Bitaxe – Fan RPM Reads Zero Despite Spinning (Tach Fault)

Open AxeOS in your browser. Navigate to Settings → Fan Control. Note the current PWM percentage. If it is under 25%, this alone may explain 0 RPM — the fan is below its tach-reporting threshold per Intel 4-Wire PWM Fan Spec. Bump it to 50% manually and watch the RPM field for 30 seconds.

Switch fan mode from Auto to Manual at 100% PWM. Save. Wait 30 seconds. If RPM jumps to a real number (3,000–8,000+ depending on fan), your fan tach is healthy at high PWM and goes silent at low duty cycle. Set a permanent PWM floor of 25–30% as your normal operating setting — this is a settings change, not a hardware fix.

Hard power-cycle the Bitaxe: pull power for 30 seconds, plug back in, wait for AxeOS to boot, watch RPM. Power-cycle clears stale-register state in the EMC2101, especially relevant on Gamma 601/602 with firmware in the v2.8.x range per ESP-Miner issue #1291.

Update AxeOS to current stable: Settings → System → Firmware Update. Read the changelog for any EMC2101 / fan-control fixes. If you are more than two minor versions behind, update first; many tach-reading bugs have been fixed across v2.7.x → v2.9.x. Power-cycle after the update completes.

Document the fan you have installed: photograph the fan label (manufacturer + model number). You will need this for replacement decisions in Tier 2 and for any community / D-Central support thread.

Power off. Pull the fan and count wires at the connector. Four wires = 4-pin PWM (continue troubleshooting). Three wires = 3-pin DC fan (this is your problem — replace with a 4-pin PWM unit). Two wires = power-only fan, no tach, no PWM (also replace). Bitaxe headers expect 4-pin PWM following the Intel spec.

Replace the fan with a verified 4-pin PWM unit. Recommended models in order of preference: Noctua NF-A4x20 PWM (40 mm, premium, ultra-quiet), Sunon MagLev MF40101V2-1000U-A99 (40 mm industrial), or D-Central's Bitaxe-tested replacement. Match fan size to your variant: Supra/Ultra/Gamma/GT use 40 mm; Bitaxe Hex uses 60 mm or 70 mm depending on heatsink config.

Verify wire ordering before plugging in. Industry-standard 4-pin PC-fan pinout (locking tab up): pin 1 = GND (black), pin 2 = +12 V (yellow), pin 3 = tach (green), pin 4 = PWM (blue). Bitaxe headers follow this standard. If the fan uses non-standard colours, trace by datasheet, not by wire colour.

Re-test with the new fan. Power up. Default Auto fan curve should ramp the fan from off to ~30% within seconds of boot. Watch RPM. Healthy 4-pin fan reads 2,000–8,000 RPM at idle PWM and scales to 8,000–14,000 RPM at 100% (varies by fan model). Correct readings = done. Still 0 RPM = Bitaxe-side problem, continue to Tier 3.

Power off. Unplug the fan from the Bitaxe header. Visually inspect for bent header pins, pushed-back contacts in the connector housing, oxidation, or debris. Reseat firmly. Apply a tiny amount of dielectric grease on the contacts if you live in a humid environment or have observed intermittent behavior. Reseat firmly. Power on and re-test.

Repair the cable if you have isolated the tach line as the broken conductor and the fan is otherwise good. Cut the connector, strip the sleeving, locate the broken tach wire, splice with fresh wire and heat-shrink, re-crimp a new 4-pin connector. Fast 20-minute job with the right crimp tool. If you do not own a crimper, replace the entire fan instead.

Scope the EMC2101 TACH pin while the fan is spinning at 100% PWM. Reference the Bitaxe schematic on github.com/skot/bitaxe to find the EMC2101 footprint (10-pin DFN package adjacent to the ASIC) and identify the TACH input. Expected: clean ~3.3 V square wave; frequency = (RPM/60) × 2 for a 2-pulses-per-revolution fan. At 6,000 RPM that's 200 Hz. Clean signal present = register / firmware issue. Floating / no signal = trace or component fault.

Continuity test from fan header tach pin to the EMC2101 TACH input. Open trace = bad PCB or cracked via — repair with bodge wire if you can find both endpoints, otherwise the board is scrap or ship to D-Central. Verify the pull-up resistor on the tach line (typically 10 kΩ to 3.3 V or 5 V — refer to schematic). Open or wrong-value pull-up = the symptom; replace the resistor.

Reflow the EMC2101 if the IC is suspect. Hot-air rework station at 290–310 °C for ~30 seconds with flux first; let the chip cool naturally without disturbing it. Don't poke or move the chip during cool-down. EMC2101 chips don't fail spontaneously, but a cold solder joint at a corner pin can produce exactly this symptom.

Roll AxeOS firmware back to a known-good version (e.g. 2.7.0), power-cycle, observe. Then flash current. This brackets the issue between firmware versions if it is software-side and gives you data to file an issue on bitaxeorg/ESP-Miner with your fan model, board revision, and the firmware diff.

Stop DIY when: a known-good 4-pin PWM fan also reads 0 RPM, continuity from header to EMC2101 fails, or you have reflowed the chip without resolution. PCB-level rework on a 4-layer Bitaxe board with fine-pitch components requires bench equipment most home miners don't own. Ship to D-Central — we built the original Bitaxe Mesh Stand and have repaired Bitaxes since the original v1 PCB.

What D-Central does at the bench: full I2C bus probe with EMC2101 register dump, scope on every relevant signal, optical inspection under microscope for cracked vias and solder bridges, IC replacement if the EMC2101 is dead (rare), firmware re-flash with a known-good AxeOS build, post-repair burn-in on a calibrated thermal load.

Ship safely: anti-static bag, bubble wrap, double-box. Include a note with your AxeOS version, the fan model installed, when the issue started, and what you have already tried. This saves D-Central diagnostic time and saves you repair cost. Book a slot via d-central.tech/services/asic-repair/.