Antminer S21 Maintenance & Repair Guide

Introduction

The Bitmain Antminer S21 is the machine that redefined what efficiency means in Bitcoin mining. Packing 200 TH/s of SHA-256 hashrate into a chassis that sips only 17.5 J/TH, the S21 represented a generational leap when it launched in 2024 — and it remains one of the most capable air-cooled miners you can deploy today. If you are running one of these units, you are running cutting-edge silicon that Bitmain designed to compete at the absolute frontier of mining efficiency.

At the heart of the S21 sits the BM1368 ASIC chip — Bitmain’s 5nm-class powerhouse that packs more hashes per watt than any previous generation. Here is something that matters to the open-source mining community: the BM1368 is the same chip family used in the Bitaxe Supra, the 4th major revision of the fully open-source Bitaxe solo miner. The same silicon that drives institutional-scale hashing in a rack of S21s can sit on your desk in a Bitaxe, hashing away on WiFi. That is the beauty of open-source hardware — and it is the kind of connection that D-Central, as a pioneer in the Bitaxe ecosystem, cares deeply about.

This guide is your complete field manual for keeping the Antminer S21 running at peak performance. We cover routine maintenance that prevents problems, diagnostics that identify problems, and repair procedures that fix problems. Whether you are a home miner running a single S21 as a space heater supplement or an operator managing a rack of them in a dedicated facility, this guide gives you the knowledge to maintain your hardware like a professional.

Technical Specifications

Before you touch a screwdriver, know your hardware. The S21 is a significant architectural departure from the S19 series — different PSU connector, different control board processor, different heatsink design, different thermal management. Do not assume S19 procedures transfer directly.

S21 Family Variants

The S21 is the base model in a family of miners. While this guide focuses on the standard S21, much of the maintenance advice applies across the lineup:

The S21 Pro and S21 XP use the BM1370 chip — a further evolution of the BM1368. Hydro variants use a completely different cooling system and are outside the scope of this air-cooled maintenance guide.

Before You Begin

Safety Warnings

Summary of safety rules:

1. Power off and unplug before any maintenance. Wait 5 minutes for capacitor discharge.
2. Wear an ESD wrist strap grounded to the miner chassis whenever handling hashboards.
3. Let the miner cool for 10+ minutes after shutdown before touching heatsinks.
4. Work in a clean, dry environment — no liquids near the miner, no metal shavings, no conductive debris.
5. Never operate the miner with the top cover removed — airflow direction is critical for cooling.
6. Document everything — photograph cable positions and connector orientations before disconnecting anything.

Routine Maintenance

Prevention is cheaper than repair. A disciplined maintenance schedule extends the life of your S21, maintains peak hashrate, and prevents the catastrophic failures that turn a profitable miner into a paperweight. The BM1368 chips are designed for years of continuous operation — but only if you give them clean air, proper cooling, and stable power.

Recommended Maintenance Schedule

Visual Inspection

Start every maintenance session with a visual once-over. You are looking for the early warning signs of problems that will become expensive if ignored:

• Dust accumulation — The S21 moves a massive volume of air. Dust accumulates on fan blades, heatsink fins, and the intake grill. Heavy dust buildup restricts airflow, raises chip temperatures, and forces fans to spin faster (louder, shorter lifespan). In dusty environments (garages, basements, construction-adjacent areas), cleaning frequency should double.
• Discoloration on hashboards — Brown or yellow discoloration around components indicates overheating. This is a red flag that demands immediate investigation. Check for blocked airflow, failed fans, or degraded thermal paste.
• Corrosion on connectors — Green or white residue on Molex connectors, power cable pins, or Ethernet port indicates moisture exposure. Clean with IPA and assess your operating environment’s humidity.
• Physical damage — Bent heatsink fins, cracked PCB traces, loose screws, or damaged fan blades. Shipping damage is common — always inspect a new unit before first power-on.
• Cable condition — Check the flat ribbon cables connecting hashboards to the control board. These are fragile. A cable that has been pinched, bent at a sharp angle, or pulled can cause intermittent hashboard detection failures.
• PSU inspection — Look at the APW17’s input and output cables for fraying, heat damage, or loose connections. The PA45 connector should seat firmly without play.

