Test Fixture

Test fixture is the repair-bench rig that lets a technician power and scan a single hashboard outside the miner so faults can be located precisely. The board connects to the fixture, which supplies controlled power and signalling, then runs a chip-by-chip scan reporting which ASICs respond, which are dead, and which underperform — along with the position of each fault on the board. This turns a vague "chain only finds X chips" symptom from the kernel log into an exact location to inspect and rework, which is why a fixture is the first major purchase of any serious repair bench.

What it measures

Beyond a pass/fail per chip, fixtures expose the test points used in diagnosis: the signals that pass through the chip daisy chain — CLK, CO, RI, BO, and RST — plus domain voltages such as VDD0V8 and VDD1V2. Chips on an Antminer board are wired in series for signalling, so watching where a signal stops propagating identifies the first failing chip in the chain; reading an abnormal domain voltage identifies a faulty voltage domain or its DC-DC circuitry. The operator moves from symptom to suspect component in minutes rather than probing blind. Diagnostic output typically arrives over a USB-to-TTL serial link to a PC, where the scan log names each failure by chip position.

The PT1/PT2/PT3 test sequence

Bitmain's own factory and repair flow formalizes bench testing into three stages, and good fixtures reproduce it. PT1 is chip enumeration: the fixture sends the initialization sequence over UART, addresses every chip, and compares the count against the expected total — a healthy S21 board reports 108/108, with failures shown as "ASIC NG: X". PT2 is a pattern test: known test vectors are sent to each chip and the returned nonces are checked, flagging chips that compute wrong answers even though they enumerate. PT3 is a frequency sweep with the heatsink mounted and cooling running, stepping the clock up to the rated frequency to catch chips that fail only under load. The mandatory factory rule is worth adopting at home: every repaired board re-tests from PT1 — no skipping stages.

Choosing and using a fixture

Bitmain's official test fixture (control board V2.1/V2.3) is FPGA-based, loads its configuration from an SD card, and requires the correct FPGA firmware version per model — an S21 needs the B047 version, for example. Third-party multi-model testers cover 40+ Antminer models on one rig, display the failing chip count and location directly, and cut diagnostic time several-fold compared with manual probing; some add per-chip temperature and voltage readouts. Whatever the brand, respect the support equipment: full-speed cooling fans during powered tests, adequately rated discharge resistors, a bench power supply or server PSU sized for the board's draw, and ESD protection throughout.

Why bench testing matters

Diagnosing inside an assembled miner is slow and ambiguous because cable, control-board, and PSU issues all masquerade as board faults. A dedicated fixture isolates the hashboard and gives repeatable, position-aware results — the difference between guessing and knowing. The fixture finds the fault; the rework tools fix it: see hot-air rework and reballing for chip replacement, and chip domain bypass for a salvage technique sometimes applied to faults the fixture locates. After any repair, the board goes back on the fixture and earns its way out through PT1, PT2, and PT3.