Troubleshooting SINUMERIK 810T GA3 Alarm 1120 X Axis Clamping

Problem Overview

A Siemens SINUMERIK 810T GA3 controlled lathe presents a recurring alarm 1120 ORD 2 X Clamping Monitoring during production, eventually forcing random mid-cycle stops. After replacement of the X-axis drive module, additional alarms appear:

• 2000 Emergency Stop (E-Stop)
• 6034 Turret Not Ok (machine builder alarm)
• Automatic Stop. Auto Interrupted CH-1 channel message

Simultaneously, the hydraulic unit fails to start, the operator panel intermittently fails to boot, and the operator cannot reference the X-axis. This article decodes the alarm chain, isolates the root cause candidates (drive, encoder, hydraulic interlock, E-stop circuit, turret PLC interface), and provides a field-proven diagnostic and repair procedure for 810T GA3 retrofit and OEM lathes.

SINUMERIK 810T GA3 System Architecture

The SINUMERIK 810T GA3 (Software GA3) is a turning-variant CNC for 2-axis lathes (X, Z) plus spindle. It shares the same NCK/PLC kernel as the 810M GA3 (milling) but uses turning-specific cycle packages (CYC95 stock removal, CYC97 thread, etc.) and lacks the milling-specific cycles. The "GA3" suffix indicates a specific firmware generation; later retrofits used GB, GA1, GA2, and on the 810D platform the SW transition moved to HMI Embedded.

On many 810T lathes the X and Z axes are powered from a single 6SC6100/6SC6500 dual-axis module (commonly 6SC6500-0AB or 6SC6100-0BB). The operator panel is connected to the CCU via coaxial cable on early builds and twin-lead / ribbon on later builds. The PLC program is the same STEP 5 source across most 810T variants; only the user program and machine data change between machine builders.

For deeper architecture detail, refer to the SINUMERIK 810T GA3 Operating Manual and the SINUMERIK 810T GA3 Diagnostics Manual on Siemens Industry Online Support.

Decoding Alarm 1120 ORD 2 X Clamping Monitoring

Alarm 1120 belongs to the Siemens standard alarm set for SINUMERIK 810 / 820 / 840. The structure is:

• 1120 - alarm number assigned to "Clamping monitoring" in the 810 / 820 / 840 alarm catalog.
• ORD 2 - axis identifier from the machine data. ORD 2 is the second "logical axis" in the axis configuration. On a 2-axis lathe with spindle the default is X = ORD 2, Z = ORD 1. On a mill this would be Y; on the 810T lathe, ORD 2 is the X axis.

The semantic meaning is: the X-axis clamp release is being requested (or expected) by the NC, but the clamping monitoring signal has not transitioned to the expected state within the configured window.

On most 810T lathes the X-axis slides on a hydraulic-brake slide. The slide is held in position by a spring-applied / hydraulically-released brake (fail-safe design). When the operator selects an axis via the handwheel, MPG, or AUTO, the NC issues "controller enable" and "clamp release" to the PLC. The PLC energises a 24 VDC solenoid that routes hydraulic pressure to the brake-piston cavity, mechanically releasing the brake. A pressure switch or proximity switch then confirms the brake is open. The PLC feeds this confirmation back to the NCK via a dedicated I/O (commonly on a PLC135WB digital input module). The NCK expects the confirmation within a time window configured in the clamping-monitoring machine data (MD 28xx / MD 36xx range on 810 / 820, OEM-specific).

If the confirmation does not arrive, or arrives in the wrong state, the NCK raises 1120 and disables the axis. This is a safety function: it prevents the NC from commanding motion on a slide that the safety logic has not confirmed is movable.

Common root causes for 1120 ORD 2

1. Hydraulic pressure below the brake-release threshold (pump failure, low oil level, blocked filter, blown seal in the brake piston).
2. Brake-release solenoid coil open or shorted.
3. Pressure switch / proximity switch misadjusted, failed, or wired with a broken conductor.
4. PLC input module channel failure (commonly a stuck-high or stuck-low digital input).
5. Drive controller-enable signal missing (the drive does not pulse-enable, so the brake release is not requested at all).
6. NCK-PLC interface data corruption after a power dip, requiring NCK cold restart.

