Troubleshooting S7-417 CPU Diagnostic Event 16#3583 Memory Errors

1. Fault Scenario Overview

The S7-417 / CPU 414-4H is the high-availability redundant controller in the SIMATIC S7-400 family. When the diagnostic buffer accumulates repeated entries with the event ID 16#3583 and the requested OB is OB84 (CPU hardware fault), the system is reporting a hardware-level memory integrity problem. The standard buffer entry in this class typically reads:

Event ID 16#3583 — Accumulation of detected and corrected memory errors. Requested OB: CPU hardware fault OB (OB84). OB not found, or disabled, or cannot be started in the current operating mode. Internal error, incoming event. Internal RAM or internal flash with the operating system.

The recommended Siemens field action is to evaluate the OB84 environment, isolate the affected subsystem (CPU, PS 405, or backplane), and replace the failing component. This article decodes the event, maps it to the underlying S7-400 hardware/firmware behavior, and walks through a complete diagnostic-to-replacement procedure that fits a redundant H-system.

2. Affected Hardware and Firmware Reference

The diagnostic buffer entry "Rack: 0 Slot: 3" corresponds to a CPU in the central rack. In an H-system, both racks (rack 0 and rack 1) are monitored independently; the same event from the standby CPU confirms a hardware-level issue affecting the operating system storage rather than a transient communication fault.

3. Decoding Event ID 16#3583

Siemens assigns a fixed meaning to each diagnostic event ID. The full set of IDs is published in the STEP 7 System and Standard Functions reference manual; relevant excerpts for this case are summarized below.

Event 16#3583 is the "accumulation" event — meaning single-bit corrections have crossed a threshold inside the firmware's error counter. Once accumulated, the firmware raises a non-recoverable OB84. The associated Z1 status word f802 in the buffer entry is the S7 internal status code; combined with the OB84 not-found/disabled note, it indicates the error class reached its terminal state before the user OB could intercept it.

4. OB84 — CPU Hardware Fault Organization Block

OB84 is invoked by the S7-400 firmware when it detects an internal CPU error, an error in the operating system execution, or — as in this case — uncorrectable memory errors. Behavior depends on configuration:

For a CPU 414-4H, OB84 is the canonical entry point for hardware-fault-triggered redundant switchover. The H-system firmware (F-system link with the active partner) can execute a take-over if OB84 is configured to call SFC 90 (H_CTRL) or if the redundancy error OB (OB72) is wired in parallel. If OB84 is missing, the failing CPU cannot initiate a clean switchover and the partner CPU remains in standby — production halts.

4.1 Required OB set for H-mode diagnostics

• OB70 — I/O redundancy error
• OB72 — CPU redundancy error (H-specific)
• OB81 — Power supply fault
• OB82 — Diagnostic interrupt
• OB84 — CPU hardware fault (this event)
• OB85 — Program execution error
• OB121/OB122 — Programming / I/O access errors

Verify all are loaded in the active and standby CPU project; the failing unit's buffer noting "OB not found or disabled" is a strong indicator that the standby CPU image has incomplete OB loading — typical after a partial project update or a memory-card swap that did not include the system data blocks.

5. Root Cause Map: Memory, Power, or Sync?

Three subsystems can produce OB84-class memory error entries on the CPU 414-4H. The buffer text alone cannot distinguish them; the diagnostic procedure must.

A documented field case in the S7-417-4H community: an installation experienced full CPU drop-out; the PS 405 indicator LED was OFF. After unplugging and reseating the power connector to the CPU, the system started normally with no further events. This shows the same OB84-class symptom (CPU appears to fail) can be triggered by intermittent power-supply contact, not by RAM aging. The first diagnostic step is therefore to differentiate power vs. memory before ordering a CPU replacement.

6. PS 405 Power Supply Failure Mode

The PS 405 (10 A: 6ES7 405-0KA02-0AA0; 20 A: 6ES7 405-0RA01-0AA0) feeds 5 V and 24 V to the S7-400 backplane. If the 24 V input to the PS 405 dips below its regulation threshold (typically below 19.2 V on wide-range units), the PS 405 de-asserts its DC OK signal and the CPU's BATF/EXTF LEDs illuminate. The CPU may log 16#39xx events or, if the dip is fast, OB84-class memory errors because the flash write in progress was aborted.

6.1 PS 405 Voltage Checks

1. With PS 405 powered, measure output at the backplane 5 V test point: must be 5.10 V ± 2 % (4.998–5.202 V).
2. Measure 24 V output: 24 V ± 5 % (22.8–25.2 V) for backplane use, regulated.
3. Measure input 24 VDC at PS 405 terminals: must remain above 19.2 V under full load dip.
4. Check ribbon cable connector between PS 405 and backplane: reseat, look for bent pins, oxidation.