Cleaning Procedures

Dust is the number one enemy of air-cooled miners. The S21’s four fans pull air through the chassis at high velocity — and they pull in everything floating in that air. Here is how to clean properly:

External Cleaning (Monthly)

1. Power off and unplug the miner. Wait 5 minutes.
2. Use compressed air to blow dust from the intake side (fan side) — blow from outside in, then from inside out to dislodge deep buildup.
3. Clean the exhaust side similarly.
4. Hold each fan blade still while blowing — letting fans spin freely under compressed air can damage bearings or generate back-EMF into the control board.
5. Wipe the exterior chassis with a dry, lint-free cloth.

Internal Deep Clean (Quarterly)

1. Power off, unplug, and wait 10 minutes for cooling and capacitor discharge.
2. Remove the top cover screws (Phillips #2) and lift the cover.
3. Put on your ESD wrist strap and clip it to the metal chassis.
4. Photograph the interior before touching anything — this is your reference for reassembly.
5. Use compressed air in short bursts (2–3 seconds) to blow dust from:
   • Heatsink fin arrays (blow perpendicular to fins to clear channels)
   • Between hashboards
   • Control board components
   • Cable connectors and sockets
6. Use a soft anti-static brush to gently dislodge any caked-on dust that compressed air cannot remove.
7. Inspect the heatsink mounting — ensure heatsink clips or screws are tight and the heatsink sits flush against the chips. Any gap here means thermal paste failure.
8. Reassemble in reverse order. Ensure the top cover is properly seated — the airflow path through the S21 depends on the enclosure being sealed.

Thermal Paste Replacement

The S21 uses thermal grease between the BM1368 chips and the aluminum heatsinks to transfer heat. Over time — typically 12–18 months of continuous operation — this thermal interface degrades: it dries out, develops micro-cracks, and loses thermal conductivity. The result is rising chip temperatures even when airflow is perfect.

Signs that thermal paste needs replacement:

• Chip temperatures consistently 5–10°C higher than when new (with same ambient temp and fan speed)
• Thermal throttling kicks in despite adequate airflow
• Individual chips running significantly hotter than neighbors on the same hashboard
• Visual inspection reveals dried, cracked, or unevenly distributed paste

Thermal paste replacement procedure:

1. Power off, unplug, wait 10 minutes, ESD strap on.
2. Remove top cover and carefully detach the heatsink(s) from the hashboard. The S21 uses clip-on or screw-mounted heatsinks — do not pry. If the heatsink is stuck to dried paste, gently twist while pulling straight up.
3. Clean old paste from both the chip surfaces and the heatsink contact surface using 99% isopropyl alcohol and lint-free cloths. Ensure no residue remains.
4. Apply fresh thermal paste to each chip. The S21 has 108 chips per hashboard — this is where a thermal paste stencil saves enormous time. The stencil ensures uniform thickness and coverage across all chips simultaneously.
5. Reseat the heatsink carefully. Apply even pressure — do not tighten one corner first. Diagonal tightening pattern for screws.
6. Repeat for all hashboards that need service.
7. After reassembly, power on and monitor chip temperatures for the first 30 minutes. You should see a noticeable drop — typically 5–15°C improvement.

Fan Maintenance

The S21 runs four fans — two intake, two exhaust — rated at 12V and 6.4A each. These fans are the first line of defense against thermal damage. When fans degrade, everything downstream suffers.

Fan health checks:

• Listen: Healthy fans produce a consistent high-pitched whine. Grinding, clicking, rattling, or intermittent speed changes indicate bearing wear.
• Watch: All four fans should spin at similar speeds. A visually slower fan is failing.
• Monitor: Check fan RPM in the miner dashboard. Healthy S21 fans typically run between 4000–6000 RPM depending on load and ambient temperature. A fan consistently below 3000 RPM under load is failing.
• Clean: Dust buildup on fan blades creates imbalance. This accelerates bearing wear and increases noise. Clean fan blades monthly.

Fan replacement indicators:

• Fan RPM drops below minimum threshold and triggers fan lost or fan speed error in logs
• Visible wobble or vibration during operation
• Fan does not spin up on power-on
• Bearing noise audible above normal operating noise

Diagnostics & Troubleshooting

When something goes wrong, you need data — not guesses. The S21 provides multiple diagnostic channels: LED indicators, the web dashboard, kernel logs via SSH, and the cgminer/bmminer API. Here is how to use all of them.

LED Status Indicators

The S21 control board has three LED indicators — green, red, and amber — that give immediate visual feedback on the miner’s state.

Startup sequence (normal): On power-on, both the fault (red) and running (green) LEDs light simultaneously during initialization. After initialization completes, the red light flashes while the miner connects to the mining pool. Once the pool connection is established, the red light goes off, the green light flashes steadily, and hashrate appears in the dashboard. This full sequence typically takes 3–5 minutes.

