S19j Pro Hashrate Drift After 18 Months in a Guro Basement
Field measurements on fourteen Antminer S19j Pro units show how inlet dust and voltage sag affect second-generation output in Seoul basement hosting.
Fourteen S19j Pro units arrived at our workshop in January 2026 after running continuously in a Guro-gu basement since mid-2024. The operator suspected gradual hashrate loss but had no per-unit logs. We ran each machine for 48 hours at 25°C inlet with clean filters.
What We Measured
Nominal spec for the S19j Pro is 104 TH/s at 3068 W. Eleven units landed between 99.2 and 102.8 TH/s — within the 5% band we consider acceptable for second-generation hardware with original hashboards. Three units measured below 95 TH/s.
Dust and Airflow
The basement intake drew air from a parking ramp. Fine concrete dust had coated the front fan grilles on every unit. After external cleaning only (no hashboard disassembly), two of the three underperformers gained roughly 2 TH/s. The third showed a failing fan on hashboard slot 2, confirmed by RPM variance above 15%.
Voltage Notes
The facility fed 218–219 V at the rack PDU during our visit. Units on the same circuit as a water heater compressor showed brief sags to 212 V during compressor cycles. We recommended a dedicated breaker for the mining row — a ₩200,000 electrician visit that often costs less than replacing one hashboard.
Takeaway for 2026 Operators
Second-generation S19j Pro units remain viable above the 0.05 TH/s floor when inlet air stays below 30°C and voltage remains stable. Basements without filtered intakes should budget quarterly grille cleaning as routine maintenance, not an emergency repair.