Antminer S21 Power Supply Troubleshooting

Step 1: AC Input Verification

Before diagnosing the PSU, verify the AC supply is correct:

1. Check your outlet voltage with a multimeter set to AC voltage (VAC range):

   • Expected: 200–240V AC (the APW17 does NOT operate at 110V for full power)
   • If your region has 110V, you need a 240V circuit or a step-up transformer

2. Check the AC power cord:

   • Inspect for damage, frayed insulation, or loose connections
   • Try a known-good C13/C14 power cord
   • Verify the cord is rated for at least 16A

3. Check the AC input at the PSU:

   • Using a non-contact voltage tester, verify AC is present at the PSU input
   • If your facility has GFCI/RCD breakers, verify they have not tripped

Step 2: Standby Voltage Check

The APW17 has a standby circuit that provides 12V whenever AC power is connected, even before the miner is commanded to start mining:

1. Connect the AC cord to the PSU (do NOT connect hashboards yet)

2. Measure the 12V standby at one of the output connectors:

   • Set multimeter to DC voltage (20V range)
   • Red probe to a 12V pin on any output connector
   • Black probe to a ground pin
   • Expected: 11.8–12.2V

3. If standby voltage is 0V:

   • The PSU's internal standby converter has failed
   • Check the AC input fuse inside the PSU (requires opening — qualified personnel only)
   • The PSU likely needs replacement

4. If standby voltage is low (under 11V):

   • The standby converter is weak — PSU is degrading
   • Check AC input voltage (low AC input = low DC output)
   • Replace the PSU

Step 3: Output Voltage Under Load

The PSU must maintain 12V under the full mining load (~300A):

1. Connect all three hashboards and the control board

2. Power on the miner

3. Wait for mining to start (2–3 minutes after boot)

4. Measure the 12V output at the PSU connector while mining:

   • Expected: 11.4–12.6V (12V ±5%)
   • Below 11.4V: PSU is sagging under load — check AC input, consider PSU replacement
   • Above 12.6V: OVP may trigger, indicating a feedback circuit issue

5. Measure at each hashboard power connector individually:

   • Voltage should be within 0.2V of each other
   • A significantly lower reading on one connector indicates a bad cable or connector

Under-voltage symptoms:

• Hashboards detected but with low hashrate
• Random chip drops during mining
• Miner reboots under load
• "Power supply fault" error in web dashboard

Step 4: Protection Circuit Testing

The APW17 has four protection circuits. When any triggers, the PSU shuts down output:

Over-Voltage Protection (OVP):

• Triggers if output exceeds ~13.2V
• Indicates failed voltage regulation
• PSU needs replacement or internal repair

Over-Current Protection (OCP):

• Triggers if load exceeds ~330A
• Can indicate a shorted hashboard drawing excessive current
• Disconnect hashboards one at a time to identify the culprit
• If OCP triggers with no hashboards connected, the PSU is faulty

Over-Temperature Protection (OTP):

• Triggers if internal PSU temperature exceeds safe limits
• Check PSU fan operation (should spin when AC is connected)
• Check for dust buildup blocking PSU airflow
• Verify ambient temperature is below 40°C

Short-Circuit Protection (SCP):

• Triggers immediately if output is shorted to ground
• Disconnect all loads and check for shorts on the output cables
• Inspect hashboard power connectors for bent pins causing shorts

Step 5: Fan and Thermal Check

The APW17 has an internal fan that runs whenever AC power is connected:

1. Fan not spinning: Listen for the fan when AC is connected. If silent:

   • The internal fan has failed — PSU will overheat and trigger OTP
   • PSU needs fan replacement (requires disassembly by qualified technician)

2. Fan running but PSU overheating:

   • Check for dust accumulation inside the PSU (blow out with compressed air through the vents)
   • Ensure adequate clearance around the PSU for airflow (at least 5cm on all sides)
   • Check ambient room temperature — if above 35°C, improve cooling

3. Abnormal fan noise:

   • Grinding or clicking sounds indicate bearing failure
   • Replace the fan before it seizes and causes OTP shutdown

Step 6: Connector and Cable Inspection

Power connectors are a common failure point due to the high currents involved:

1. Inspect all power connectors for:

   • Blackened, burnt, or melted plastic (indicates overheating from poor contact)
   • Oxidized or tarnished pins (reduces conductivity, causes localized heating)
   • Loose fit (the connector should click firmly into place)
   • Bent or pushed-back pins

2. Measure voltage drop across connectors:

   • While mining, measure the voltage at the PSU output AND at the hashboard input
   • The difference should be less than 0.3V
   • A larger drop indicates a high-resistance connection (bad connector, damaged cable)

3. Cable inspection:

   • Check for damaged insulation, especially where cables bend near connectors
   • Look for discoloration (heat damage) along the cable length
   • Verify wire gauge is appropriate (the stock cables are correctly sized)