Avalon 1346 – Fan Speed Error

Hard power cycle at the breaker. Flip the breaker feeding the 1346 (the IEC C19 draws up to 16 A; nameplate ~3300 W means a dedicated 240 V circuit). Wait a full 60 seconds for 12 V rails to discharge. Bring it back. Watch the UI during the first 3 minutes post-boot. Phantom `FAN_FAULT` events from AUC3 I²C timing glitches often clear on a cold start and don't return until the next ambient spike. If this clears the fault, log the ambient temperature at failure — you have a marginal thermal environment, not a hardware failure, and the real fix is better airflow or a lower performance bin.

Visual inspection of all four positions. Unscrew the chassis top (four Phillips screws — stock 1346 uses M3 with blue thread-lock; replace them if you strip one). Shine a phone flashlight across both rotors of each `HA1250H12SB-Z`. Look for dust buildup on blades and around the hub magnet, objects wedged between the rotors (a zip-tie, a missing washer, a dropped nut from a prior service), discolouration indicating heat-kill on a bearing. Dust on the top rotor is the signature 1346 failure mode — the top rotor is upstream in the counter-rotation pair and eats the intake dust load first.

Clean intake and blow out all four assemblies. Shop-vac the intake grille (front of the 1346 chassis). Then hit each fan with dry compressed air (canned or a dry shop compressor — never wet / unfiltered shop air). Hold each rotor with a chopstick or plastic pick so it does not over-spin — over-spinning a dead-powered fan damages the bearing worse than the dust it's being cleared of. Wipe visible hub surfaces with 99% IPA on a lint-free wipe. Roughly 30% of what Canadian customers ship D-Central as "dead 1346 fan" tickets are actually "heavily contaminated 1346 fan" tickets that clear at this step.

Check ambient and airflow clearance. Canaan's A1346 / A1366 manual gives temperature bands of 45 – 55 °C and 55 – 60 °C for different performance modes — those are chip / PCB measurements, not ambient. Keep inlet ambient ≤ 35 °C. Nothing within 15 cm of the intake. If the 1346 is in a closet or a small room and the exhaust recirculates, the MM enters a thermal protection state that reads almost identical to a fan-speed fault on the dashboard. Move it, duct the exhaust out of the living space, or ventilate the room. For Canadian operators running the 1346 as a space heater (3300 W is genuinely useful for a 300-400 sq ft insulated garage in winter), this is where you ductively balance "heat output where you want it" vs "intake air temperature the miner can tolerate."

Re-seat all four fan harnesses. Power off. For each `HA1250H12SB-Z`, unplug the 4-pin at the MM header and at the fan extension cable (the 1346 uses 4-pin fan extension cables per the manual). Inspect pins. Plug back in firmly. Dielectric grease on re-seat. Vibration from 24/7 operation works these connectors loose after 6 – 18 months — in the field this single step catches a surprising share of persistent `FAN_FAULT` tickets, especially on units that spent a winter shipping between operators.

Measure PSU3400 rail under load. Multimeter on DC. Probe the 12 V rail at the hashboard input while the 1346 is fully hashing (or the closest-to-full-hash state you can get it to before the fault triggers). Expect sustained 12.0 – 12.3 V. Anything under 11.6 V sustained means the PSU3400 is sagging — fan tach signals ride on rail stability, and a tired PSU produces erratic RPM reads that mimic a dying fan. Swap PSU with a known-good PSU3400 to isolate. On the 1346, the PSU3400 ships as an all-in-one with an IEC C19 input; confirm your input voltage is 200 – 300 V AC (dedicated 240 V circuit strongly preferred — 208 V stacks are marginal, 120 V single-phase is out of spec).

Swap the suspect `HA1250H12SB-Z` with a known-good unit. Spec: 12 V, 9 A rated, 120 × 120 × 50 mm, dual-rotor counter-rotating, 4-pin PWM, high static pressure, rated for a 1346/1366/1466/1566 chassis. Zeus Mining stocks the original part at ~$8 USD (minimum order 10, 150-day warranty). Generic single-rotor 120 × 38 PC fans will not work on the 1346 — insufficient static pressure through three hashboards worth of A3200CFA pin-fin heatsinks means you will chase cascading thermal faults for weeks before you capitulate. Secure all four Phillips screws on install; a missing screw causes vibration harmonics that walk the others loose over months.

Test each `HA1250H12SB-Z` across all four MM headers. Power off. Move one known-good fan through headers 1 → 2 → 3 → 4, powering on briefly at each to read RPM. If a specific header never reads RPM regardless of which fan is plugged in, the MM tach circuit for that channel is dead (Tier 3 or Tier 4). If a specific fan never reads RPM regardless of header, the assembly is dead (swap). This isolation takes 10 – 15 minutes and eliminates the biggest "is it the board or the fan" ambiguity faster than any other single test.

Verify PSU3400 fan with a `PS[0]` query. Use the `ascset` / `ps` command sequence over port 4028 to pull the PSU status bitmap. Decode bit 11 (`2048` decimal = `0x800`). If set, the failure is inside the sealed PSU3400, not the chassis. Record the `PS[0]` value and the ambient temp at fault — useful context if you ship the PSU3400 to D-Central for service. On the 1346 the PSU3400 fan is accessed only by opening a sealed housing. Do not do this unless you have live-rail experience with 200 – 300 V AC bulk caps.

