the 840C BIOS or be reparameterized identically in the BIOS setup.

Pre-Restoration Diagnostic Procedure

Before writing any image to a disk, perform the following checks in this order. Each step takes only a few minutes and protects the last known-good backup from being overwritten.

1. Confirm the backup media itself. Mount the backup HDD as a secondary drive on a service PC with a 40-pin IDE adapter (or in a USB-IDE dock that exposes the disk as a mass-storage device, not a CD-ROM). Use a sector editor to verify the first 512 bytes contain a valid partition table (signature 0x55AA at offset 0x1FE) and that the first sector of the active partition contains a recognizable DOS boot record.
2. Verify the destination HDD. Run a short S.M.A.R.T. or surface scan. The 840C BIOS is sensitive to bad sectors in the first few hundred megabytes; even a single unreadable sector in the NC kernel region will produce intermittent PLC not-ready alarms.
3. Check the CMOS battery orientation and voltage. A reversed cell can leave BIOS settings valid for a short window but cause corruption on the next power cycle. Measure the battery holder voltage under load before proceeding.
4. Document the BIOS settings. Photograph or write down HDD geometry, boot order, and any enabled shadow RAM options from the 840C BIOS setup screen. A default-loaded BIOS will often re-detect the HDD with a different translation than the original, which alone is enough to render a previously valid image unbootable.
5. Test the integrated keyboard connector. With the control powered down, reseat the keyboard ribbon at the MMC CPU end. A misaligned pin on the FPC connector is a common source of "no keys respond" on Hyundai HIT enclosures.

PLC General Reset, Clear, and Forceboot Procedure

The PLC recovery sequence documented for the 840C integrated PLC has three discrete steps. Each must complete successfully before the next is attempted; do not skip the clear, as a general reset without a subsequent clear leaves stale output image tables in PLC RAM.

1. Enter general-reset mode. From the operator panel, navigate to the PLC service area (the exact menu path varies with the installed HMI version, but is typically Diagnosis > PLC > Service or accessible via a hidden key combination on the integrated keyboard). Place the PLC in general-reset (cold-restart) mode. The PLC status LED on the MMC CPU will change from a steady RUN indication to a slow blink.
2. Execute PLC clear. Trigger the PLC clear function. This wipes the PLC user program from PLC RAM, leaving the PLC in the same state as a freshly delivered module. Confirm the HMI reports the clear completed; on the 840C this is usually a short PLC CLEAR OK line in the service log.
3. Forceboot the PLC. Initiate a PLC forceboot (cold restart with reload from the HDD-resident user program). The PLC will read its program file from the HDD's PLC directory, initialize the I/O image tables, and transition to RUN. The status LED returns to steady RUN, and the 43 ORD1 alarm should clear within one NC cycle (typically < 1 s on the 840C).

HDD Image Restoration Best Practices

The single most damaging step in this failure mode is a restoration that overwrites the only working HDD with a faulty image. Treat the live HDD as evidence until a spare is known-good.

1. Obtain a verified spare HDD. Match the capacity to the original (the 840C BIOS typically uses CHS translation; a much larger disk may be mis-translated and produce a too-small partition). Standard 5400 RPM 3.5" IDE drives in the 1-4 GB range are appropriate for the original image.
2. Write the image to the spare first. Use a Linux host with dd for a sector-level copy, or a commercial imaging tool set to raw mode. A file-level copy is not acceptable. Example minimal command sequence: dd if=hit840c_backup.img of=/dev/sdb bs=512 conv=noerror,sync status=progress. The noerror,sync flags preserve the byte stream on unreadable source sectors so the destination remains bootable even if the source had minor media degradation.
3. Boot the control from the spare. Disconnect the original HDD before connecting the spare to avoid the 840C BIOS being confused by a master/slave conflict. Confirm the spare boots cleanly to the HMI before any further action.
4. Bring up the PLC. With the spare booted, perform the general-reset / clear / forceboot sequence from the previous section. Verify the 43 ORD1 alarm clears.
5. Validate the workpiece directory. From the HMI, list the workpiece directory. If a previously known file is still missing, transfer it via the floppy drive (the 840C ships with a 1.44 MB drive in the MMC) or via RS-232 to the spare, then re-test the program selection that originally produced the There is no workpiece message.
6. Only after the spare is fully validated, bring the production HDD back online if required, or re-image the original HDD from the now-verified spare.

Recovering from "Remove Disk/Media" Black Screen

The Remove disk/media. Press any key to restart prompt is a BIOS-level message, not an HMI alarm. It means the POST completed but no bootable device was found on the primary IDE channel. In the context of this fault, the cause is almost always that the restored image lacks a valid boot sector or that the BIOS has reverted to default HDD parameters.

1. Power down, wait 30 s, power up. A genuine BIOS re-enumeration is required; the 840C BIOS will not hot-redetect an IDE device.
2. Enter BIOS setup on the first prompt. The 840C BIOS setup is typically entered with DEL or F2 during the early POST. If the integrated keyboard is unresponsive, confirm the FPC connector before assuming keyboard failure.
3. Restore HDD parameters. Set HDD type to User and enter the original geometry (cylinders, heads, sectors) recorded in the pre-restoration diagnostic. If the original geometry is unknown, set the type to Auto and let the BIOS detect, then verify the reported translation matches the original; a mismatched translation is a common cause of unbootable images that were written correctly at the sector level.
4. Confirm boot order. The 840C should boot from the primary IDE master. Floppy first is acceptable for service work but will re-trigger the prompt once the system tries to leave the floppy drive.
5. Save and exit. The system will reboot. If the image is valid and the geometry matches, the HMI will begin loading within 10-30 s.

Verification Procedure

After the recovery, run a structured verification before returning the machine to production.

Preventive Maintenance Schedule

Escalation Path: MMC CPU and HDD Replacement

If the integrated PLC module within the MMC CPU is itself damaged, or if no bootable HDD image can be produced from any available source, the practical escalation is to obtain a replacement MMC CPU and a known-good HDD from the machine builder. On Hyundai HIT-series machines, the OEM (Hyundai WIA and successor organizations) historically provided spares and image media directly. Before contacting the OEM, capture:

• The machine serial number and the 840C software version string from the HMI's Diagnosis > Version page (still readable on a working control; recover from the spare before sending the original out for repair).
• The PLC user program and NC machine data exports.
• The full part-program directory, including the tool list and the active work offsets.
• The axis configuration (which axes are present, their scaling, and their drive type).

This data set allows the OEM to ship a replacement MMC CPU pre-configured for the specific machine, dramatically reducing the commissioning time on the customer site. The Siemens Industry Online Support portal maintains a SINUMERIK archive section with operating, programming, and installation manuals for the 840C family; consult it for the version-correct documentation before quoting any machine-data values to the OEM.

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