Troubleshooting Siemens C7 633 HMI F1-F4 Function Key Failures

System Overview: Siemens C7 633 Integrated Controller

The Siemens C7 633 (Siemens catalog family 6ES7633-...) is a Compact Controller that combines an S7-300 CPU 315-2 DP logic module with an OP7 operator panel inside one housing. It is frequently deployed in mid-size machine control applications where panel space is constrained but full PLC functionality is still required. The product integrates two distinct engineering domains: STEP 7 / SIMATIC Manager for the PLC side and ProTool / ProTool/Lite for the OP7 HMI side.

Because the controller ships as one physical unit but logically behaves as two devices, every programming action has to be performed with the correct tool, the correct cable, and the correct interface. When a customer replaces the internal backup battery, performs a re-download, or commissions a replacement unit, several edge-case failure modes can disable the OP7 function keys (F1, F2, F3, F4). This article consolidates field-tested diagnostics and corrective procedures for the symptom: "after re-download, HMI shows error and F1 to F4 are not working."

Problem Description

The reported symptom occurs in this typical sequence:

1. The backup battery inside the C7 633 ages or fails.
2. The customer replaces the battery while power is removed (which clears retentive RAM) or while the program is lost.
3. The Siemens service center uploads or re-uploads the program.
4. After upload, the HMI displays an error banner (commonly "OP7 / Communication Error", "Project Not Found", or "Wrong Project Version") and the F1-F4 function keys stop responding.

Function keys F1-F4 on the OP7 are the only operator input keys for soft-key navigation and bit-triggered control actions. When the F-keys fail, the operator cannot acknowledge alarms, toggle screen views, or trigger the discrete outputs bound to them in the ProTool project. Machine operators can be locked out of the application.

Root Cause Analysis

Field experience with the C7 633 indicates seven primary root causes for F1-F4 failure after a re-download. Each must be ruled out systematically.

The service-engineering remark that the C7 633 is "a combination of CPU 300 and OP7" is technically precise and directly explains why a single re-download is insufficient. Always treat the two halves as independent commissioning tasks.

Diagnostic Procedure

Execute the following diagnostic sequence before changing any wiring or project files. Each step produces a verifiable answer that drives the next decision.

1. Power down and reseat the Memory Card. Power off, remove the C7 633 lid, and confirm that the Memory Card (Flash EPROM, 5 V) is fully seated. A partially inserted MC after a battery swap is the single most common field fault.
2. Verify CPU state via LEDs. Apply power. CPU 315 SF, BF, DC5V, FRCE and OP7 status LEDs must show normal operating pattern (no continuous SF, no BF).
3. Connect via PG cable. Use the USB PC Adapter (6ES7972-0CB20-0XA0) or the legacy PC/MPI adapter (6XV1440-2K...). Set PG/PC interface to "PC Adapter (MPI)" at 187.5 kbps.
4. Read OP7 system menu. Hold the two soft keys together while powering on, or follow the OP7 DP "System / Backup / Restore" navigation to verify the OP7 project is present.
5. Read CPU online with STEP 7. Open SIMATIC Manager, go online, and verify block consistency, project version, and Memory Card content. Compare to the original archive.
6. Trigger F-key bit test. Force the F-key assignment bit (commonly M0.0-M0.3, or a defined bit in the area pointer DB) in the PLC. If the operator screen reacts, the wiring and OP7 input layer are healthy and the failure is on the configuration side.

Step-by-Step Resolution

Step 1 - Restore PLC Program from Archive

1. Open the customer's archived STEP 7 project on the programming PG.
2. Confirm the project version, block timestamps, and hardware configuration match the unit on the bench.
3. Connect PG to the MPI port on the C7 633 front panel.
4. Use SIMATIC Manager: PLC > Download to Programming Device / CPU, select "Download to Target Device."
5. After download completes, go online and verify that all blocks are present and consistent.

Step 2 - Restore OP7 Project from ProTool Archive

1. Open the matching *.pdb ProTool project file from the customer's archive.
2. Validate project > OP version against the physical OP7 DP firmware (typically V5.x or V6.x).
3. Disconnect the PG cable from the PLC MPI port and reconnect it to the OP7 service port (top of panel).
4. In ProTool: File > Download > select COM port, baud 187.5 kbps, MPI address (default 1 for OP7, default 2 for CPU).
5. Send the project. Wait for the OP7 to reboot and display the start screen.

