Bitaxe Gamma Barrel Jack Undervolt Boot Loop

Move the Gamma directly onto a wall outlet on its own circuit. Unplug from every USB hub, surge strip, smart strip, extension cord, and shared adapter. Don't share the circuit with a fridge compressor, microwave, HVAC blower, or washing machine. Shared-rail brownouts disappear on isolation — do this before changing anything else, it's free and takes 30 seconds. Observe 10 minutes of boot stability via OLED or serial before assuming this didn't help.

Swap the PSU for a known-good Bitaxe-rated 5V 6A (or larger) barrel supply. D-Central stocks supplies sized correctly for Gamma at stock and overclocked tunes. Don't grab the closest spare; use a fresh, named-brand brick (Mean Well GST series, Inventus, or D-Central-stocked equivalent) with verified ripple under 50 mV. Don't reuse the original PSU 'to test' — its label is aspirational, that's why you're here. If the loop clears, replace permanently and don't move the failed PSU to another miner — it's also undersized for that one.

Swap the barrel-jack cable for a short, thick-gauge cable. Maximum 1 metre, minimum 20 AWG (lower AWG = thicker wire). Match the connector to the Gamma jack: 5.5x2.1 mm or 5.5x2.5 mm depending on board revision (check the board sticker or compare physically). Verify the cable's marked gauge — unmarked cables are usually 26 AWG and will undo any PSU's regulation under Gamma load. A 1.5 m 26 AWG cable drops 0.30 V at 5 A — turning a clean 5.05 V supply into 4.75 V at the jack. Mark the working cable; throw out the unmarked thin ones.

Inspect the barrel jack and connectors with a loupe or magnifier. Center pin straight and not spread. Solder around the jack footprint clean and unbroken (no hairline cracks). No discoloration on the contacts. No dust or lint in the connector. Wipe contact surfaces with 99% IPA on a lint-free wipe; let dry 60 seconds before re-mating. Connector resistance under high transient ASIC current drops enough voltage to trigger the BOD exactly like an undersized PSU does.

Confirm the reset reason on serial console. Plug USB-C from Gamma to laptop. Open serial monitor at 115200 8N1: `idf.py monitor`, `pio device monitor`, Arduino Serial Monitor, `screen /dev/ttyUSB0 115200`, or PuTTY on Windows. Power the Gamma from its barrel jack — not from laptop USB. You want real ASIC load behaviour, not USB-bus-limited idle. Capture three full boot cycles. You should see `Brownout detector was triggered` and / or `rst:0xf (RTCWDT_BROWN_OUT_RESET)`. Different reset reason means you're on the wrong page — see Related Errors before continuing.

Measure VIN at the barrel-jack solder pads under load. Multimeter on DC volts. Probe at the board, not the cable end or PSU end. Power the miner and read voltage during idle, during ASIC ramp transient (1-3 seconds after OLED splash where BM1370 starts pulling current), and during the brownout itself. Target: >= 4.9 V sustained, never below 4.7 V on transient. If VIN reads below threshold under load despite a known-good PSU and short thick cable, you're dealing with a downstream-pull problem (likely TPS546 cascade or shorted cap) — Tier 3.

Measure 3V3 at any accessible ESP32-side test point (most Gamma boards have a labelled 3V3 pad). Target: 3.27-3.33 V sustained under load. Clean VIN combined with collapsing or oscillating 3V3 means the 3V3 buck on the ESP32 side has failed — that's hot-air rework territory, not a soldering-iron job. If 3V3 is clean but BOD still trips, the transient is below multimeter bandwidth — go to Step 8 with a scope.

Run a DC electronic-load test on the suspect PSU at 1.5x Gamma nominal. Atorch DL24 or equivalent. A 5V 6A PSU should hold >= 4.95 V at 4 A continuous with ripple <= 50 mV. Anything that droops more than 2% nameplate or rings with > 100 mV ripple is too soft for mining regardless of label. This catches the silent-killer aged PSU that passes idle multimeter checks but fails under real ASIC load. If the supply fails this test, replace it; don't move it to another miner.

