Prusa Research Prusa i3 MK3/S/+ to MK3.9S Upgrade Kit - Silver PSU - 2+3 Screws (Power Cable Connected With Screws)

Which PSU Does Your 3D Printer Have?

• Black PSU - Kit is compatible as is.
• Silver PSU - you will need to add a compatible wiring harness or a black PSU (in the configuration box above).

How Many Screws Does Your Heatbed Have?

• 2+3 screws (power cable connected with screws) - Kit is compatible as is.
• 2+1 screws (power cable soldered) - replacing the bed will be necessary.

Gain Speed and Maintain Quality

Every upgrade kit includes Prusa's 32-bit xBuddy electronics board, unlocking Input Shaper and Pressure Advance for dramatically faster 3D printing speeds. Prints that once ran overnight can now be finished in just a few hours — all while maintaining the same exceptional print quality.

• Input Shaper cancels frame vibrations to eliminate ghosting and ringing at high speeds.
• Pressure Advance fine-tunes extrusion for clean corners and sharp details, even on fast prints.
• Prints up to 2× faster than the original MK3S/+ with no loss in quality.

Customized Control

Every upgrade kit includes a vibrant 3.5″ color xLCD that makes navigating menus, previewing files, and managing your printer faster and more intuitive than ever.

• Preview print files, read on-screen instructions, and scan QR codes directly from the LCD.
• Customize the always-visible status footer to display the information you care about most.
• Use standard USB flash drives for G-code storage and firmware updates.
• Flash firmware remotely via Prusa Connect — or the old-fashioned way with a USB drive.

Next-Generation Extrusion

The MK3.9S and MK4S kits include Prusa's Nextruder — a completely redesigned extruder featuring an integrated load cell for automatic first-layer calibration, a quick-swap hotend, and a high-flow CHT nozzle that delivers up to 114% more flow. Combined with a high-performance 360° cooling system, you get faster prints, better overhangs, and easier maintenance.

• Integrated load cell eliminates manual Live Adjust Z — perfect first layers, every time.
• Quick-swap hotend design lets you change nozzles in seconds with two thumbscrews.
• High-flow 0.4 mm CHT nozzle enables faster printing and stronger, more durable parts.
• 360° cooling fan and shroud deliver precise airflow for improved overhang performance.

Ultra-Precise Motors for Flawless Surfaces

The MK4S kit includes high-precision 0.9°-per-step (400-step) X/Y stepper motors, specifically engineered to eliminate Vertical Fine Artifacts (VFAs) — the subtle surface imperfections visible on close inspection. The MK3.9S reuses your existing motors and gets remarkably close, but the MK4S motors are the finishing touch for truly flawless surfaces.

• MK3.9S users can purchase the precision motors separately to complete a full MK4S upgrade later.
• 0.9° per step (400 steps) delivers smoother, more precise motion on the X and Y axes.
• Eliminates VFAs (Vertical Fine Artifacts) for the smoothest possible print surfaces.
• Upgrade path available: MK3.9S owners can add precision motors later to match MK4S quality.