Antminer L3+ – Temperature Too High

Hard power-cycle the miner. Flip the PSU switch off for `60 seconds`, back on. Don't do a soft reboot from the UI — you want to clear the kernel state and let the PIC chips cold-boot. Watch boot logs: all four chains should go green within 2 minutes. If one chain doesn't come up clean after a full cold boot, note which one — that's your suspect board.

Verify intake air temp at the grille. Grab an IR thermometer or even an indoor-outdoor digital thermometer, place the probe `5 cm` off the intake grille. Target `≤ 30 °C`, hard ceiling `35 °C`. If your intake is above `30 °C`, open a window, redirect an auxiliary fan, move the miner out of a confined space — whatever it takes. An L3+ at `40 °C` intake will never pass temp, no matter how clean.

Blast dust out of the chassis. With the miner powered down, use a compressed-air can or shop compressor at `<60 psi`, direct short bursts through the intake grille and the heatsink fins. Hold the fan blades with a finger so they don't spin and back-feed current into the fan controller. Work outside or over a garbage bag — you will find years of pet hair and pocket lint.

Cover clearance audit. Walk around the miner. Is there anything within `15 cm` of the intake? Anything within `20 cm` of the exhaust? Curtains, towels, stacked boxes, a second miner's exhaust dumping into this one's intake? The L3+ is a `600 – 800 W` space heater that needs to breathe.

Roll firmware back to stock Bitmain L3+. If you or a previous owner flashed a third-party firmware (VNish, AsicBoost, "L3++ OC" packages), download the last official Bitmain image from `support.bitmain.com/downloads`, flash via the web UI → System → Upgrade. Stock first, diagnose second. Some overclock firmwares spike `BM1485` temps `10 – 15 °C` over nameplate and trip `ERR_TEMP_HIGH` on hardware that's otherwise healthy.

Replace the fan(s). The L3+ uses two `120 × 38 mm, 6000 RPM` axial fans (PWM 4-pin). Listen for bearing whine, watch for `0` RPM or sub-`5500 RPM` reports in the UI. Pull the fan, check the part number, order a matched replacement — Delta `FFB1212EH`, Sanyo Denki `9GA1212P4G001`, or equivalent. Budget `CAD $20 – $40` per fan. Don't mix sleeve and ball-bearing fans — different noise, different lifespan, they'll wear unevenly.

Inspect and reseat every ribbon and power connector. Power off at the breaker. Disconnect each hashboard's 2×4 power connector and ribbon cable. Check pins under a loupe for green oxidation, blackening, or bent contacts. Clean with `99%` isopropyl alcohol and a lint-free swab if you see corrosion. Reconnect firmly, listen for the click. A corroded ribbon gives the exact same log signature (`255` / `fail to read pic temp`) as a dead PIC chip — always rule out the cable first.

Swap hashboards between slots. Label the four slots `0/1/2/3` with masking tape. Move the suspected-bad board to a known-good slot. Boot, let it hash for 15 minutes. If the bad temp follows the board, the board is at fault (Tier 3 territory). If it stays in the slot, the chassis airflow in that slot is compromised (blocked fin section, stuck fan, or a cable inside the chassis interrupting airflow).

Test the PSU under load. L3+ PSUs (typically `APW3++` or `APW7`) tire out after years of continuous load. Measure DC output at the PSU-to-miner connectors while the miner is actively hashing. Target `~12 V` sustained. Below `11.5 V` under load = PSU is sagging, and the resulting higher current draw shows up as additional heat at the voltage-regulator domain, indirectly feeding `ERR_TEMP_HIGH`. Swap with a known-good PSU as a crossover test.

Verify ambient and intake air path during worst-case. If the problem is worse in summer, intermittent in mid-afternoon, or correlates with outside temp, the root cause is ambient. Log intake temp every hour for 48 hours with a cheap data-logger thermometer. If intake exceeds `32 °C` at any point, re-engineer the installation — duct the exhaust outdoors, add a room AC, move the miner to a cooler space.

