Whatsminer M60S – PSU Efficiency Drop

Reboot from a cold AC-off. Kill power at the PDU for a full 10 minutes — long enough for primary-side caps to bleed — then cold-boot. Some `psu_status` fault bits latch until AC is fully removed; a soft restart via dashboard will not clear them. Observe whether the fault bit returns within the first 30 minutes of hashing. If it clears and stays clear for 24 hours, you had a transient thermal event and no further action is needed.

Export and read power.log. WhatsminerTool V9.0.1 → Remote Ctrl → ExportLog. Open power.log in a plain-text editor. Search every occurrence of `psu_status`. Record the full hex word and timestamp across a 30-minute window of full-load hashing. This step is diagnostic, not corrective — but without the hex word you are guessing. The dashboard shows a decimal code; power.log shows the actual bit pattern and is diagnostically more specific.

Verify intake airflow and ambient at the PSU grille — not room-middle, not hallway, at the PSU intake. Target ambient ≤ 30 °C for standard M60S, ≤ 35 °C for hydro variants. Rack layouts that put one miner's exhaust near the next miner's PSU intake create a heat-recirculation loop. Re-plumb airflow or rebalance rack spacing; this often recovers 2-4% of efficiency with zero parts cost.

Clean the PSU intake grille externally. Dust across the grille adds static pressure, drops fan throughput at the same RPM, and raises internal PSU temperature. Shop-vac from outside, soft-bristle brush the grille, wipe with dry microfiber. Do not open the PSU for this pass — clean what you can reach externally. A clogged grille easily adds 8-15% to PSU internal temperature without tripping any code.

Check MicroBT firmware version and cross-reference community known-issue lists (r/BitcoinMining, BitcoinTalk, Discord). If on a build flagged for PSU-telemetry drift, roll one version forward or back and re-baseline efficiency. Do not cross-flash firmware from M30S or M50S — hardware revisions differ. Pin the version across your fleet once you've confirmed a clean build.

Replace the PSU intake fan — the fix for roughly 60% of M60S efficiency complaints. Kill AC at the PDU, wait 10 minutes for primary caps to bleed (~400 V DC stored). Open the PSU enclosure (Phillips #2). The intake fan is a ~120 mm 4-pin PWM unit. Note wire colour and tach polarity before disconnecting. Install a replacement of equivalent airflow spec — verify CFM and static pressure against the original's sticker before ordering. Reassemble, cold-boot, verify RPM reads back into the 4,200-5,500 band under load.

Re-seat every PSU connector. Power off, confirm cap drain. Re-seat the AC inlet IEC connector inside the case, the PSU-to-busbar DC output bolts (torque to manufacturer spec), the I2C telemetry cable to the control board, and the PSU fan connector. Oxidation on any of these adds contact resistance that shows up as connection heat and as wall-plug efficiency drift. Any discoloured or heat-blackened connector is a replacement, not a re-seat.

Measure the hashboard rail at the busbar under full load. Multimeter on DC, probe directly at the copper busbar where it lands on each hashboard. Expect 14.5 V ± 0.3 V (confirm exact target against the PSU's output label — varies slightly by revision). If the rail sags below 14.2 V under full hashing load, the PSU is losing regulation and hashboards compensate with higher current, which wastes watts as heat at the PSU-to-board path. A sagging rail that recovers after a fan swap confirms thermal-induced regulation drift.

Log the AC inlet with a logging clamp meter (Hioki, Fluke 345, UNI-T UT-230C) for 24 hours. Two patterns to spot: (a) voltage sag during peak hours below 225 V residential / 202 V commercial; (b) current spikes correlated with sag — if voltage drops and current rises in lockstep, the PSU is compensating and the circuit is undersized. Either pattern means the fix is upstream of the PSU.

Re-apply thermal paste to the PSU PFC MOSFETs and rectifier bridge. Remove the PSU, separate PCB from heatsink, clean old paste with IPA 99%, apply a thin uniform layer of Arctic MX-6 or Thermal Grizzly Kryonaut to the MOSFET and rectifier die-to-heatsink interface. Replace any thermal pads on voltage-domain ICs with fresh pads of equivalent thickness. Reassemble. Typically recovers 5-10 °C of headroom on PSU internal temperature.

Validate with a known-good PSU swap. If you have two M60S chassis, swap PSUs between them for 60 minutes of full-load operation each. Log efficiency and psu_status on both. Fault follows the PSU → PSU is root cause → Tier 3 if fan and paste didn't fix it. Fault follows the chassis → control board or I2C telemetry. No fault either way → the problem was in the original PSU-to-chassis interconnect.

Replace aged electrolytic caps on the secondary side. Primary-side PFC caps (typically 470 μF 450 V Nichicon PW / Rubycon ZLH class) and secondary-side output caps are the usual ESR-drift suspects. Bulging, brown crust around the base, or dome-up geometry = replace. Match voltage rating (or higher), capacitance, ESR (or lower), ripple-current rating (or higher), 105 °C temperature class. Replace the whole bank — mixing new and old in one filter stage creates its own instability.

Replace PFC MOSFETs and output rectifiers if internal temperature has been sustained above 85 °C. Extended over-temp operation accelerates MOSFET degradation — RDS(on) climbs, switching losses rise, efficiency drops further. If the PSU was pulled on thermal protect (0x0080) multiple times, plan on MOSFET replacement even if the part passes continuity; damage is in the on-resistance drift. Match original part numbers exactly.

Pin an exact firmware version with clean community reports for M60S telemetry accuracy. Do not chase 'latest' if 'latest' has open PSU-telemetry bugs. Document the version on your ops wiki; use the same version across all M60S units for consistent J/TH baselining. Flash via WhatsminerTool `Upgrade Firmware`, not the web UI — the tool workflow is more reliable on partial-upgrade recovery.

Schedule bench validation under a programmable load. After cap-and-MOSFET rework, do not reinstall the PSU live for burn-in — use an electronic load at ~3400 W for a 24-hour soak. Log output voltage stability, fan RPM, internal temperature, and any hex-bit faults. A repaired PSU that holds 14.5 V ± 0.2 V across the soak with no code is ready. A PSU that drifts or faults in the first two hours is not repaired.

Stop DIY and ship. Ship when: (a) PSU faults during a programmable-load soak after your best rework, (b) you measure primary-side short on PFC rectifier or MOSFETs, (c) you see visible burn damage on PCB traces, (d) you've replaced the fan, cleaned the thermal path, and re-capped the secondary but efficiency is still above 20 J/TH. Book a D-Central ASIC Repair slot — Canadian bench, OEM or equivalent parts, 24-hour nameplate burn-in included.

D-Central bench process. Full PSU teardown, programmable-load validation to MicroBT spec, controller IC replacement with OEM or equivalent, optocoupler swap when feedback loop is suspected, PCB trace repair where heat or arc damage is present, 24-hour nameplate soak before the unit is returned. Where a PSU is beyond economic repair, we stock compatible M60S-family replacement supplies with Canadian warranty and bilingual support.

Ship safely. Kill AC at the PDU 24 hours before packing — primary-side caps store charge; give them time. Anti-static bag, then foam with ≥ 5 cm on every side, double-boxed. Include a printed note: observed symptoms, firmware version, the power.log snippet pulled in step 2, and your contact. This saves us diagnostic time, which saves you money. Canadian customers ship bench-direct; US and international welcomed.