Scope of this technical record
Fault/symptom page for a Starvert iS5 auxiliary supply whose nominal 24 V rail is dangerously elevated or unstable, based on the SV185iS5-4N0 case.
A 24 V control path rising to approximately 56 V can cause additional controller destruction. Do not expose a known-good CPU board while this fault remains unresolved.
Why this is not a normal no-power fault
A dead auxiliary supply typically prevents control electronics from operating. This failure is more dangerous: the supply operates outside regulation and can feed excessive voltage into circuits that technicians may be trying to save. In the documented SV185iS5-4N0 unit, the rail identified as 24 V reached approximately 56 V, while other output groups also increased and fluctuated.
Because the CPU board had already failed, fitting a replacement before measuring the supply led to a second board loss. The correct technical interpretation is therefore control-supply overvoltage with downstream damage risk, not simply “CPU board bad.”
Evidence-led diagnosis
When multiple secondary rails are high or unstable together, the diagnostic boundary moves upstream to regulation and feedback. The case investigation focused on secondary sampling and the circuit surrounding the component marked ZD13. A 431-type precision reference interpretation was supported by the circuit context and by a measured node around 2.5 V.
R50 provided the decisive evidence. It was intended to be 2.61 kΩ, yet readings intermittently rose above 10 kΩ or moved significantly under measurement. After removal, one lead was found physically fractured from the resistor body. Replacing it with a 2.61 kΩ SMD resistor restored stable output voltages.
Overvoltage triage boundary
| Finding | Do not conclude | Next responsible route |
|---|---|---|
| CPU board damaged | Replacement board alone will solve fault | Verify supply rails first |
| 24 V significantly high | Individual output load is the only suspect | Inspect regulation/feedback |
| Resistance changes under probing | Meter is merely unreliable | Remove and inspect suspect SMD part |
| Rails stable after feedback repair | All drive functions automatically proven | Proceed with controlled control/power-stage evaluation |
Repair decision and commercial intent
This type of query has strong repair intent: the owner has an obsolete or difficult-to-source industrial drive and has already experienced expensive collateral damage. A high-quality technical page should help distinguish three needs: component-level power-supply repair, replacement CPU-board qualification after supply proof, or full-drive exchange/retrofit where downtime or parts risk is too high.
IndustrialDriveData should not offer a CPU-board replacement based solely on a symptom description. The qualified request needs measured rail evidence, prior damage history and board photographs so a service provider can price the correct work rather than repeat the failure.
Differentiating an overvoltage rail from a failed load
A shorted load and a loss-of-regulation fault are not equivalent. A shorted load usually drags a supply down or invokes current limiting; the documented iS5 event drove multiple rails upward and unstable. That behaviour makes feedback sampling, the precision reference region and its continuity more relevant than immediately hunting for each downstream load fault.
This distinction is practical because control boards are expensive and increasingly difficult to replace in a discontinued drive. Where a nominal 24 V supply is far above tolerance, a replacement board should be treated as endangered property, not as a diagnostic tool.
Evidence package for remote diagnosis
A remote support request should record the meter reference point, condition during measurement, 24 V behaviour over time, any other available auxiliary rails, photos of the ZD13/R50 area and whether the CPU board was attached during the event. It should also state whether the IGBT power stage was previously damaged.
Those items distinguish an ordinary spare-part inquiry from a board-level repair case. They allow a technician or service partner to decide whether control-board sourcing is sensible, whether the supply board should be repaired first, or whether the whole discontinued drive is a better exchange candidate.
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.
Documents the 24 V rail rising to approximately 56 V, ZD13/R50 feedback diagnosis and restored stable outputs.
Family, model, wiring and fault-history context for Starvert iS5.
Confirms model-market identity, rating context and discontinued-product supply signal.