On the failing machine the original X-axis drive was found to be at fault. A failed drive can pull the controller-enable / pulse-enable line low, which keeps the brake released while the NC is still trying to verify a release confirmation - or it can keep the drive in an error state that prevents the NC from issuing the release request at all, causing the monitor to time out and raise 1120.

Cascading Fault Pattern: 2000, 6034, and Hydraulics Lockout

After the drive is replaced, the machine exhibits a different but related set of faults. The alarm chain is a cascade, not a list of independent problems. Treat them as one fault with multiple symptoms.

Alarm 2000 Emergency Stop

Alarm 2000 is the SINUMERIK standard "Emergency Stop" alarm. It is triggered whenever the NCK receives an E-stop signal from the PLC (or loses a controller-enable signal that the PLC interlock chain treats as E-stop). On the 810T the E-stop chain is wired into the PLC via a single input (commonly I33.0 on the 810T PLC convention) and the NCK hardware E-stop line on the CCU. When 2000 is active, the NCK:

• Disables all drives (pulse and controller enable dropped).
• Locks the spindle (no CW/CCW, no orientation).
• Rejects NC Start and M-functions for spindle motion.
• Prevents reference-point approach (G74 / G75) until E-stop clears.

Critically, 2000 also gates the hydraulic-unlock request at the PLC level on most lathes. The PLC refuses to energise the hydraulic pump contactor (commonly K0) until the E-stop is fully reset. Hence "the hydraulics won't come on" is a symptom of an unresolved 2000, not a separate fault.

Alarm 6034 Turret Not Ok

Alarm 6034 is not in the Siemens standard alarm catalog for 810 / 820 / 840. It is a machine builder (OEM)-defined alarm raised by the turret PLC program. On retrofit and OEM lathes, alarm numbers in the 6xxx range (and sometimes 5xxx) are reserved for user PLC %FC / %FB messages - the same convention that allows the OEM to define its own alarm text. The text "Turret Not Ok" tells you the PLC's turret-in-position-and-locked state machine has not reached the ready state. Causes include:

• Turret rotation motor contactor not pulled in (aux contactor or overload tripped).
• Turret clamping proximity switch not made (turret not seated).
• Tool-count parity error or tool-number mismatch between PLC and NCK tool table.
• The PLC is itself held in stop because of the upstream 2000 E-stop - meaning 6034 is a child of 2000, not an independent fault.

Operator panel not booting

An operator panel that "sometimes won't come on" after a drive fault usually points to one of three causes on the 810T GA3:

1. DC link sag on the 24 V logic supply. A shorted drive module can pull the 24 V rail down. After the new drive is installed, confirm that the 24 V supply is clean and within +/-10 % at the OP power terminals.
2. Corrupt NCK / PLC startup because the NCK was powered off mid-cycle. Perform a full NCK cold restart (described in the procedure below).
3. Loose coaxial / twin-lead connection between the CCU and the OP. With the new drive installed the cabinet may have been moved; check the ribbon cable seating on the back of the OP030.

Fault cascade diagram

The relationship between the alarms can be visualised as a fault tree. The SVG below summarises the dependency - the goal is to recognise that 1120, 6034, and the hydraulic lockout are all downstream of 2000.

Dual-Encoder X-Axis Configuration on 810T Lathes

The failing machine is described as having two encoders on the X axis: one on the servo motor, one on the opposite side of the motor. This is a standard Siemens dual-encoder setup for semi-closed / closed-loop lathes. The roles are distinct and the NCK uses both.

On most turning machines both encoders are wired back to the drive (motor encoder on X311, direct measuring system on X321 on the 6SC6100 / 6SC6500 family) and the NCK reads the position through the drive's serial or parallel position interface. The two are used for:

1. Cross-check: the NCK compares the two actual-position values; if they diverge beyond a tolerance (configured in MD), an alarm in the 25xx range "Position control" or 1040 "Contour monitoring" will fire.
2. Slip compensation: any constant offset between the two is treated as ballscrew torsion / pitch error and compensated, which improves contouring accuracy on turning.

For alarm 1120 the relevant encoder is the motor encoder, because the drive must be able to report speed / position before the brake-release sequence can be confirmed. If the motor encoder is faulty, the drive will not pulse-enable, and the cascade described above follows. Field replacement of the X drive therefore required that the encoder signals be re-checked at the new module's X311 / X321 terminals - a mis-pinned cable produces follow-up alarms 1040 (contour monitoring) or 1680 (encoder defective) rather than 1120, but both are interpreted by the NCK as "axis not safe to move".

