LM317MDCYR L4 - Adjustable Voltage Regulator for Antminer S21 T21 Hashboard

LM317MDCYR (L4) 500mA Adjustable Voltage Regulator – Antminer S21 / T21 Hashboard Repair

The LM317MDCYR (board markings L4) is a 500mA adjustable positive linear voltage regulator in a SOT-223 SMD package, used as the local low-current bias regulator on Antminer S21 and T21 hashboards. It generates an adjustable output between 1.25V and 37V set by an external resistor divider — typically configured for 1.8V or 3.3V on Bitmain hashboards. Failure mode is usually a thermal-shutdown short or a stuck output voltage.

Where the LM317M Sits on the S21 / T21 Board

On the S21 and T21 control areas, the LM317MDCYR feeds a small, sensitive bias rail — usually for a level translator or for the auxiliary side of a DC-DC controller. Because it is a linear regulator (not switching), the rail it produces has very low ripple, which is what some sensitive analog blocks need to operate correctly. When this part fails, the dependent block goes silent and the controller logs an initialization error.

Replacement Procedure

Pre-heat the board to 130-150°C. Remove the failed LM317MDCYR with hot air at 320°C — the SOT-223 has a large thermal tab on the back, so use enough heat to fully reflow that tab. Clean the pads with flux and braid. Place the new chip with pin 1 aligned to the silkscreen, reflow at 320°C, and confirm the tab joint with a gentle nudge after cool-down. Bench-test the regulated rail before reassembly.

LM317MDCYR Specifications

Related Voltage Regulators

• LM317MBSTT3G 500mA Adjustable Regulator – Antminer S21/T21
• LM317LD13TR Adjustable 3-Terminal Regulator
• ASPL317LDT-R Adjustable Positive Regulator
• SPX5205M5 1.8V LDO – Hashboard Chip

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