Web Dashboard Diagnostics

Access the S21’s web interface by navigating to the miner’s IP address in your browser. The default login credentials are root / root (change these immediately on first setup).

Key dashboard sections to check:

• Miner Status: Shows real-time hashrate per hashboard, total hashrate, and pool connection status. All 3 chains should show approximately 66.7 TH/s each.
• Hardware Status: Displays chip count per hashboard (should be 108 on each), PCB temperature, and chip temperature per board.
• Fan Status: RPM readings for all 4 fans. Look for significant variance between fans.
• Pool Status: Shows configured pools, accepted/rejected shares, and stale rates. A reject rate above 2% warrants investigation.
• System Log: The kernel log accessible from the web interface — same data you get via SSH.

SSH Diagnostic Commands

SSH gives you the deepest access to the S21’s diagnostics. These commands are your scalpel when the dashboard is too blunt.

# Connect via SSH (default credentials: root / root)
ssh root@MINER_IP_ADDRESS

# View the full kernel log (hardware events, errors, chain init)
dmesg

# View miner-specific log (S21 firmware)
cat /tmp/log/bmminer.log

# Filter for errors only
cat /tmp/log/bmminer.log | grep -i "error|fault|fail"

# Check hashboard chain status
cat /tmp/log/bmminer.log | grep -i "chain"

# View system uptime and load
uptime

# Check network connectivity
ping -c 4 8.8.8.8

# DNS resolution test
nslookup stratum.slushpool.com

# Check fan speeds (if accessible via sysfs)
cat /sys/class/hwmon/hwmon*/fan*_input

# View temperature sensors
cat /sys/class/hwmon/hwmon*/temp*_input

# Check running mining process
ps | grep -i "bmminer|cgminer"

# View system memory usage
free -m

# Check disk/flash usage
df -h

# Query miner summary from another machine on the same network
# Replace MINER_IP with your S21's IP address

# Get overall mining summary (hashrate, accepted, rejected, uptime)
echo '{"command":"summary"}' | nc MINER_IP 4028

# Get per-device (hashboard) stats
echo '{"command":"devs"}' | nc MINER_IP 4028

# Get pool connection status
echo '{"command":"pools"}' | nc MINER_IP 4028

# Get detailed stats (temperature, fan speeds, chip counts)
echo '{"command":"stats"}' | nc MINER_IP 4028

# Combined query — summary + devices + pools in one call
echo '{"command":"summary+devs+pools"}' | nc MINER_IP 4028

Common Error Codes & Messages

Here are the most frequent error messages you will encounter on the S21, what they mean, and how to fix them. For a comprehensive reference covering all Antminer models, see our Antminer Error Code & LED Reference Guide.

Hashboard Testing

When you suspect a specific hashboard, isolate it:

1. Identify the problematic board — the web dashboard shows per-chain hashrate and chip count. A board with 0 TH/s or fewer than 108 chips is your suspect.
2. Reseat the flat cable — power off, disconnect and reconnect the ribbon cable between the suspect hashboard and the control board. These connectors can work loose over time, especially after shipping or moving the unit.
3. Swap the cable position — connect the suspect hashboard to a different port on the control board. If the problem follows the hashboard, the hashboard is faulty. If the problem stays at the same port, the control board port is faulty.
4. Visual inspection — remove the hashboard and inspect under good lighting. Look for:
   • Burn marks or discoloration around chips or voltage regulators
   • Cracked solder joints (especially around the connector pins)
   • Swollen or leaking capacitors
   • Physical damage to PCB traces
5. Voltage domain check — with a multimeter, measure the voltage output to the hashboard chips (approximately 1.1V per domain). If voltage is absent or wildly off, the issue is in the power delivery circuit on the hashboard.

Common Repairs

Some repairs are within reach of a competent home miner with the right tools. Others require BGA rework stations, oscilloscopes, and years of board-level repair experience. We will be honest about that line — crossing it without the skills risks making a repairable board unrepairable.

Fan Replacement

Fan replacement is the most common S21 repair and the most approachable for DIY. The S21 uses four high-speed fans — two on the intake side and two on the exhaust side.