Drive Module Replacement: SIMODRIVE 610 / 650 Considerations

On 810T systems the drive is typically a SIMODRIVE 610 or SIMODRIVE 650 module. The replacement must be of the same MLFB (Siemens machine-readable part number) or a clearly listed successor, otherwise the parameter set, current rating, and command structure will not match the original NCK configuration.

When replacing a drive on a 810T GA3:

1. Verify the MLFB exactly. A 6SC6500-0AB and 6SC6500-0AC differ in current rating; a 6SC6100-0AB is a different module than 6SC6100-0BB. Cross-check against the as-built BOM in the cabinet before applying power.
2. Copy the encoder cable pin-out. The X311 (motor encoder) and X321 (optional direct measuring system) pin assignments must match the original. A swapped or crossed pair produces a follow-up alarm (1040 contour monitoring or 1680 encoder defective) and may keep 2000 active.
3. Set the axis address. On dual-axis 6SC6500 modules, the address jumper selects which axis is the master and which is the slave. X should be the master (address 1) and Z the slave (address 2) for the standard 810T topology.
4. Re-load the drive parameters. Drive parameters for 810T are stored on the CCU's battery-backed SRAM; if the battery is weak, parameters may be lost. Verify by entering the drive's parameter menu and comparing against the commissioning sheet.

Hydraulic Interlock and Clamping Circuit Diagnostics

The "hydraulics won't come on" symptom must be diagnosed in this order, because the hydraulic start is gated by the E-stop chain and by axis controller-enable logic on most 810T lathes.

1. Verify 2000 E-stop is clearable. Reset the E-stop push-button, then attempt an NC reset (CANCEL or RESET key). If 2000 returns immediately, the E-stop chain is still open - go to the chain-tracing section.
2. Verify the hydraulic pump contactor (K0) is pulled in. Listen for the contactor. Use a multimeter on the coil terminals (24 VDC). If 24 V is present and the contactor does not close, the contactor coil is open.
3. Verify the pressure switch. Many 810T lathes have a low-pressure switch on the hydraulic manifold that must close within 2-3 s of K0 pulling in. If the pump runs but the pressure switch does not close, investigate the pump, the relief valve, the filter, and the suction line.
4. Verify the brake-release solenoid. When the NC requests axis motion, the PLC should energise the brake-release solenoid. If the solenoid does not pull in, the brake stays applied, the proximity switch never closes, and 1120 fires within 0.5-1 s of the motion request.

The exact I/O addresses depend on the OEM PLC program. Always refer to the machine builder's PLC source or the commissioning sheet for the canonical addresses on a given retrofit. The naming convention (I33.x, Q41.x) is consistent across most 810T OEM builds, but not universal.

E-Stop Circuit Tracing for Alarm 2000

The E-stop chain on a 810T lathe typically consists of:

1. Hard-wired E-stop push-button (NC contact in series with the safety chain).
2. Cabinet door interlock switches (if used).
3. Drive "ready" relay contact in series - the 6SC6100 / 6SC6500 has a relay contact that opens when the drive is in a fault state.
4. Spindle drive "ready" relay contact.
5. Axis module "pulse enable" feedback.

If the new drive module has not been correctly configured (or its ready-relay contact is wired differently from the original), the safety chain will appear open even though the E-stop push-button is released. The 810T will raise 2000 and refuse all motion. This is the single most common reason that 2000 reappears immediately after a drive replacement.

Field procedure to trace the chain:

1. With the machine powered and E-stop released, measure the E-stop chain voltage at each break point. The chain is typically 24 VDC sourced from a safety relay or from a hard-wired loop. A "low" reading at any segment indicates the break is downstream of that point.
2. Confirm the new drive's "ready" relay contact closes when the drive is in standby. If the relay contact is open, the drive itself is still in a fault state - check the drive's seven-segment display for the active fault code (common codes: F001 overcurrent, F015 encoder, F031 power module, F041 IGBT desaturation).
3. Confirm the door interlocks are closed and that no auxiliary contact is stuck.
4. Confirm the spindle drive "ready" contact is closing. A spindle drive left in a fault state from before the retrofit will also hold 2000 active.

