SINUMERIK 810T Alarm 6000 Recovery: Post-Transport JOG Restore

Problem Identification: NC Alarm 6000 on a SINUMERIK 810T After Intercontinental Transport

The reported fault — NC alarm 6000 displayed on a SINUMERIK 810T (part number 6FC3171-OAA-Z, F-Nr A 1477632) installed on a Monoforts-MNC 602E turning centre (M. Nr. W20305, build year 1987) — is a classic PLC STOP condition that disables every motion mode, including JOG, MDI and AUTO. The user PLC alarms 6000, 6004 and 6005 are latched simultaneously with PLC machine-data alarms 7000, 7006 and 7009. After the machine was moved from Germany to the UAE, the operator panel reports the NC kernel as alive, but no axis can be jogged because the integrated STEP 5 PLC is held in STOP by its own alarm handler.

On the SINUMERIK 810T platform, NC alarm 6000 is the dedicated "PLC STOP" indicator. The NC kernel of the 810T performs all path interpolation and handshakes with the integrated PLC through a dual-port RAM interface. When the PLC is not running its cyclic OB1, the NC receives no PLC ready flag and immediately raises alarm 6000. The 6000–6063 user PLC alarms and the 7000–7063 user PLC-MD alarms are therefore frozen in their last latched state — they represent the trigger condition, not a current measurement.

Resolving the JOG fault therefore requires a disciplined sequence: confirm incoming power, recover the PLC from STOP, translate the German FB1/FB2 alarm logic to identify which of the user alarms 6000/6004/6005 actually holds the PLC down, restore the R-parameter and machine-data files (RPA0–RPA3) from backup, and only then verify each axis enable path from the operator panel down to the Simoreg power section. The reference document for the platform is the SINUMERIK 810T Operating Manual, Software Version 3 (GA3, file 368_810T_GA3_Operating.pdf).

System Identification: SINUMERIK 810T Variant 6FC3171-OAA-Z

The Siemens ordering code 6FC3171-OAA-Z decodes as follows. The 6FC3 prefix identifies a SINUMERIK CNC; the 171 sub-range designates the 810T turning control hardware generation; the OAA block is the basic software release of the 810T; the trailing -Z is a customer-specific (Sonderausführung) variant made exclusively for a specific OEM. In this case the OEM is Monoforts-MNC, whose 602E turning centre from 1987 carried this special build. The implication is critical: standard Siemens documentation only describes the generic 810T behaviour, while the I/O map, PLC interface bits and alarm texts are defined in the customer %PCA file and the FB1/FB2 blocks supplied on paper in German.

The 810T control unit itself houses three modules: the NC module (CPU, position control, MMC interface), the PLC module (Intel 80286 era with STEP 5 firmware) and the I/O backplane with the MMC floppy drive. The 24 V DC supply feeds only the control electronics; the axis drives (Simoreg 6RA22 or similar DC choppers from that period, fed from a three-phase 400 V supply) and the spindle drive are powered separately. A failure in the 24 V rail therefore impacts every operator action but does not, by itself, indicate a drive-side fault.

Reference: SINUMERIK 810T Operating Manual, GA3.

Alarm Code Reference and Translation

Alarms on the 810T are split between the NC kernel and the integrated PLC. The NC kernel raises the 6000 alarm when the PLC fails to deliver its readiness handshake. The PLC raises 6000-series and 7000-series alarms according to the customer's FB1 alarm-mask block; these are not Siemens-defined messages but Monoforts-specific text stored in DB1 and indexed by the alarm handler.

Procedure: power up the control, allow NC 6000 to display, and read the four-line alarm line on the operator panel (CRT or 8" display). Record the EXACT alarm numbers and any sub-codes before attempting a PLC reset — once OB1 starts running, some latched alarms will clear on their own and the root-cause evidence is lost.

Transport-Induced Failure Modes (Climate, Vibration, Battery)

A move from Germany to the UAE exposes the 810T to three damaging vectors: thermal cycling during container transport, sustained high ambient temperature on arrival, and possible sand/humidity ingress through any unsealed cabinet. Each of these maps to specific component failures inside the 37-year-old electronics.

