Avalon 1566 – Temperature Too High

Pull the power cord, wait 60 seconds for bulk capacitors to drain, then restart. A full cold-boot clears any wedged firmware state around the OVER_TEMP trip flag - Canaan's MM3+ build occasionally holds the fault across a soft reboot. Count to 60 seconds; do not just hit the dashboard restart. This step alone clears roughly one in five events on a 1566 that saw a transient thermal spike (warm intake air for ten minutes, a neighbour's appliance on the same HVAC circuit). If the miner boots clean and runs an hour without re-tripping, you caught a transient. If it re-trips within minutes, escalate.

Vacuum the front intake grille and rear exhaust vent with a shop-vac using the soft-brush attachment. Pay particular attention to the four HA1250H12SB-Z fan blades and the heatsink fin packs visible through the grille. Dust-packed fins on a 1566 raise the heatsink-to-ambient delta by 8-15 C, which is the entire margin between running fine and OT on a warm day. Do not use a hard nozzle; you are moving dust, not polishing chassis steel. Restart and run for one hour - clean intake alone resolves a large fraction of 1566 OT events, especially on miners with six or more months of uncleaned service.

Measure intake-air temperature with an IR thermometer or probe thermometer held 5 cm from the front grille during hashing. Target 30 C or below for a Canadian basement or garage install; 35 C is the Canaan absolute maximum per the 1566 datasheet (-5 C to 35 C spec). If intake reads above 30 C, open a window, crack the garage door, or move the miner's intake to a cooler corner before touching the miner. You cannot fix an ambient-envelope problem at the miner.

Confirm physical clearance: at least 30 cm in front of the intake, at least 15 cm behind the exhaust. A 1566 moves roughly 750 CFM of air under load - even a curtain 10 cm away throttles intake. A 1566 on a shelf with no breathing room recirculates its own 70 C+ exhaust. Pull everything back from the miner. Clearance is free, use it. Restart and confirm under load.

If you run multiple miners in a shed or garage, reconfirm airflow direction. Miners aimed at each other's intakes cook each other. Correct 1566 layout is cold intake from the front on a dedicated cold-air plenum, exhaust to outside or into a heat-utilisation duct for home heating. Recirculating the miner's own exhaust into its intake is the fastest way to hit OT in any install, but particularly in a heated Canadian basement from November through April.

Open the chassis, remove each of the four HA1250H12SB-Z fans in turn, and spin them by hand. A healthy dual-ball-bearing fan spins freely for 2-3 seconds after a flick. A failing fan grinds, buzzes, or stops immediately. Replace any fan that fails this test with a drop-in HA1250H12SB-Z (12 V, 9.0 A, 96 W rated). The 1566 uses the same fan as the 1346, 1366, and 1466 - one spare SKU covers the whole A13/A14/A15 generation. Parts available from Zeus Mining, bit2miner, or a D-Central parts order.

Measure the 12 V fan rail at the PSU-to-control-board connector under load. Expect 11.8 V to 12.2 V sustained. Below 11.6 V means a tired PSU sagging the fan rail - fans slow, chips heat, miner trips OT, and you chase a thermal fault that is actually a power fault. Swap to a known-good PSU from the 1346/1366/1466/1566 family (same 4100 W / 11.5-15 V DC product line) before assuming the miner is the problem. Do NOT use an older A11/A12-era PSU: the control signaling differs and the rail voltage specification is not cross-compatible.

Re-torque the heatsink mounting clips on each of the three hashboards. Canaan's heatsink clip design across the A13-A15 generation loosens over 12-18 months of thermal cycling. A heatsink with even 0.1 mm of lift loses paste contact and the chip underneath cooks while its neighbours are fine. Remove the heatsink, wipe off the old paste with 99% IPA, apply a thin uniform layer of Arctic MX-6 or Thermal Grizzly Kryonaut, reseat with even clip pressure. Do one hashboard at a time so you do not mix clips.

Install a foam pre-filter on the intake if your install does not already have one. D-Central strongly recommends a simple foam pre-filter on every 1566 install - it catches dust before it hits the heatsinks, and you can vacuum or wash it in seconds instead of opening the chassis. Without a pre-filter, you rely on the heatsink fins themselves to catch debris, which is the failure mode Step 2 fixes.

