A TSW101 installed in transit vehicles becomes unresponsive during vehicle startup while all occupied-port LEDs flash synchronously in a repeating pattern. A hard power cycle restores operation. The same failure occurs with a Rosho 8s switch, so the evidence does not isolate the TSW101, its firmware, or a single switch batch as the root cause.
Confirmed Symptoms and Test Results
| Observation or test | Result | Engineering implication |
|---|---|---|
| Vehicle startup | Switch freezes and occupied-port LEDs flash synchronously | The failure is associated with startup, but the evidence does not distinguish a boot loop from repeated PoE protection operation. |
| Hard power cycle | Restores operation | The failure is recoverable but requires interruption of switch power. |
| Startup delay | A 15–30 second delay after ignition did not prevent the failure | A delay alone does not correct the triggering condition. |
| Rosho 8s substitution | Produces the same flashing and freeze | Investigate conditions shared by both installations before treating this as a TSW101-only defect. |
Root-Cause Boundaries
The synchronous LED pattern could represent repeated startup, PoE protection activity, or another shared reset condition, but the available evidence does not identify which state is occurring. No input-voltage trace, PoE event record, diagnostic log, firmware version, grounding measurement, or LED-code definition is supplied.
The affected systems include mostly trolleybuses and occasionally standard buses. Connected loads include Axis PoE cameras and Iris APC sensors associated with an Iris recorder. Because two switch models reproduce the symptom, shared vehicle power, wiring, grounding, connected devices, and load behavior remain investigation targets rather than confirmed causes.
Isolation Procedure
- Reproduce the startup event while recording the switch input voltage at its terminals. Capture the complete period before, during, and after the synchronous flashing; a delayed energization test does not prove that voltage remains stable after the delay expires.
- Repeat startup with all PoE endpoint cables disconnected. If the switch remains responsive, reconnect the Axis cameras and Iris-connected equipment incrementally until the symptom returns.
- If the failure persists with endpoint cables removed, test the switch from an independent power source while preserving the vehicle startup sequence. This separates the switch and network load from the vehicle supply path.
- Inspect and measure the shared supply return, grounding, connectors, protection devices, and cable terminations under startup conditions. Do not change grounding arrangements without reviewing the vehicle electrical design.
- Collect firmware versions and diagnostic records from each switch. Compare the observed LED rhythm with the manufacturer-defined indication before labeling it a boot loop or PoE trip.
Verification and Escalation Data
A corrective action is verified only when repeated vehicle startups complete without synchronous flashing, loss of switch response, or a required hard power cycle while all intended PoE devices are connected. Record which vehicle type, switch model, endpoint combination, and power arrangement were present for every test.
If escalation is required, provide the switch manufacturers with the startup voltage recording, wiring and grounding layout, connected-device inventory, firmware information, isolation results, and video of the LED sequence. The current evidence is insufficient to recommend a firmware adjustment or specific PoE setting.
FAQ
Why do all occupied TSW101 port LEDs flash together?
The evidence confirms synchronous repetitive flashing during an unresponsive state, but it does not establish whether the switch is rebooting or activating PoE protection. Correlate the pattern with input-voltage measurements and manufacturer diagnostics.
Will delaying TSW101 power after ignition stop the boot loop?
Not in the reported installation: delaying power by 15–30 seconds did not prevent the failure. Measure voltage during the entire startup event because instability may remain after the delay expires.
Does replacing the TSW101 confirm a defective switch?
No. A Rosho 8s reproduced the same flashing and freeze, which directs troubleshooting toward shared power, wiring, grounding, or connected loads without proving any one of them is the cause.