Step 3 - Re-establish Area Pointer / Bit Assignments

The OP7 communicates with the CPU 315 via configurable area pointers. For F-key bit assignments, verify these items in ProTool:

If the customer originally added a "F1-F4 button modification" after initial commissioning, the modification must exist in the ProTool source. A common field fault is uploading only the original *.pdb from the engineer but not the modified version with the F-key event bindings.

Step 4 - Insert Memory Card and Restore

1. Power off the C7 633.
2. Insert the Memory Card (5 V Flash EPROM) with the program images.
3. Power on. CPU should boot from MC. Verify with PG online: PLC > Save / Restore > view Memory Card contents.
4. If MC was blank, perform a fresh download to MC: PLC > Save to Memory Card.

Step 5 - Verify F-Key Operation

1. Navigate to a screen with F-key labels visible.
2. Press each F-key. The corresponding tag bit in the PLC must toggle within 100 ms (OP7 polling interval is typically 100 ms).
3. Use VAT or a watch table to observe the bit transitions live.

Hardware Verification

If a tactile inspection reveals a stuck or damaged key, the OP7 DP keypad must be replaced as a subassembly (Siemens part 6AV3637-1LL00-0AX0 keypad foil). Membrane failures can mimic configuration failures.

ProTool Software Configuration

The OP7 DP is configured in ProTool or ProTool/Lite. For a service restoration, the original *.pdb file is the source of truth. If the original file is missing, manual reconstruction is required using these ProTool fields:

• Screen hierarchy and number of base screens (OP7 supports up to 999 screens, 4 lines x 20 chars).
• Tag database with correct DB / byte / bit addresses.
• Area pointers: Coordination, F-Keys, Status, Curves (if used).
• Alarm messages linked to bit triggers in the PLC.
• Language tables (OP7 supports up to 5 languages; Chinese tables require firmware V5.5 or later).

Memory Card and Backup Procedures

The Memory Card (MC) on the CPU 315 serves as both program storage and retentive archive. The recommended backup workflow after every firmware / project change is:

1. In SIMATIC Manager: PLC > Save to Memory Card.
2. Insert a blank, pre-formatted Flash EPROM MC.
3. Confirm successful save (green LED, message "Save successful").
4. Physically label MC with project name, version, date, and PG operator initials.
5. Store the MC in an antistatic case in the same cabinet for hot-swap recovery.

If a customer reports F-keys failing after a battery event but the MC is intact, the program is on the MC but not loaded to work RAM. Perform PLC > Copy RAM to ROM, or remove and re-insert the MC to force a boot from card.

Firmware and Version Compatibility

If the OP7 firmware was upgraded without recompiling the *.pdb project, F-key event handling can break silently. Always recompile the project after any firmware change.

Cable and Interface Setup

Two cables are relevant to C7 633 commissioning:

• USB PC Adapter (6ES7972-0CB20-0XA0): Current recommendation. USB-A to RS485 MPI/Profibus, 1.5 m. DIP switch sets bus termination and 24 V DC backplane tap.
• Legacy PC / MPI Adapter (6XV1440-2Kxx): RS232-to-MPI conversion. Still functional but obsolete. Older field installations may still rely on this cable for ProTool download to the OP7.

Verify the cable is plugged into the correct port for the device being programmed:

• PLC program: MPI port on CPU front panel.
• OP7 project: Service port on top of the OP7 panel.
• If the wrong port is used, ProTool will time out at 187.5 kbps after approximately 30 seconds with error 0xE0FE (bus fault) or "Node not found".

Error Code Reference

Common OP7 and ProTool error messages encountered during the F-key failure case:

Verification Checklist

Confirm each item before closing the service ticket:

• Power cycle with MC inserted restores program from MC.
• STEP 7 online shows all blocks green, no timestamp mismatch.
• ProTool online shows current OP7 project version matches *.pdb.
• Each F1-F4 press triggers its bound tag bit within 100 ms.
• Alarm acknowledge via F-key clears the alarm in STEP 7 diagnostic buffer.
• Battery voltage measured > 3.5 V DC at terminals.
• MC labeled and stored; original *.pdb archived on PG and network share.

Preventive Recommendations

1. Always replace the backup battery with the C7 633 powered (hot-swap) so that work RAM is retained and a re-download is unnecessary.
2. Keep the *.pdb, *.s7p, and the MC as a triple archive at every site visit.
3. Document any customer-initiated F-key modification in the project so that the original *.pdb remains the recovery source.
4. Schedule battery replacement every 5 years (typical 3.6 V lithium life at 25 C).
5. Train customer maintenance on the dual-processor nature of the C7 633 to prevent single-side re-downloads.

FAQ