Verify line voltage at the outlet under load. On 240 V split-phase (the correct feed for a 1566's 3420 W draw) expect 235-245 V. On 208 V commercial expect 202-212 V. The 1566's PSU accepts 220-277 V AC input - a feed sagging under 230 V forces the PSU to draw more current, heats PSU internals, and can trip the PSU thermal sensor independently of the hashboard sensors. If line voltage is low, fix the feed before continuing - that is an electrician or panel problem before it is a miner problem. 120 V 15 A circuits will NOT sustain a 1566; do not attempt.

Snapshot cgminer-api estats output to a text file before any further changes. Run `echo -n '{"command":"estats"}' | nc 127.0.0.1 4028` from the miner or a network-connected laptop. Save as 1566-pre-fix.txt. If the miner ends up shipping to D-Central, that pre-fix snapshot is exactly what the bench tech wants to see. It saves diagnostic time, which saves you repair dollars - usually 30-60 minutes of bench labour.

Remove a hashboard, strip the heatsinks, and reapply thermal paste on every ASIC on the chain that dominated your PVT_T outlier list. Use Arctic MX-6 or Thermal Grizzly Kryonaut in a thin uniform layer - the grain-of-rice heuristic is for CPUs, not a 120-chip hashboard; you want a uniform film across each chip top. Replace any thermal pad under the PCH or voltage-domain ICs if pads are crumbled, discoloured, or compressed. Budget one hour per hashboard the first time, 30 minutes once practised.

If one specific chip position is the outlier and paste refresh did not resolve it, reflow that single chip. Preheat the hashboard from below at approximately 150 C for 3 minutes, hot-air from above at 310-330 C for approximately 30 seconds with flux around the chip periphery, natural cool-down. The A3206-family BGA tolerates a single reflow cycle reliably - behaviour tracks the A3205 on the 1346. A second reflow on the same chip within 90 days rarely sticks; at that point the chip is dying and needs replacement.

Flash a known-good MM3+ firmware build from Canaan's firmware portal at avalonminer.org/firmware-document/. The portal is login-gated and release notes are sparse, but it is the only official source for MM3+ builds. Verify your hardware revision against the firmware compatibility table before flashing - the wrong MM3+ for a late-rev 1566 can brick the control board. Flash via the dashboard's firmware page over a stable wired connection; never flash over wireless, never flash while hashing.

Reseat the control-board ribbon connectors on all three hashboards. IDC-style ribbons on the 1566 MM3+ oxidize the same way as the 1246/1346 ribbons in humid environments. Pull each ribbon fully, wipe contacts with 99% IPA on a lint-free wipe, reseat until the latch clicks. Oxidized ribbons can break the temperature telemetry path specifically, causing a chain to appear cool while running hot - tripping a different sensor and confusing diagnosis.

Inspect capacitors on the voltage domain under the heatsinks. Bulging electrolytics or cracked MLCCs near the PMICs = time to replace. Caps on a 1566 should not be showing age yet at 18 months; if they are, it points at sustained PSU ripple or over-voltage events upstream. Replace caps with Panasonic FR / Nichicon HD / Rubycon ZL grade equivalents, then retest. Stop DIY here if you do not own a hot-air station and some solder-rework miles.

Stop DIY and ship to D-Central when any of the following are true: every fan replaced, every heatsink cleaned, every chip repasted and the miner still trips OT within 24 hours; reflowed a chip once and OT returned within 30 days; PVT_T[] returns impossible values (negative, above 200 C, or identical across all positions on a chain); same chip position trips on two different 1566 units in your rig; visible discoloration, burnt smell, or capacitor damage anywhere on the hashboard or MM3+. Book a D-Central ASIC Repair slot. Turnaround 5-10 business days, Canada-wide shipping, US and international welcomed.

Pack for shipping: anti-static bags on each hashboard and the MM3+ separately, double-box with at least 5 cm of foam on every side, include a printed diagnostic note with the kern.log excerpt (actual OT lines), MM3+ firmware build, PSU model, measured line voltage, intake ambient, fan tach readings before failure, and every Tier 1-3 step you have already run. The bench tech starts from your notes - better notes, faster and cheaper repair. Never ship hashboards loose or in single-box packaging; A3206-family BGAs do not survive careless handling.