Identifying Siemens 6SE70 PSU1 vs PSU2 Replacement Cards Safely

Field failures involving Siemens Simovert Masterdrives (6SE70 series) frequently trace back to power supply (PSU) card confusion. The drive family uses two electrically distinct internal power supply boards, designated PSU1 and PSU2, with catalog numbers that differ only in the final suffix character. Cross-installing a PSU1 into a PSU2 slot — or vice versa — can produce immediate catastrophic failure that propagates downstream into the CUVC control board, CBP2 Profibus communications card, and SLB fibre-optic (SIMOLINK) interface. This reference explains how to verify the correct PSU catalog number before power-on, how to read the 6SE70 designation, and how to recover a drive where an incorrect PSU has been installed.

1. Problem Definition: PSU Card Cascade Failure

A 6SE70-412W.6 drive was reported with the following fault progression:

1. Original PSU2 board (catalogue 6SE7038-6GL84-1JA1) exhibited contamination symptoms consistent with moisture ingress.
2. A replacement board of the same catalogue number (6SE7038-6GL84-1JA1) was sourced but on visual inspection differed physically from the original.
3. On first power-up of the replacement, the board drew excessive current, smoked, and the failure propagated through the backplane, taking out the fibre-optic interface card and the Profibus card attached to the CUVC.

Root cause analysis of the returned card revealed that the supplier had shipped a PSU1 (catalogue 6SE7038-6GL84-1JA0) by mistake. The PSU1 and PSU2 boards are functionally similar — both generate the internal +5 V, +15 V, and -15 V rails from the DC-link — but they are not pin- and rail-compatible substitutes. The output rail set, isolation, and load-share resistor networks differ between the two designs.

2. Siemens 6SE70 Designation Breakdown

Understanding the 6SE70 order code prevents mis-ordering and accelerates replacement. Each block encodes a specific attribute:

The full drive order code 6SE70-412W.6 decodes as follows for the host drive:

3. PSU1 vs PSU2 — Functional and Physical Differences

Both boards are switch-mode power supplies fed from the DC-link. They generate the auxiliary rails used by the CUVC, CBP2, and SLB option cards. The differences are not always apparent from the silkscreen alone, so catalogue number verification is mandatory.

4. Pre-Replacement Verification Procedure

1. Isolate the drive. Open the upstream circuit breaker and wait for the DC-link to discharge below 50 V DC. Confirm with a CAT III 1000 V meter on the DC+ and DC- terminals. The internal discharge resistor requires a minimum of 5 minutes after isolation on 400 V class units.
2. Verify the failed board's catalog number. Read the silkscreen label on the faulty PSU. Note that the barcode label may differ from the silkscreen if a reworked board was returned from a service depot.
3. Match against the drive's configuration record. Cross-reference the BOM (bill of materials) and the drive nameplate data set (P070 parameter readout) before ordering any replacement.
4. Inspect the new board on receipt. Before bag-opening, photograph the part number, revision, and ESD seal. Reject any board whose catalogue ends in -1JA0 when a PSU2 was ordered, or vice versa.
5. Bench-precondition. Place the new board on an antistatic mat and visually inspect solder joints, electrolytic capacitors, and any signs of liquid ingress or reflow rework.
6. Anti-static precautions. Use a wrist strap bonded to the drive chassis. PSU boards include CMOS gate-driver devices sensitive to >100 V ESD discharges.

5. Replacement Procedure

1. Remove the option-slot cover plate to gain access to the PSU retention screws.
2. Disconnect all ribbon and power cables from the failed PSU. Label each connector with masking tape.
3. Remove the two M3 retention screws securing the PSU to the chassis backplane.
4. Slide the PSU straight out using the extraction tabs. Do not rock the board — the multi-pin connector at the rear is rated for axial insertion force only.
5. Compare the new board against the old one side-by-side: connector count, silkscreen revision, capacitor polarity stripe.
6. Insert the replacement PSU2 (6SE7038-6GL84-1JA1) with the same axial alignment as the removed unit.
7. Tighten the retention screws to 0.6 Nm. Do not exceed 0.8 Nm — over-torque cracks the PCB.
8. Reconnect ribbon cables per the tape labels.
9. Re-fit the option-slot cover plate.

6. First Power-Up After PSU Replacement

1. Close the cabinet door. Verify cabinet fans rotate on the 24 V control supply before applying main power.
2. Apply the 400 V three-phase supply through the upstream breaker.
3. Listen for the soft-click of PSU2's inrush limiter — if no click within 2 seconds, de-energise immediately.
4. On the CUVC operator panel (PMU), observe the boot sequence: the display should show "rdy" or "run" depending on parameter r001.
5. Read parameter P070 and confirm it matches the drive's nameplate value recorded at the start of this procedure.
6. Read fault buffer parameters r947 / r949 and clear with the PMU keypad sequence if any historical faults persist.
7. Run the drive unloaded with a slow speed reference of 5 % to validate encoder feedback, CUVC heartbeat, and option-card recognition.

7. Damage Assessment After Wrong PSU Installation

When a PSU1 is installed in a PSU2 slot, the +15 V rail rises to approximately +24 V within milliseconds. This overvoltage is coupled onto the CUVC backplane and propagates into every option slot. Typical failure pattern:

8. Recovery Steps After Cascade Damage

1. Document the incident. Photograph the smoked board, the damaged slots, and the cabinet nameplate. Record the time, ambient humidity, and any recent water-ingress events.
2. Replace the PSU first with the verified correct catalog number (-1JA1).
3. Replace the CUVC if the PMU is dead or the drive does not boot after PSU replacement. Re-load firmware via DriveMonitor / STARTER before commissioning.
4. Replace the Profibus (CBP2) and fibre-optic (SLB) cards. Re-set their node addresses (DIP switches) and baud-rate configuration before re-attaching to the network.
5. Inspect backplane connectors for carbon tracking between pins. If carbon deposits are visible, replace the backplane or send the chassis to a Siemens-certified repair centre.
6. Validate insulation resistance with a 500 V megohmmeter between DC+ and earth, then DC- and earth. Minimum acceptable: 1 MΩ. Anything below 50 kΩ indicates further damage and mandates transformer / cable meggering.
7. Recommission per Section 6.

9. Diagnostic LED and Fault-Code Matrix

Use this matrix when triaging a 6SE70 with suspected PSU-related faults:

10. Verification Checklist Before Returning to Service

• PSU2 catalog number on silkscreen matches 6SE7038-6GL84-1JA1.
• PSU1 catalog number (if fitted) matches 6SE7038-6GL84-1JA0.
• PMU displays "rdy" within 5 seconds of power-on.
• P070 matches the drive nameplate.
• Fault buffer (r947) empty after first no-load run.
• CBP2 visible to Profibus master with configured node address.
• SLB green LED steady when SIMOLINK master is broadcasting.
• Insulation resistance > 1 MΩ on DC+/DC- to earth.
• Cabinet IP rating restored (gaskets, desiccant, cable glands).

11. Spare-Parts Stocking Recommendations

Maintain a minimum on-hand quantity of PSU2 boards calibrated to the drive fleet population. For sites with more than ten 6SE70 drives, stock at least two spare PSU2 units pre-validated by serial number. Label each spare with its verified catalog number and date of receipt — never store a PSU1 in a location labelled "PSU2 spare" because the visual ambiguity is the root cause of the cascade failure mode documented here.

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