Pre-Power-Up Inspection Procedure

1. Verify cabinet environment: ambient below 35 °C, no condensation on cold surfaces, all cabinet doors closed and seals intact.
2. Measure the 24 V DC supply at the 810T backplane input terminals with the supply energised but the control OFF. Acceptable window: 24.0 V ±10 % (21.6–26.4 V). Ripple < 100 mV pk-pk.
3. Measure the 400 V three-phase supply at the drive section line input. Confirm phase rotation (clockwise field) using a phase-rotation tester; German machines are typically wired for clockwise rotation.
4. Measure the 810T backup battery voltage on the NC module under a 10 mA load. Replace any cell reading below 3.0 V before proceeding — the cost of a new lithium cell is trivial compared with reloading all machine data.
5. Visually inspect every plug-in module for gold-finger corrosion, capacitor venting, and burned PCB areas. Reseat each module at least once to clear oxide from the backplane contacts.
6. Inspect the MMC floppy drive head for dust; clean with isopropyl alcohol if needed. The 810T uses standard 3.5" DS-DD floppy disks formatted at 720 KB — verify availability of working media.
7. Confirm the E-stop button is mechanically released and the safety relay is closed (24 V present at its coil terminals).

Restoring PLC Operation: Clearing NC Alarm 6000

The integrated PLC of the 810T is a STEP 5 controller with OB1 (cyclic), OB2 (interrupt) and OB21/OB22 (restart) blocks. When OB1 is not executing, the NC displays alarm 6000. Recovery is sequential: identify why OB1 stopped, restart the PLC, then clear the latched user alarms.

1. From the Setup menu, select PLC → PLC STATUS and read the PLC operating-state field. Expected readings: RUN (cyclic), STOP (held), RESTART (warm restart pending).
2. If state is STOP, scroll to the PLC ISTACK (interrupt stack) and record the OB number that caused the stop. Common causes: OB13 (time-tick error), OB21 (restart fault), programming error in FB1.
3. Press the PLC STOP RESET soft-key. The PLC will attempt a warm restart. If it falls back to STOP immediately, the ISTACK indicates a permanent fault — most often a battery-emptied DB block with invalid BCD data.
4. If warm restart fails, force a cold restart: hold the RESET and CANCEL keys simultaneously while powering up the control. This reloads defaults but wipes unsaved parameters.
5. Once the PLC reaches RUN, NC alarm 6000 clears within one PLC cycle (≤ 40 ms). The PLC user alarms 6000/6004/6005 will clear only when their underlying conditions are resolved.

Decoding the Backup File Set (TEA, RPA, PCA, FB, DB)

The backup provided with this machine comprises both controller files and printed PLC listings. Each file type has a fixed role inside the 810T and must be restored in a specific order to obtain a coherent control state.

Load sequence on site:

1. Power up the 810T; wait for the NC to finish its self-test (about 25 seconds from cold start).
2. Connect a Siemens PG635 / PG675 / PG720 programming device to the PLC serial port (RS-232, 9600 baud, even parity). Load %PCA, then FB1, FB2, DB1–DB7 in that order. Verify each block accepts with ACK.
3. Insert the formatted 3.5" floppy containing TEA/RPA files into the MMC drive. From the Setup menu select Read in → All. The 810T will load RPA files first (modal arithmetic), then the zero-offset file, then the TEA part programs.
4. After the load completes, cycle control power once to commit parameters to battery-backed SRAM.

Translate the German alarm text in DB1 using the table below before relying on any single alarm index for troubleshooting — Monoforts used non-standard wording relative to Siemens generic texts.

Power Supply Verification (24 V DC, 120 W)

The 810T draws 5 A nominal from the 24 V DC rail (120 W / 24 V = 5 A). The 24 V supply must be a regulated, low-impedance source — typically an SITOP power supply or a Siemens 6EP1 unit on machines of this era. The 400 V drive bus is separate.

Voltage-drop check on the 24 V wiring: with 5 A flowing on the supply lead, measure the drop end-to-end. A drop > 0.5 V indicates undersized cabling or a corroded terminal — both common on a 37-year-old cabinet. Use the formula V_drop = 2 × I × L × ρ / A (round trip) where ρ for copper = 0.0172 Ω·mm²/m, L is single-way length in metres and A is conductor cross-section in mm². For a 10 m run at 5 A on 2.5 mm² copper: V_drop = 2 × 5 × 10 × 0.0172 / 2.5 = 0.69 V — already marginal. Reduce to 4 mm² copper or shorten the run.

Battery backup sizing: the 810T SRAM draws approximately 50 µA continuously. With a 1.2 Ah primary lithium cell the theoretical retention time is 1.2 Ah / 50 µA = 24 000 h = 2.7 years. Add a 50 % derating for self-discharge at 40 °C UAE ambient and the practical replacement interval is about 18 months. Replace prophylactically every 2 years on machines in hot climates.