7. Diagnostic Procedure — Step by Step

7.1 Prerequisites

• STEP 7 V5.5 SP4 (or TIA Portal V15.1+ with S7-400H package) installed on the engineering station.
• Ethernet or MPI/DP cable to the CPU's PG port.
• Online access to the affected CPU with at least Monitor privilege.
• STEP 7 "PLC → Online → Diagnostic Buffer" reachable.
• Spare PS 405 and (if budget allows) a spare CPU 414-4H with the same firmware V4.0.7 (or compatible V4.0.x) on hand.

7.2 Procedure

1. Open the diagnostic buffer on both CPUs of the H-system: PLC → Online → Accessible Nodes → right-click CPU → "Online & Diagnostics" → "Diagnostic Buffer". Export the buffer as .txt for archival.
2. Filter for event IDs in the ranges 16#3500-16#35FF (memory), 16#3900-16#39FF (power), and 16#7300-16#73FF (H-link). Count how many 16#3583 events are present within 24 hours and 7 days.
3. Read the OB84 configuration on the failing CPU: PLC → Online → Accessible Nodes → CPU → "Hardware Diagnostics" → "OB Configuration". Verify OB84 is loaded and contains your fault handler. If "not loaded", the event is non-recoverable from a software standpoint.
4. Read the LED pattern on the CPU: STOP steady, RUN blinking, EXTF on, BUSF1/2 off, REDF (redundancy fault) on for H-system.
5. Measure the backplane voltages as in section 6.1. If out of tolerance, replace PS 405 and re-evaluate — do not proceed to CPU replacement yet.
6. Reseat the power connector to the CPU even if voltages are correct. The connector can develop high resistance under thermal cycling, producing the same symptom.
7. Power-cycle the CPU (turn PS 405 OFF for 30 s, then ON). Watch the diagnostic buffer; if 16#3583 re-appears within 1 hour of operation, the RAM/flash is degraded.
8. Check the H-link — if the partner CPU was in standby and never took over, the sync modules and fiber may be the underlying issue. The standby CPU should have logged 16#73A1 (link-down) or similar. If yes, the H-link is the problem, not memory.
9. If memory is confirmed as the root cause, schedule a CPU replacement window. Plan a full project download onto the new CPU, including all OBs, FBs, FCs, DBs, and the system data (SDB) container — OB84 inclusion is mandatory.

8. CPU Replacement Procedure (H-System)

The CPU 414-4H supports hot-swap redundancy only with a healthy standby partner. The sequence below preserves process state.

1. Confirm the standby CPU is in RUN and LINK LEDs are green on both sync modules.
2. From STEP 7, online-monitor the active CPU's H-status: H-STCTRL should show SINGLE or REDUNDANT with the partner in STANDBY.
3. Take a backup of the active CPU: PLC → Upload to PG the entire project including SDBs. Save to a memory card image.
4. Power down the failing CPU's PS 405 (the one in the affected rack, slot 3).
5. Remove the memory card from the failing CPU; insert it into the new CPU of the same order number and firmware version.
6. Insert the new CPU into the same slot. Power up the PS 405.
7. The new CPU will boot from the memory card and attempt to link with the active partner. The H-system performs an Update synchronization; the new CPU becomes the standby.
8. Verify event buffer on the new CPU shows a clean startup and no 16#3583 events within 30 minutes of operation.
9. Run a manual switchover: from STEP 7, force an H-switchover via H_CTRL or the online H-Panel. The previously failing CPU (now replaced and standby) takes over; the formerly active CPU becomes standby. Confirm process continues with no loss.

9. Verification Checklist

10. Firmware Compatibility Notes

CPU 414-4H order number 6ES7 414-4HJ04-0AB0 ships with firmware V4.0.7. Hot-spare units must carry the same major firmware version; mixing V4.0.x with V4.5.x is not supported in H-mode. Before ordering a spare, confirm:

• Order number suffix matches -0AB0 (H-variant).
• Firmware version on the replacement label is identical to the active partner.
• The STEP 7 hardware catalog entry for the replacement is at the same ES (engineering state) — mismatches block online downloading.

Siemens typically bundles firmware as a separate package (F-CPU FW Update) on the support portal. Use only the official Siemens firmware update tool; field updates with third-party tools are not supported and can cause permanent OB84 corruption.

11. Common Pitfalls

• Replacing the CPU when PS 405 is the fault. Always measure backplane voltages first; a reseat of the power connector restores operation in a documented fraction of S7-417H cases.
• Forgetting OB84 in the project download. After a replacement CPU is inserted, the new CPU must be re-loaded with the full project, not just the user program. SDBs contain the OB priority and event mask settings.
• Mixing H-mode and stand-alone mode. A CPU 414-4H can run solo, but the partner CPU image will not exist. If OB84 fires in solo mode, no switchover is possible — manual CPU replacement is required immediately.
• Ignoring the memory card. The memory card on the failing CPU may be the actual source of corruption. Test it in a known-good CPU before declaring the new CPU "good".
• Skipping the H-switchover test. A system that has never been tested under switchover may fail in the first real redundancy event. Run a planned switchover at every major maintenance window.

12. FAQ