Procedure:

1. Power off and unplug. Wait 5 minutes.
2. Remove the fan guard screws on the affected side (Phillips #2).
3. Disconnect the fan power cable from the control board header. Note the connector orientation — these are keyed but it is still good practice to photograph first.
4. Remove the fan from the chassis.
5. Install the replacement fan with the airflow direction matching the original (arrow on fan housing indicates airflow direction). Intake fans blow INTO the chassis; exhaust fans blow OUT.
6. Reconnect the fan power cable to the correct header on the control board.
7. Secure the fan guard.
8. Power on and verify the new fan appears in the dashboard with a healthy RPM reading.

Power Supply Troubleshooting

The APW17 (1215a) PSU is purpose-built for the S21. It is a high-efficiency unit that converts 220–277V AC to 12–15V DC at enormous current. Power issues are the leading cause of cascading hardware failures.

Symptoms of PSU problems:

• Miner fails to power on entirely
• power fault or V_IN abnormal errors in logs
• Miner powers on but hashboards initialize intermittently
• Audible buzzing, clicking, or high-pitched whine from the PSU
• Miner resets under full hashrate load (PSU cannot sustain peak draw)

Troubleshooting steps:

1. Check wall voltage — measure with a multimeter at the outlet. Must be 220–277V AC. The S21/APW17 does NOT support 110V. Running on 110V will either fail to start or damage the PSU.
2. Inspect the power cord and PA45 connector — look for heat damage, melted plastic, or loose fit. The PA45 connector is specific to the S21 — a poor connection here causes voltage drop under load.
3. Measure PSU output — with the PSU disconnected from the miner but plugged into the wall, measure the DC output at the hashboard connectors. Should read between 12–15V DC.
4. Load test — a PSU can pass a no-load voltage test but fail under the S21’s 3500W draw. If the miner starts but crashes under full hashrate, the PSU may be degraded.
5. Swap test — if you have a second APW17, swap it in. This is the fastest way to confirm a PSU issue.

Hashboard Issues

Hashboard problems range from trivial (loose cable) to complex (dead ASIC chips requiring BGA rework). Here is the diagnostic ladder:

Level 1 — Cable and Connector (DIY-friendly):

1. Power off, unplug, ESD strap.
2. Disconnect and firmly reseat the flat ribbon cable on both ends (hashboard side and control board side).
3. Inspect connector pins for bent, corroded, or broken contacts.
4. Try a known-good flat cable if available.
5. Power on and check if the hashboard is detected.

Level 2 — Thermal and Mechanical (DIY with care):

1. Remove the hashboard and inspect heatsink mounting. If the heatsink is loose or can rock, the thermal interface has failed.
2. Remove heatsink and inspect thermal paste coverage. Replace if dried, cracked, or incomplete.
3. Check for physically damaged components — cracked chips, bulging capacitors, burnt areas.
4. Reseat heatsink with fresh thermal paste and power on.

Level 3 — Board-Level Repair (Professional required):

• Individual BM1368 chip replacement — requires BGA rework station, proper solder profile, and replacement chips.
• Voltage domain repair — failed MOSFETs, shorted capacitors, or damaged traces in the power delivery network.
• EEPROM replacement or reprogramming — requires specialized tools and calibration data.
• Signal chain diagnosis — CLK, CI, RI, BO, RST signal tracing requires an oscilloscope and deep knowledge of Bitmain’s chip communication protocol.

Network & Control Board Issues

The S21’s control board runs an Amlogic A113D processor and manages all hashboard communication, pool connectivity, fan control, and the web interface. When the control board fails, the entire miner goes down.

Common control board symptoms:

• Miner unreachable on the network (no ping response, no web interface)
• All hashboards show 0 chips despite good power and cables
• Fan control erratic — fans at 100% or 0% regardless of temperature
• Boot loop (green → red → off repeating) indicating firmware corruption
• Ethernet port LED not blinking when cable is connected

Troubleshooting steps:

1. Network isolation: Try a different Ethernet cable, a different switch port, or direct connection to your router. Verify the miner gets a DHCP lease or configure a static IP.
2. Power cycle: Unplug for 60 seconds, then power back on. Watch for the normal LED startup sequence.
3. Reset to defaults: If the web interface is accessible, use the “Reset” function under System settings. This resets pool/network config but preserves firmware.
4. SD card recovery: If the control board is in a boot loop, you may be able to flash stock firmware via SD card. Download the correct firmware version from Bitmain’s official site for the S21 model.
5. Control board swap: If all else fails, swapping in a known-good S21 control board is the definitive test. Control boards are model-specific — an S19 control board will not work in an S21.