Axis Drive and Operator Panel Verification

The Monoforts 602E of 1987 typically used Simoreg 6RA22 or 6RA27 DC choppers for X and Z axes (60 A to 120 A armature, depending on axis) and a Simoreg 6RA22 spindle drive with a four-quadrant reversible armature. Each drive receives its enable from the PLC via dedicated output bits in the NC interface.

1. Verify the Simoreg drive unit shows no alarm (green "READY" LED). On a 6RA22, the 7-segment display reads -- when healthy; any number indicates a specific fault (consult the 6RA22 diagnostics manual).
2. With the PLC running, force the X-axis enable bit (typically Q 0.0 in the %PCA assignment) from the PG. The Simoreg should pick up and the X motor should hold torque against manual rotation.
3. Repeat for Z and spindle. Any axis that does not pick up reveals either a wiring break, a missing 24 V signal from the PLC, or a Simoreg field-supply fault.
4. Test the operator panel membrane. The Monoforts 602E used a custom membrane that ages badly in heat. Stuck keys or open-circuit keys will keep the corresponding PLC input permanently 1 or 0 — for example, a stuck EMERGENCY STOP key will hold the PLC in STOP and prevent JOG.
5. Check the actual EMERGENCY STOP chain: E-stop button → safety relay → drive enable contactor → drive pulse inhibit. Each element must be closed (de-energised = safe). A single open contactor will deny all drive enables and JOG will fail silently.
6. Check the Simoreg field supply. A 6RA22 with a missing field reads alarm code 04. On machines stored for long periods, the field-current potentiometer drifts; recalibrate per the 6RA22 commissioning checklist.

Machine Data Reset and PLC MD Alarm Resolution

PLC MD alarms 7000/7006/7009 are "machine-data alarms" — they fire when a specific numeric MD in the integrated PLC is out of range. Typical Monoforts assignments:

Procedure to edit a user MD on the 810T:

1. From the operator panel, enter SETUP → PLC MD.
2. Use the cursor keys to navigate to the index (e.g. MD 9006) and press INPUT.
3. Type the new value (e.g. 0) and confirm with OK.
4. Press the CANCEL ALARM soft-key to clear the latched alarm.

Some user MDs are read-only and require a PG connection to the PLC for editing via STEP 5. The exact access path depends on the Monoforts-specific FB1 implementation. Reference the FB1 listing supplied with the machine (German printout) and the corresponding data block (typically DB3 or DB4) to confirm the MD layout.

JOG Mode Verification Sequence

Only after every section above has been completed may the machine be considered ready for a JOG test. Execute the following sequence in order, verifying each step before proceeding.

1. Control in OPERATION mode, NC alarm line clear (no NC 6000, no latched PLC alarms).
2. Mode selector on JOG.
3. Feed-rate override at 0 %, then increase to 10 % for the first motion.
4. Press the + X-axis key. The X motor should rotate at the slow jog speed (default 2 000 mm/min on the 810T, settable via MD).
5. Verify the Simoreg 6RA22 armature current on the X drive matches the expected no-load value (typically < 5 A for a 60 A drive).
6. Press the + Z-axis key; verify Z motion and current.
7. Press RAPID; verify fast jog speed (typically 8 000 mm/min).
8. Test the feed-hold button and the emergency stop. The drive should drop to zero torque within 50 ms.
9. Re-reference both axes in REF mode and verify the reference-point offset is stable (repeatable within ±0.005 mm).

If any step fails, do not continue. Return to the relevant section above and re-diagnose.

Long-Term Considerations for the 810T Platform

The SINUMERIK 810T has been out of Siemens production for over two decades. Spare modules (NC CPU, PLC CPU, I/O cards) are no longer manufactured and are sourced exclusively from European dismantling yards. The refurbishment cycle on these boards is typically 6–12 months because of electrolytic capacitor ageing. Owners of 810T-controlled machines should plan either an electronics refurbishment every 5–7 years or a migration to a current Siemens platform such as SINUMERIK 828D or 840D sl. The Siemens migration service preserves the existing part programs and tool data via standard STEP 5 → STEP 7 conversion, but requires new drives and a new operator panel. For Monoforts 602E mechanics, a retrofit with SINUMERIK 828D plus SINAMICS S120 drives is the most common path; the existing DC motors can be retained with S120 6SL3xxx DC link adapters in legacy installations.

Frequently Asked Questions