Antminer S19 – Temp Sensor Failure

Power-cycle the miner at the breaker for 60 seconds — not a soft reset, not a UI reboot, a full AC-off cycle. This drains the PIC's supply capacitors fully and clears any latched state from a transient I²C fault or cold-boot race. On cold days (sub-5 °C ambient), wait 5 minutes after first power-on before declaring the fault. Observe for 5 full minutes after power returns. If temp_pcb / temp_chip return to normal and stay there, you're done — re-baseline in 24 hours.

Update to the latest stock Bitmain firmware from support.bitmain.com/downloads for your specific hardware revision. Verify the build board code on the hashboard sticker before flashing — wrong firmware for a late-rev board will brick the control board. If you're already on latest, try rolling one version back; certain pre-2022-06 S19j Pro builds had a known BMminer regression that latched the sensor-failed flag even with healthy hardware.

Physically inspect intake/exhaust airflow and dust loading. Shop-vac both fan grilles, wipe the intake face, verify at least 15 cm of clearance front and back. A heavily-dusted heatsink can bake the PCB sensor area enough to push a marginal IC into reporting absurd values. Many intermittent-sensor-failure tickets turn out to be perfectly-working sensors reporting bogus numbers because the nearby PCB region is genuinely overheating.

Breaker off. Disconnect the PIC-to-control-board ribbon cable on the suspect chain. Inspect both headers under strong light — look for green/white oxidation, darkened contacts, bent pins, or cracked plastic. Apply a short burst of DeoxIT D5 or equivalent no-residue contact cleaner to the header pins. Let it flash off for 30 seconds. Reconnect firmly and listen for the retention-clip click. Humidity-driven oxidation is the #1 recoverable cause and clears a solid majority of first-time reports.

With the board out of the chassis, re-seat every connector: power terminals, chain-to-chain data cable, PIC programming header. Inspect for physical damage, melted plastic, or solder cracks around any large connector. Gently flex the ribbon cable end-to-end — if you hear or feel a crunch, the copper inside has fractured; replace the ribbon rather than debug it.

Swap the suspect hashboard into a different chassis slot. Label the 3 slots 0/1/2 with tape first. Boot and observe. If the sensor failure moves with the board, the fault is on the hashboard (sensor IC, PIC, or local I²C). If the failure stays in the same slot regardless of which board you install, the control board's ribbon connector or UART channel for that slot is the fault — Tier 4 control-board repair territory.

Multimeter in continuity mode, breaker off. Check continuity end-to-end on every conductor of the PIC-to-control-board ribbon cable. Any open circuit means the cable is dead — replace it. Ribbon cables for S19-family miners are CAD $15-30 from most ASIC parts suppliers; carry a spare in your bench kit.

Flash DCENT_OS — D-Central's open-source Antminer firmware. It exposes raw I²C bus traces, a live pic_status register, and per-chip temperature sensors independent of the PCB sensor IC. Alternatives: Braiins OS+, LuxOS, Vnish. Let the miner stabilize for 20 minutes, then pull the I²C trace log. A clean per-chip temperature read alongside a still-failed temp_pcb isolates the fault to the PCB sensor IC specifically — the easiest Tier-3 fix.

Probe the I²C bus at the PIC's SDA / SCL test pads with a multimeter (or scope, if you have one). At rest with the board powered, both lines should read 3.3 V DC from the pull-up resistors. 0 V on either line means the bus is shorted to ground or the sensor IC has failed short. Floating on either line means the pull-up resistor is dead. Replace the pull-up (typically 4.7 kΩ or 10 kΩ 0603 SMD — measure the silkscreen value before ordering). CAD $0.05 part; ~30 minutes of work.

Replace the PCB sensor IC. Desolder with hot-air at ~310 °C, clean pads with flux and braid, place a new IC with the correct footprint and part number. Bitmain has shipped at least three different sensor IC revisions on S19-family boards — verify the part number on your specific board's silkscreen before ordering. Reflash the PIC with stock PIC firmware after IC swap to ensure the I²C address table matches.

If both temp_pcb and temp_chip are dead on the same chain, suspect the PIC itself. Reflash the PIC using a PICkit 4 or equivalent programmer with Bitmain's official PIC binary for your hashboard revision. If reflashing fails or the PIC does not ACK on the programming header, the PIC is physically dead — replace it. This is small-pitch TQFP work and edges into Tier-4 territory if you are not experienced with it.

Inspect the 3.3 V rail feeding the PIC and sensor IC. Measure under load, not at idle. Sag below 3.15 V means a failing local regulator or a blown decoupling cap. Replace the regulator or bulk decoupling cap as indicated. This happens on boards that endured a PSU-side fault or lightning-adjacent event and is sometimes the real root cause behind a 'dead sensor' call.

Stop DIY when any of these are true: both temp_pcb and temp_chip are dead with the PIC not ACKing on its programming header; the I²C bus probes show hard shorts or missing pull-ups that you've already replaced without improvement; the ribbon connector on the control board itself is mechanically damaged; or you see burn marks, component discoloration, or a burnt-electronics smell anywhere on the board. Ship to D-Central — a test fixture with programmable load and scope-level I²C capture saves you more than further DIY at this point.

D-Central bench process for ERR_TEMP_SENSOR: full board inspection under microscope, I²C bus capture with a dedicated analyzer, sensor IC and PIC replacement with verified-genuine parts (we cross-reference part numbers against Bitmain's hardware table to avoid counterfeit sensor ICs, a real problem on aftermarket parts), 3.3 V rail integrity check, post-repair 24-hour burn-in at nameplate with live temperature logging.

Ship safely: hashboards in anti-static bags, double-boxed with at least 5 cm of foam on every side. Include a note listing the exact failure sentinel value (0 °C, -40 °C, -127 °C, 255 °C, blank), your firmware version, and your observed symptoms — that intel saves us diagnostic time, which saves you money. Canadian customers get domestic shipping rates; US and international shipments welcomed with clear customs documentation included.