Firmware & Software

Firmware Updates

Bitmain releases firmware updates for the S21 that can improve hashrate stability, fix bugs, add features, and patch security vulnerabilities. Keeping firmware current is basic operational hygiene.

How to update S21 firmware:

1. Download the firmware file only from Bitmain’s official support site. Verify the file is specifically for the S21 (not S21 Pro, not S21 XP — firmware is not cross-compatible within the S21 family).
2. Access the S21 web interface at http://MINER_IP.
3. Navigate to System → Firmware Upgrade.
4. Click “Choose File” and select the downloaded firmware file.
5. Click “Upgrade Firmware” and wait. The process takes 1–2 minutes. The miner will reboot automatically.
6. After reboot, verify the firmware version in the dashboard matches the update.
7. Reconfigure your mining pools if the update reset them (some updates do, some do not).

Third-Party Firmware Options

Several third-party firmware options exist for the S21 that offer features Bitmain’s stock firmware does not — autotuning, underclocking/undervolting for efficiency, enhanced monitoring, and pool diversification. Notable options include:

• Braiins OS+ — offers autotuning that optimizes each chip individually for maximum efficiency. Particularly useful for operators who want to undervolt for better J/TH and lower power bills.
• VNish — provides overclocking and underclocking profiles, enhanced monitoring, and custom fan curves.
• LuxOS — per-chip tuning and fleet management features.

Third-party firmware can void your Bitmain warranty. If you are within the warranty period, weigh the benefits carefully. Outside warranty? Third-party firmware is a legitimate tool for optimizing your operation — and it aligns with the Mining Hacker ethos of taking control of your hardware.

Configuration Best Practices

Pool configuration:

• Always configure all three pool slots — primary, secondary, and tertiary. If your primary pool goes down, the miner fails over automatically.
• Use Stratum V2 if your pool supports it — better efficiency, reduced bandwidth, and improved security.
• Consider pointing at least one backup pool to a decentralized option (Ocean, CK Pool, solo mining via ckpool) — this is how we keep Bitcoin mining decentralized.

Network configuration:

• Assign a static IP or DHCP reservation to your S21. DHCP lease expiration can cause brief mining interruptions.
• Use a wired Ethernet connection only — never WiFi bridges or powerline adapters for a miner pulling 3500W. Network instability costs you shares.
• Set a public DNS server (8.8.8.8 or 1.1.1.1) as backup if your router’s DNS relay is unreliable.

Security configuration:

• Change the default password from root/root immediately. Any device on your network can access the miner’s web interface if the default credentials are still set.
• If SSH is enabled, change the SSH password as well.
• If your miner is exposed to the internet (do not do this), set up a VPN instead.

Optimal Operating Environment

Power Requirements

The S21 draws 3500W continuously. This is not a device you plug into a standard household outlet.

• Circuit requirement: Dedicated 240V circuit, 20A minimum. At 240V and 3500W, the S21 draws approximately 14.6A. The electrical code in most jurisdictions (including Canada’s CEC) requires that continuous loads not exceed 80% of circuit rating — so a 20A circuit is the minimum, and a 30A circuit provides proper headroom.
• Outlet type: NEMA 6-20R or NEMA L6-30R, depending on your circuit. The APW17 ships with a specific power cord — verify compatibility with your outlet.
• Voltage stability: The APW17 accepts 220–277V AC. Voltage sags below 220V will trigger power faults. If your facility experiences voltage fluctuation, a power conditioner or UPS rated for 4000+ VA is recommended.
• Grounding: Proper earth ground is essential. An ungrounded circuit creates safety and ESD risks.

Cooling & Airflow

The S21 is air-cooled and depends on high-volume airflow through the chassis. The four fans move air from intake (left side, when viewed from front) to exhaust (right side). Everything between those fans — three hashboards loaded with 324 BM1368 chips — generates ~3500W of heat that must be removed continuously.

Guidelines:

• Ambient temperature: Keep below 35°C for optimal performance. The miner tolerates up to 45°C, but efficiency degrades and chip temperatures climb into the danger zone. In Canada, cold ambient air is your best friend — exhaust heat into a cold garage or basement for natural cooling advantage.
• Clearance: Maintain at least 30 cm (12 inches) clearance on the intake and exhaust sides. Obstructed airflow recirculates hot exhaust back into the intake — the fastest path to thermal throttling.
• Ducting: For home mining setups, ducting the hot exhaust outside (or into rooms you want to heat) is essential. A 6-inch inline duct fan connected to the exhaust side with a proper shroud is a proven setup. This is the dual-purpose mining approach — your S21 is a 3500W space heater that pays you Bitcoin.
• Never stack miners without a hot-aisle/cold-aisle separation. The exhaust of one miner must never feed into the intake of another.