Replace thermal paste on all four hashboards. This is the highest-impact L3+ repair by a wide margin. Disassemble each board: unscrew heatsinks, lift carefully (they stick when paste has cured), scrape old TIM off each of the 72 `BM1485` dies with a plastic scraper, clean with `99%` IPA + lint-free wipes. Apply a thin, uniform layer of Arctic MX-6 or Thermal Grizzly Kryonaut — pea-dot per chip, let the mount pressure spread it. Reassemble, torque evenly. Budget `CAD $25 – $40` in paste for all four boards. Expect `10 – 20 °C` temperature drop. This single fix saves more L3+s than everything else combined.

Inspect and replace crumbled thermal pads on the voltage domain ICs and the PCB-side heat-spreaders. The L3+ uses `1.5 mm` and `2.0 mm` pads on its buck converters and PMIC regions. When they harden and shrink (common by year 3+), the regulators run hot and the board reports hot even though the `BM1485`s are fine. Use Fujipoly Sarcon or Arctic TP-3 pads at matching thickness. Budget `CAD $15 – $25` per board.

Reflow a suspected dead `BM1485` or PIC16F1704. If Tier 2 / diagnostic Step 6 isolated a dead PIC (temps stuck at `255` with good cables) or a specific chip position reading wildly different temps, warm up a preheat station to `150 °C` on the board bottom, hot-air the target chip top-side at `300 – 320 °C` for `25 – 35 seconds`. Let cool naturally — don't quench. The `BM1485` is a TSMC 28 nm package from 2016 — tolerant of one reflow, sometimes two. A successful reflow restores BGA joints without chip replacement and costs you nothing but time.

Reflash the PIC firmware on a hashboard that still reports `255` after reflow and cable swap. The PIC can be reprogrammed with a PICkit 3 / PICkit 4 and Bitmain's `hash_board_code` binary (circulated in repair-community channels — check BitcoinTalk L3+ repair thread for verified copies). Bitmain doesn't document this procedure publicly; it's the difference between a `CAD $400` board replacement and a `CAD $15` reflash. Ground yourself, probe `ICSP` header on the hashboard, confirm voltage, flash, verify, reassemble.

Cross-flash firmware for per-chip diagnostics. The L3+ is old enough that most modern custom firmwares don't support it — `BM1485` isn't on the priority list for Braiins OS+ (SHA-256 focus) or LuxOS. For L3+, the realistic options are stock Bitmain latest or the last known stable community firmware build for Scrypt on L3+ hardware. Use whichever stock version gave you the cleanest logs historically. DCENT_OS — D-Central's own open-source Antminer firmware — currently targets the SHA-256 Antminer family (S17-class and newer); L3+ support would require a Scrypt-miner port. If you're the kind of operator who'd fund that port, email us.

Stop DIY if: you've reflowed a PIC or `BM1485` once and the fault returns within `30 days`; a specific chip position on *two different boards* reports wildly divergent temps (PCB-level problem, not chip-level); you see capacitor bulging, discoloration, or smell burnt electrolyte (`ALCAP` aging is real on 2017-class boards); or your multimeter shows a short on the voltage rail to a hashboard. [Book a D-Central ASIC Repair slot](https://d-central.tech/services/asic-repair/) — Canada's Mining Hackers have seen every failure mode of this miner.

What D-Central does at the bench. Test fixture with programmable load, per-chip isolation using Bitmain's `hash_board_code` tool, `BM1485` chip replacement from salvaged-grade stock, full thermal-pad and paste refresh, PIC reflash via PICkit 4, post-repair 24-hour burn-in at nameplate `504 MH/s` with temperature logging. If the board can be saved, it's saved. If it can't, we'll tell you honestly and offer a salvaged-grade replacement board.

Ship safely. Anti-static bag each hashboard individually. Double-box with `≥ 5 cm` of foam on every side. Include a note: observed symptoms, firmware version, kernel-log excerpt, your contact info. Canada Post or UPS works fine within Canada. Saves us diagnostic time — saves you repair dollars.