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Status LED

Hardware version

CANBench Duo v1.1 — Fabricated prototype, sole built unit. V1.1 is electrically identical to the V1.2 schematic refresh but predates the InvenTree symbol-library migration; the schematic component metadata reflects legacy SCADYS naming. Testing and bench validation reference this V1.1 hardware.

Other versions: v1.2 — schematic refresh (next version)

A single RGB LED on the top extrusion communicates the supply-chain health of the CANBench Duo. There is no MCU, no firmware, no software — each colour falls out of the rail relationships in the protection chain, so what you see is the true state of the hardware at that instant.

State table​

IndicatorConditionWhat to do
OffNo bench-supply voltage at the SRC banana pairCheck the bench supply is on and wired to the SRC banana pair (front faceplate, RED to SRC+, BLACK to SRC−).
GreenCorrect polarity, normal operationProceed with measurement. LISN delivers the filtered supply to the DUT bananas (J1 / J3) and the M12 N2K connector (J10).
BlueQ2 protection FET not fully conducting — typically because F1 has blownPower the bench supply down. Remove the DUT. Replace F1 (Littelfuse Nano2 Slo-Blo 5 A, in the 154 series holder). If Blue persists with no DUT attached and a fresh fuse, suspect Q2. Investigate the DUT for an over-current condition before reconnecting.
RedReverse polarity at the SRC pair (V_BLACK > V_RED)Power the bench supply down. Reverse the SRC cables to the correct RED-to-SUPPLY+, BLACK-to-SUPPLY− orientation.

Brief Blue flash at power-on is benign​

A brief Blue flash for a few ms at supply turn-on is normal. Q2's gate-bias divider takes a few RC time constants to bring Q2 fully ON, and during that interval the V(SUPPLY+) − V(VSS+) gap momentarily exceeds the LED state-encoder's threshold. The LED settles to Green once Q2 reaches full conduction.

If the Blue persists (does not settle to Green within ~ 100 ms), treat it as a fault per the state table above.

Troubleshooting flow​

  1. LED is Off but the bench supply is on and the wiring looks right.

    • Check the SRC banana sockets for a loose or oxidised contact.
    • Verify the bench supply is actually delivering voltage at its output terminals (use a multimeter at the SRC banana pair).
    • If voltage is present at SRC and the LED is still off, the LED's own bias circuit may have failed — escalate to engineering.

  2. LED stays Red after reversing the cables.

    • Confirm the cable polarity at both ends — sometimes only the bench-supply end gets swapped while the banana end stays reversed.
    • Multimeter at the SRC banana pair: SRC+ should read positive relative to SRC−.

  3. LED stays Blue after replacing the fuse and removing the DUT.

    • The fuse has likely blown again under no load, or Q2 is faulty.
    • With the bench supply OFF, check F1 for continuity (multimeter, fuse out of holder).
    • If F1 is intact, Q2 is the next suspect — escalate to engineering.

  4. LED is Green but the DUT shows no supply at its connector.

    • The LED reports the protection-chain state, not the DUT-side voltage. Measure VDUT directly at the DUT banana pair (J1 / J3).
    • If VDUT is absent despite Green, suspect a wiring fault between the DUT banana pair and the DUT, or an open in the LISN filter ladder (rare — would also affect the noise floor).

Engineering rationale​

For the circuit topology, component values, and the reasoning behind the four-state encoding, see Power Indicator LED in the Circuit Design section. The state table on this page is the operator-facing summary; the circuit-design page is the engineering source of truth.

For a fast lookup of the state table without context, see Quick Reference → LED States.