Bitaxe – Reverse Polarity Barrel Jack Damage

Unplug the wrong PSU at the wall, not at the board. Some bench PSUs and cheap adapters keep output live for 2-5 seconds after AC is cut. Pull the plug from the outlet, then disconnect the barrel jack from the Bitaxe. Every extra millisecond of reversed polarity propagates more damage. This is a time-sensitive first move — do not pause to take a photo first.

Do not plug a known-good 5V PSU in to test. A board with a fried D2 or shorted TPS546 will trip a healthy 5V brick (best case) or push current into damaged silicon and cascade the failure (worst case). Wait until cold-resistance checks in Step 6 confirm the rails are healthy before applying any further power. Five minutes of multimeter work prevents hours of follow-on troubleshooting.

Photograph the offending PSU label and the board before you touch anything. Phone camera, macro mode if available. Capture the brick's polarity diagram (the centre-negative symbol is your evidence), voltage, current rating, and any brand markings. Photograph the board: visible damage on D2, the TPS546, the ESP32 module, the barrel jack area. This documents the incident for D-Central diagnosis if you ship the board.

Mark the offending brick `DO NOT USE — REVERSE POLARITY` permanently. Sharpie on the case, or red electrical tape over the barrel connector. If the brick is unbranded or the polarity diagram is missing, throw it out. The single most common cause of reverse-polarity damage in repeat customers is the same brick coming back out of the drawer six months later because nobody marked it dead.

Visually inspect the board under magnification. Loupe or USB microscope. Focus on D2 (SOD-123 or SMA near the barrel jack), the TPS546 QFN, ceramic caps on the input side, the ESP32-S3 module's 3V3 LDO area, and the barrel jack solder joints. D2-only damage with everything else clean is the best-case scenario. TPS546 or ASIC damage moves you to Tier 3/4.

Run cold resistance checks with the board unpowered. Multimeter on diode/continuity. Probe GND to 5V input pad (healthy >10 kOhm rising); GND to VCORE output cap (healthy >1 kOhm); GND to ESP32-S3 3V3 pin (healthy >5 kOhm); direct diode test across D2 (healthy Schottky ~0.2-0.3V forward, OL reverse — `0 Ohm` both directions means D2 fused short). Record all four. These determine which tier of salvage is even possible.

Replace D2 if it is the only failure. If diagnostics show D2 shorted and every other rail healthy, this is a `$0.30 CAD` Schottky-diode swap. Source a 1A 40V Schottky in SOD-123 or SMA package matching your rev from Digi-Key or Mouser. Hot-air rework, no soldering iron on SOD-123 if you can avoid it. Pay attention to orientation — Schottky diodes are polarised, and installing it backwards reproduces the same fault path. Re-verify cold resistance after the swap before applying any power.

Current-limited bench power-up only after Steps 6/7 are clean. Bench PSU at 5.0V, current limit 100mA. Verify polarity at the probe before connecting — red to centre, black to barrel. Watch for the healthy boot current signature: brief spike to ~300mA (over limit, PSU folds back), then settle to 50-80mA idle as the ESP32 brings up WiFi. Step the limit up through 2A, then 6A, observing draw at each stage. Pinned current = something is shorted, power off.

Replace input-side ceramic caps if any look stressed. Reverse polarity stresses ceramics even when they do not visibly fail — invisible cracking or dielectric damage that progresses over weeks. Common values: `10 uF / 10 V X7R 0805` and `22 uF / 10 V X7R 0805`. Verify against the Bitaxe reference schematic on GitHub for your specific rev. Failure to replace stressed-but-not-obviously-dead caps leads to intermittent failures 30-90 days later, often presenting as random reboots that look like firmware bugs.

Run a 24-hour burn-in after any successful repair. Stock frequency (`485 MHz` Gamma, `490 MHz` Supra, `485 MHz` Ultra), log hashrate and temperature every 5 minutes for a full day. Stable across burn-in = real salvage; drift, intermittent zero-hashrate, or thermal anomalies = latent damage. Reverse-polarity boards that boot but fail burn-in are showing silicon damage that did not manifest at room temperature but does under sustained thermal load.

TPS546 replacement for a shorted VCORE rail. Source the TPS546D24A (Supra / Ultra older revs) or TPS546D24S (Gamma / GT / newer revs) from Digi-Key or Mouser — AxeOS `v2.7.x+` recognises both, older firmware only one. Fine-pitch QFN hot-air rework: preheat 150C bottom-side, top-side hot air 310-330C for ~30s, no-clean flux, tweezer alignment, no soldering iron. Honest expectation: if the TPS546 blew, the ASIC probably blew too — confirm before celebrating.

BM1366 / BM1368 / BM1370 ASIC replacement — the hard call. Even with fresh D2 and TPS546, if the ASIC saw reversed 5V on VCORE during the failure cascade, it is almost certainly dead. BM1366/BM1368 are scarce but available through grey-market channels; BM1370 is very hard to source even for D-Central. BGA rework: pre-heat plate, hot air, no-clean flux, re-balling, controlled reflow. Budget 3-4 hours and `$100+ CAD` in parts. At that point a fresh board with warranty often makes more economic sense than the rework.

Replace any input-side TVS diode that triggered. Some Bitaxe revs include a `SMBJ6.0A`-class TVS diode in addition to (or instead of) D2. If your rev has one and it reads open or shorted after the event, replace it. SMBJ6.0A from Digi-Key costs pennies. Hot-air rework. The TVS catches over-voltage events even when polarity is correct (lightning-adjacent surges, switching transients), so installing a fresh one is value-add even if it did not trigger this time.

Inspect PCB vias and traces near the barrel jack. Severe reverse-polarity events can pop vias as well as components, particularly on revs without a fast-acting D2. Strong light and a loupe. A burnt via or blown trace can be repaired with thin-gauge magnet wire bridge — ugly but functional. Damage to a main power plane, however, is usually the end of the board's economic life — a replacement board makes more sense than a multi-hour PCB salvage.

Clean the board thoroughly after rework. Flux residue plus damaged components plus newly installed parts is a recipe for intermittent failures. Isopropyl 99%, soft brush, compressed air. Do not use ultrasonic cleaning on a populated Bitaxe — the ESP32-S3 module is not ultrasonic-safe and the cleaning process can damage the module's RF shielding and crystal. Visual inspection under magnification is mandatory before re-powering.

Stop DIY and ship to D-Central when: BM1366/1368/1370 itself is visibly damaged, multiple rails measure as shorts, you have replaced D2 and TPS546 and the board still will not boot, the board boots but fails 24-hour burn-in, or you do not own a hot-air rework station and the damage is past D2-only replacement. Book a Bitaxe repair slot at https://d-central.tech/services/asic-repair/. We deliver honest salvage-vs-replace calls and do not invoice jobs that are not economical.

D-Central bench process for reverse-polarity incidents: full damage survey under microscope, quantified damage report inside 48 hours, salvage-vs-replace quote with transparent pricing, D2 / TVS / TPS546 / ASIC rework as needed using the same parts and processes our production line uses, 24-hour burn-in under sustained load, QC sheet documenting the repair. Turnaround typically 5-10 business days for salvageable boards. Canada / US / international shipping welcomed.

Ship safely. Anti-static bag, bubble wrap, rigid outer box with `>=5 cm` foam on every side. Include the offending PSU if you still have it (with the polarity-diagram label visible) — it confirms the incident vs other damage vectors and helps us catalogue recurring offending brands. One-page note: approximate exposure duration, symptoms observed (smoke, popping, smell), firmware version before the incident, whether the board has been powered on since, and contact info. Saves diagnostic time at the bench, saves you money on the invoice.