Verify wall-outlet voltage with a plug-in voltage logger for 24 hours (Kill-A-Watt, Amprobe LM-100, or similar). If your wall voltage drops below 115 V (120 V nominal) during evening hours, your residential circuit is sagging during neighbourhood peak load and that drop is being faithfully passed through the PSU regulation onto Gamma's VIN. Fix at the wall, not the miner: dedicated circuit, line-interactive UPS, or relocate the rig. Common culprits: 5-10 PM neighbourhood peak, electric-heating mornings in winter, well pumps on rural circuits.

Tune AxeOS down to stock (or below) if the loop only started after pushing coreVoltage or frequency. From the AxeOS web UI under Settings -> System, set coreVoltage to default (typically 1.20 V on Gamma stock) and frequency to default (typically 525 MHz). Save and reboot. If it now boots cleanly on the marginal PSU, the supply was already at the edge — replace the PSU before trying to push the tune back up. Order matters: PSU upgrade first, performance experiments second. Pushing tune on a marginal PSU cascade-damages the TPS546 over time.

Scope VIN and 3V3 for sub-multimeter transients. Two-channel oscilloscope, 10x probes, >= 20 MHz bandwidth. CH1 on VIN DC-coupled at the barrel-jack pads. CH2 on 3V3 DC-coupled. Trigger on negative slope crossing 4.7 V on CH1. Capture the ASIC ramp. Look for: (a) transient sag (VIN momentarily dropping to 4.5 V or lower for tens of microseconds while average reads 4.95 V), and (b) input ripple (VIN swinging +/-200 mV or more at 50-200 kHz, indicating PSU ripple beyond TPS546 input filtering tolerance). Both kill regardless of nameplate.

Add bulk capacitance at VIN as a bench workaround for transient sag (NOT a permanent fix). Solder a low-ESR 100-220 uF electrolytic plus a 10 uF MLCC across VIN to ground at the barrel-jack solder pads. This absorbs ASIC-ramp transients that would otherwise sag the rail. If the cap solves the brownout, your supply path is at the edge — still upgrade the PSU or cable. Don't ship a Gamma to a customer with extra caps soldered on; this is a diagnostic confirmation tool, not a repair.

Re-solder the barrel-jack footprint if physical stress has cracked solder under the connector. Symptoms: cable wiggle correlates with brownouts; VIN reads clean directly at PSU end but drops at the jack. Remove old solder with wick, clean with 99% IPA, apply fresh flux, re-solder all four mechanical tabs plus the two power terminals with 60/40 or lead-free. Soldering iron at 360 C with a T12 tip; not a hot-air job. Verify with continuity test and a pull test before powering. Reseat the cable.

Replace the barrel-jack outright if the center pin is spread, corroded, or mechanically damaged. Hot air at 300 C for 30 seconds, tweezers, lift the jack. Clean footprint with wick and IPA. Install fresh 5.5x2.1 mm or 5.5x2.5 mm jack matching original (verify against board sticker). Re-solder all tabs and power terminals. Verify polarity before powering — reversed barrel-jack on Gamma instantly damages the TPS546 and the BM1370. A 5-dollar part fixes a chronic supply-path source on well-used Gammas.

Stop DIY and ship to D-Central ASIC + Bitaxe Repair when: three known-good Bitaxe-rated PSUs on three different outlets all reproduce the loop; VIN reads below 4.7 V under load on a 5V 8A supply with a short 18 AWG cable; scope shows clean rails but BOD still trips; serial shows both `Brownout detector was triggered` and `TPS546 Power Fault Detected` in the same cycle (cascade damage); visible damage on the buck converter, MLCCs, or barrel-jack footprint; or you don't own the bench gear to continue. Book at https://d-central.tech/services/asic-repair/. We stock TPS546 spares, ESP32-S3-WROOM modules, barrel-jack connectors, and every Gamma board revision. 3-7 business-day turnaround. Canada / US / international. D-Central pioneered the Bitaxe ecosystem — Mesh Stand, first heatsinks, every variant in stock.