Clean the AUC3 contacts and re-seat. Power off. Unplug the AUC3 from its USB host and from the MM's 2×5 IDC ribbon. Clean both contact rows with 99% IPA on a dental pick (gentle — the plating on AUC3 IDC pins is thin). Re-seat firmly. A tired AUC3 header produces I²C bus errors that surface as phantom `FAN_FAULT` events, especially under high ambient where bus capacitance shifts. Free, 5-minute check.

Flash a known-good Canaan MM firmware. Download signed 1346-family images from `avalonminer.org/firmware-document/`. Flash via the AUC3 utility with the miner in an idle state. Observe 30 minutes for phantom faults. If the fault clears on a one-version-back build, log the buggy version string for the community. Note: `DCENT_OS` — D-Central's open-source Antminer firmware — does not run on the 1346. Wrong silicon family. `DCENT_OS` support for Canaan hardware is on the D-Central roadmap but not shipping today; for now, the Canaan signed image is the only MM path. Do not trust unsigned third-party 1346 MM builds unless you are the one who compiled them.

Tune the AUC3 I²C bus timing. If phantom `FAN_FAULT` events persist at high ambient on a firmware rollback, the AUC3 is sampling the tach on the wrong PWM edge. In cgminer, set `--avalon7-aucspeed 400000 --avalon7-aucxdelay 24` (defaults `400000` / `40`). Lower `aucxdelay` tightens the sampling window. Undocumented in Canaan's public material, covered in the ckolivas cgminer `ASIC-README` for the Avalon7/8/10/13 family (the 1346 is in this `avalon7-*` command tree).

Replace the MM fan header MOSFET or tach pull-up. If Step 8 identified a dead header, the PWM-side MOSFET or the tach-line pull-up resistor is usually the culprit. Use a 3× loupe or a USB microscope to locate the failed part (discolouration, cracked package, blackening at the pad). Desolder with hot air at 300 – 320 °C, replace with the same package / same spec, verify continuity with a multimeter before re-powering. Expect 30 – 60 minutes of bench work per header and SMD rework experience on QFN / small SOT packages.

ASIC chip-level awareness (context, not a fan fix). If the `FAN_FAULT` has been running long enough to cook the hashboard, the downstream failure is usually a specific A3200CFA chip in the middle of the longest heat plume — typically mid-board, mid-chain. The Zeus A3200CFA replacement tutorial covers the chip swap; the BIN number on the replacement chip must match the BIN silkscreen on the hashboard or you'll see `MW` / `ECHU` cascade faults on boot. This is a bench-level job. We mention it here so you know what you're buying if you run the miner past the fault.

Inspect MM rail regulators. A damaged 12 V → 5 V or 12 V → 3.3 V buck on the MM makes the tach-reading MCU interpret rail noise as RPM fluctuations. Measure at test points. Any rail more than ±5% off nominal (5 V rail: 4.75 – 5.25 V; 3.3 V rail: 3.13 – 3.47 V) means the MM needs component-level repair or replacement. Outside those windows, stop and ship — you're chasing a rail problem, not a fan problem.

Know when to stop. Ship the 1346 to D-Central when any of the following is true: `PS[0] = 2048` PSU3400 fan failure and you do not have live-rail PSU experience; more than one MM fan header dead simultaneously; replacement `HA1250H12SB-Z` reports the same fault on the same header; visible MM damage (burnt components, bulging caps, scorched traces); bricked AUC3 or MM after a flash attempt; cascade faults combining `FAN_FAULT` with `ECHU` and rising `PVT_T`. [Book an Avalon repair slot →](https://d-central.tech/services/asic-repair/). Canada-wide, US and international welcomed.

What D-Central does at the bench. Test fixture with programmable 200 – 300 V AC input and per-channel fan-harness isolation for sustained fault reproduction. Logic-analyzer capture of the AUC3 I²C bus for timing bugs. Component-level MM repair (tach MCU, I²C controller, rail regulators, PWM MOSFETs). PSU3400 recap / full replacement on sealed units. Hashboard component-level repair if the fault has been allowed to run long enough to take out A3200CFA chips (BIN-matched replacement — this is where the Zeus-documented chip swap procedure becomes a repair line item, not a guide). Post-repair 24-hour burn-in at nameplate hashrate before return ship, with `Fan[]`, `PVT_T`, and `GHSavg` logs attached to the ticket.

Ship safely. Pull the PSU3400 out of the chassis. Pack separately. Pull the three hashboards into anti-static bags. Wrap the chassis in 5 cm of foam on every face. Double-box. Include a plain-text note: observed symptom, intermittent vs. constant, current MM firmware version, `PS[0]` value if captured, ambient temperature at fault, contact info, and what you already tried. Every piece of context cuts bench diagnostic time — and diagnostic time is what the repair bill buys. The 1346 is a new-enough model that customer-shipped context is often the difference between a 5-day and a 10-day turnaround.