Machine Builder Alarm 6034 - Turret Diagnostic

Alarm 6034 is OEM-defined. To diagnose, you need the OEM PLC source or the OEM's alarm-list PDF. The typical turret ready state machine on a 4-station or 8-station wedge-tool-post or disk-turret lathe is:

1. Turret unclamped (proximity switch 1 made).
2. Turret rotated to the requested pocket.
3. Turret clamped (proximity switch 2 made).
4. Turret "turret_ok" flag set in the PLC status word (and visible to the NCK as bit 7 / 6 in the axis / channel status word).

On a machine held in 2000 E-stop, the PLC processing of the turret may be suspended, leaving the "turret_ok" flag cleared. This is why 6034 appears alongside 2000 - it is a downstream symptom, not an independent turret fault. Clear 2000 first, then re-evaluate 6034.

If 6034 persists after 2000 is cleared, the actual turret is suspect. Investigate:

• Turret rotation motor contactor and overload.
• Turret clamp / unclamp solenoid(s).
• Turret encoder or proximity switches (count, index, clamped).
• Tool table mismatch between PLC and NCK (compare tool pocket numbers in the tool table with the PLC's expected mapping).

Step-by-Step Diagnostic and Repair Procedure

The following procedure assumes the drive has been replaced. If it has not been replaced, do that first, observing the notes in the previous section.

1. Power down completely. Main disconnect off, wait 5 minutes for the DC link to discharge. Lock-out and tag-out per site safety rules.
2. Inspect the new drive's part number and parameter label. Verify the MLFB matches the BOM. If the label is illegible or missing, treat the drive as suspect and source a known-good unit.
3. Re-check the encoder wiring at the new drive. X311 (motor encoder) and X321 (direct measuring system) pin-for-pin against the original wiring diagram. Use a multimeter on the encoder cable to verify continuity end-to-end (each pair, plus shield continuity to chassis ground at one end only).
4. Re-check the drive address jumper and bus termination. On a 6SC6500 dual-axis module, the master / slave jumper must match the X = master, Z = slave configuration.
5. Re-check the "ready" relay contact wiring. Confirm the new drive's relay contact is wired into the E-stop safety chain at the correct terminal - this is the most common cause of post-replacement 2000.
6. Apply power, but do not enable drives yet. Observe the 7-segment display on the new drive. It should reach standby state (e.g., "0" or blank) without showing a fault code.
7. Bring up the operator panel. If the panel does not boot, check 24 VDC at the OP, the ribbon cable, and the backlight fuse. If still no display, perform an NCK cold restart (described below).
8. Clear the alarm stack. Use the CANCEL / RESET keys to clear the visible alarms. If 2000 re-appears, the E-stop chain is still open - go back to the chain-tracing section.
9. Confirm the hydraulic pump starts. If it does not, verify Q40.0 (or the equivalent PLC output) is being driven, K0 contactor coil is receiving 24 V, and the contactor is closing. Then verify the pressure switch closes within the configured time.
10. Try a manual axis motion in JOG. Select the X axis, attempt a small jog. The NCK will request the brake release. Verify the brake-release solenoid is energised (Q41.0 or equivalent), the brake physically releases (you should hear a soft click and see the slide move), and the clamp-confirmed input (I41.0 or equivalent) transitions to the released state within 0.5-1 s.
11. Approach the reference point. With both axes responding to JOG, perform a G74 / reference approach. The 1120 alarm should not recur. If it does, the clamp-confirmed input is not reaching the NCK - re-trace from the proximity switch to the PLC input card to the NCK-PLC interface.
12. Run a dry part program. Single-block, dry-run, no coolant. Confirm spindle, turret, and axes all behave as expected. Then a full program with the part loaded.

Verification, Commissioning, and NC Reset

Verification on a SINUMERIK 810T GA3 follows a standard sequence. The matrix below is the canonical commissioning checklist for the fault class described here.

If a full NCK cold restart is required, power down the NCU / CCU, hold the CANCEL key during power-up, and continue to hold until the NCK requests the cold-start confirmation. Then confirm. This is necessary when the alarm stack is corrupted or when the battery-backed SRAM has lost machine data. The same procedure is used to recover from a soft PLC fault after a drive module replacement.

Preventive Maintenance Schedule

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