Scope of this technical record
Exact model reference for the LG / LS SV185iS5-4N0 unit involved in a documented switching-power-supply and repeat CPU-board damage repair case.
Do not use a donor CPU board or run command as a test instrument for an unverified auxiliary supply. High or unstable rails may damage replacement electronics instantly.
Model identity and repair relevance
SV185iS5-4N0 belongs to the Starvert iS5 400 V class. Product references identify the associated 25 HP / 18.5 kW frame context and a three-phase 380–460 V AC input range. Market listings indicate that this model is discontinued yet remains present in repair and replacement channels, which makes a reliable repair record materially useful.
The model is important to the database because a concrete repair case exists at component level. The unit initially arrived with IGBT damage and a damaged CPU board. After a repair attempt, the CPU board failed again. Investigation then found that the nominal 24 V supply rose as high as approximately 56 V, with other low-voltage outputs also high and unstable.
What the evidence establishes
The documented evidence does not justify claiming that every SV185iS5-4N0 CPU failure has the same root cause. It does establish a critical diagnostic rule: after destructive power-stage and CPU damage, the control-power supply must be considered unsafe until its rails and feedback regulation have been proven.
The repair investigation examined the device identified on the board as ZD13, marked only “4.” By analysing its surrounding circuit and measured behaviour, the repairer identified it as being in a 431-type precision regulation context. The key failure was found at R50: a nominal 2.61 kΩ SMD resistor whose lead had fractured from its body and produced unstable readings.
Case evidence record
| Observation | Documented finding | Diagnostic value |
|---|---|---|
| Initial damage | IGBT and CPU board damaged | Triggers cascade analysis |
| After attempted repair | CPU board damaged again | Do not keep substituting boards |
| Supply measurement | 24 V rail up to about 56 V; other outputs high/unstable | Investigate supply regulation |
| Feedback inspection | R50 fractured; nominal 2.61 kΩ | Mechanical SMD damage can be hidden |
| After replacement | Outputs stable | Supply proven before further controller work |
What to collect before a repair or replacement request
A model-specific inquiry should include the complete label suffix, photos of the CPU/power board and connector positions, details of any replaced IGBT or CPU board, and the measured behaviour of the low-voltage supplies. Without that evidence, an exchanged board could be exposed to the unresolved supply fault.
A buyer seeking a used or refurbished complete drive should also preserve the existing parameter and application context before replacement. The board-level route in this page is intended for repair triage; equipment substitution may require commissioning and motor/application checks beyond this record.
Relationship between rating, frame and repair evidence
The repair record must remain tied to the exact model because the iS5 family spans multiple power levels and frame arrangements. Published iS5 documentation places SV185iS5-4 within the 25 HP class, alongside SV220iS5-4 at the next rating in the same general frame group. This establishes product identity; it does not automatically establish that a CPU-power board from another rating or revision is interchangeable.
For workshop intake, the model code should be paired with visible PCB labels and connector positions. A replacement proposal based on “iS5 18.5 kW” alone is weak where the failure involves a supply board and downstream controller electronics: board revisions, previous repair changes and missing components can materially change the risk of energising the unit.
Repair acceptance criteria
A repaired SV185iS5-4N0 should not be considered ready merely because a keypad powers or an output module has been fitted. Before functional testing, the service record should show stable control rails, absence of visible carbonisation or reworked feedback damage, and a clear account of which controller and power-stage assemblies were connected during validation.
This page therefore supports two different users: a technician who needs the correct diagnostic boundary, and a plant owner who needs to know why “replace the board” is not a reliable quotation unless the power supply that feeds it has first been proven safe.
Field record checklist
- Capture full model and board evidence
- Verify control-supply rails before replacement testing
- Record previous destructive failure history
Technical basis and reference documents
This is an independent editorial technical reference. Original manufacturer documentation remains controlling for installation, repair and commissioning decisions.
Family, model, wiring and fault-history context for Starvert iS5.
Documents the 24 V rail rising to approximately 56 V, ZD13/R50 feedback diagnosis and restored stable outputs.
Confirms model-market identity, rating context and discontinued-product supply signal.
Related technical records
A repaired LG / LS SV185iS5-4N0 shows abnormal or unstable low-voltage supplies; the nominal 24 V control rail may rise far above normal and endanger connected control electronics.
An iS5 drive initially presents with power-stage and CPU-board damage; after apparent repair and test power-up, the CPU board fails again.
A reconstructed functional path for the SV185iS5-4N0 case: switching transformer outputs feed control rails while an optical feedback/reference network, including the ZD13/R50 branch, regulates the secondary supply level.
Maps the documented cascade in which initial IGBT and CPU damage was followed by a second CPU-board loss because the low-voltage supply had not yet been proven safe.
SV185iS5-4N0 has suffered IGBT/CPU damage or presents unstable low-voltage rails; the 24 V control supply is suspected of rising above its intended level.
An iS5 drive has destroyed a CPU/control board after IGBT repair or a donor CPU board is being considered for testing.