Noise Management

At 75–83 dB, the S21 is louder than a vacuum cleaner and roughly equivalent to standing next to a busy road. This is not a living-room device.

• Isolated room: Garage, basement utility room, detached shed, or purpose-built mining enclosure.
• Sound insulation: Mass-loaded vinyl, acoustic foam, or insulated enclosures can reduce noise by 20–30 dB.
• Fan speed control: Third-party firmware (Braiins OS+, VNish) allows custom fan curves that reduce speed at lower ambient temperatures — quieter operation when conditions allow.
• Distance: Every doubling of distance from the miner reduces perceived noise by ~6 dB. Moving the miner from 1 meter to 4 meters away cuts perceived loudness roughly in half.

Advanced Diagnostics

Temperature Analysis

The S21 reports two temperature readings per hashboard:

• PCB temperature — measured by sensors on the circuit board. Maximum safe threshold: 81°C. Exceeding this triggers automatic shutdown (error code R:1).
• Chip temperature — estimated from chip behavior. Maximum safe threshold: 98°C. Exceeding this also triggers shutdown.

Healthy temperature ranges under typical operation:

If temperatures are consistently high:

1. Clean dust from heatsinks and fans
2. Verify all fans are spinning at spec RPM
3. Check for airflow obstruction (intake/exhaust clearance)
4. Measure ambient temperature — is the room too hot?
5. Inspect and replace thermal paste if the miner is 12+ months old
6. Consider underclocking via third-party firmware if ambient conditions cannot be improved

Hashrate Deviation Analysis

The S21 is rated at 200 TH/s ±3%. Healthy operation means seeing a real-time hashrate that fluctuates around 194–206 TH/s. Here is how to interpret deviations:

The Bitaxe Connection

Here is something worth understanding if you are a miner who cares about the open-source ethos: the BM1368 chip inside your S21 is the same chip family that powers the Bitaxe Supra — the 4th major revision of the fully open-source Bitaxe solo miner designed by Open Source Miners United (OSMU).

The Bitaxe Supra takes a single BM1368 chip and implements it on an open-source PCB that runs standalone over WiFi. Your S21 runs 324 of them on three hashboards connected to a proprietary control board. Same silicon, vastly different implementations — one proprietary and institutional, one open-source and sovereign.

D-Central has been a pioneer in the Bitaxe ecosystem since the beginning. We created the original Bitaxe Mesh Stand, developed leading heatsink solutions for the Bitaxe and Bitaxe Hex, and stock every Bitaxe variant alongside the full Nerd/Open-Source miner lineup. We sell BM1368 chips for both S21 repair and Bitaxe building.

If you are maintaining an S21 and want to experience what a single BM1368 chip can do in an open-source context — or if you want a Bitaxe running on your desk as a solo mining lottery ticket alongside your S21 doing the heavy hashing — D-Central has the full ecosystem.

Frequently Asked Questions

When to Call a Professional

This guide equips you to handle the maintenance and first-level repairs that keep your S21 running. But there is a clear line between “home maintainable” and “requires professional repair,” and knowing where that line is saves you from turning a repairable unit into scrap.

Call a professional when:

• Multiple ASIC chips need replacement (BGA rework station required)
• The hashboard has physical damage — cracked traces, blown components, burn marks
• EEPROM read failures persist after cable reseating (EEPROM chip replacement/reprogramming needed)
• Voltage domain measurements are abnormal (MOSFET, inductor, or capacitor failure)
• Control board does not respond to firmware recovery via SD card
• PSU makes arcing or burning sounds (do not open the PSU — dangerous capacitors inside)
• You are not confident in any step described in this guide

There is no shame in sending a board to a professional repair shop. The BM1368 is cutting-edge silicon, and the S21 hashboard is a dense, complex PCB. Board-level ASIC repair is a specialized skill that requires years of practice, expensive tools, and deep knowledge of Bitmain’s proprietary designs.

Interactive Hashboard Schematic

Explore the ANTMINER S21 hashboard layout below. Toggle layers to isolate voltage domains, signal chains, test points, key components, and thermal zones. Hover over any region for quick specs — click for detailed diagnostics, failure modes, and repair guidance.