## Overview
[Schematic](https://www.prusa3d.com/downloads/Electronics_drawings/FDM-MK4-LoveBoard-38.pdf)
released under CC-BY-SA 4.0 (Attribution-ShareLike 4.0 International)
Allows Commercial Use.
Therefore, derivatives must also be licensed under this if they materially use the original schematic.
## LoveBoard Schematic Component Listing
| **Designator** | **Part / Value** | **Description** | **Notes** |
| -------------- | -------------------------- | --------------------------------- | ------------------------- |
| **ICs** | | | |
| U1 | NCP1117ST33T3G | LDO Regulator, 3.3 V, 1 A | SOT-223 |
| U2 | HX-717 | 24-bit ADC (Load Cell / Pressure) | Pressure sensor front-end |
| U3 | ST490ABDR | RS-422 / Differential Line Driver | MAX490EESA equivalent |
| U5 | AT21CS11-STU10-T | 1 kb EEPROM, 1-Wire | Serial number |
| **MOSFETs** | | | |
| Q3 | MMBF170 | N-MOSFET, 60 V | |
| Q4 | MMBF170 | N-MOSFET, 60 V | |
| Q5 | MMBF170 | N-MOSFET, 60 V | |
| **Diodes** | | | |
| D1 | BAV99W.115 | Dual switching diode | |
| D2 | BAV99W.115 | Dual switching diode | |
| D3 | LED, Red (LST-C193KRKT-5A) | Status LED (DNF) | |
| D4 | LED, Red (LST-C193KRKT-5A) | FAN-0 LED (DNF) | |
| D5 | LED, Red (LST-C193KRKT-5A) | FAN-1 LED (DNF) | |
| D6 | LED, Red (LST-C193KRKT-5A) | Heater LED (DNF) | |
| D7 | SMAJ5.0A | TVS Diode, 5 V | |
| D10 | BAV99W.115 | Dual switching diode | |
| **Resistors** | | | |
| R1 | 1 kΩ | 1-Wire pull-up | |
| R2 | 10 kΩ | ADC reference | |
| R3 | 100 Ω | Differential termination | |
| R4 | 100 Ω | Differential termination | |
| R5 | 8.2 kΩ | ADC front-end | |
| R6 | 590 Ω | ADC front-end | |
| R7 | 8.2 kΩ | ADC front-end | |
| R8 | 1 kΩ | NTC hotend pull-up | |
| R9 | 33 kΩ | NTC heatsink pull-up | |
| R10 | 10 kΩ | Fan tach pull-up | |
| R11 | 1 kΩ | FAN-0 LED (DNF) | |
| R12 | 100 Ω | MULTIWIRE series | |
| R14 | 620 Ω | 3.3 V LED resistor (DNF) | |
| R22 | 220 Ω | RS-422 SCK | |
| R23 | 220 Ω | RS-422 DATA | |
| R27 | 10 kΩ | ADC SCK pull-up | |
| R28 | 10 kΩ | ADC reference | |
| R30 | 1 kΩ | FAN-0 LED (DNF) | |
| R31 | 1 kΩ | FAN-1 LED (DNF) | |
| R32 | 10 kΩ | Heater LED (DNF) | |
| **Capacitors** | | | |
| C1 | 10 µF | ADC supply | |
| C2 | 100 nF | ADC supply | |
| C3 | 100 nF | ADC input | |
| C4 | 10 µF | +5 V bulk | |
| C5 | 100 nF | 3.3 V decoupling | |
| C7 | 100 nF | Differential | |
| C11 | 100 nF | ADC input | |
| C13 | 10 µF | LDO input | |
| C15 | 100 nF | Heater supply | |
| C16 | 100 nF | RS-422 Vcc | |
| C18 | 1 µF | +5 V bulk | |
| C19 | 10 µF | LDO output | |
| C24 | 100 nF | ADC AVDD | |
| **Inductors** | | | |
| L1 | 120 Ω @100 MHz / 3 A | | |
| L2 | 120 Ω @100 MHz / 3 A | | |
| L3 | 120 Ω @100 MHz / 3 A | | |
| L4 | 120 Ω @100 MHz / 3 A | | |
| L5 | 120 Ω @100 MHz / 3 A | | |
| L6 | 120 Ω @100 MHz / 3 A | | |
| L7 | 120 Ω @100 MHz / 3 A | | |
| L8 | 120 Ω @100 MHz / 3 A | | |
| L10 | 120 Ω @100 MHz / 3 A | | |
| L11 | 120 Ω @100 MHz / 3 A | | |
| **Connectors** | | | |
| J1 | 502584-0260 | NTC Hotend | |
| J2 | 502585-0370 | Filament sensor | |
| J4 | 502585-0470 | Extruder Motor | |
| J12 | 502584-0260 | NTC Heatsink | |
| J13 | 503154-2290 | Board-to-board | |
| J14 | 502585-0470 | Load Cell | |
| FAN1 | 502584-0360 | Fan 0 | |
| FAN2 | 502584-0360 | Fan 1 | |
| P1 | 43650-0212 | Heater output | |
## Gareth's Analysis
```
The HX717 is connected to what I believe is a [ST490AB](https://www.st.com/en/interfaces-and-transceivers/st490ab.html) chip which converts it to [RS-422](https://en.wikipedia.org/wiki/RS-422). (The chip says “S490AB MZ306”) The PD_SCK and DOUT pins are hooked up this, effectively ground isolating the chip from the main board. Pictures of the cable show white/blue twisted pairs in this location which is the expected wiring. I’m pretty sure I can still talk to it via 2 regular I/O pin and an associated ground wire.
Fans are reversed from how the Chinese boards normally do PWM. Here the + pins are pulsed but on boards like the Octopus its usually the ground pins that pulse. The ground pin is connected to the relay/transistor network on the board so just swapping the wiring is likely impossible. Also using 12V fans is probably also out. (If I’m wrong about this Id be happy to hear it! Also if you have any ideas for a work around) Luckily I don’t think the board relies on the fan power for anything but the associated indicator LEDs so it could all be bypassed.
The unidentified pins (5,15 &17) are probably the Filament Sensor, and 2 signal lines for fan failure. The fan RPM lines go into the relay/transistor network and I think they are reducing the RPM signal to a binary on/off signal so they don’t have to read it with an ADC back on the main board. I cant trace the filament sensor output line at all. I should be able to work out what these do for certain once I get power to the board. But if this is what they are, they are not essential pins.
_Update:_ Prusa published the schematics: [https://www.prusa3d.com/downloads/Electronics_drawings/MK4_electronics_schematics.zip](https://www.prusa3d.com/downloads/Electronics_drawings/MK4_electronics_schematics.zip)
The Filament sensor is connected to the B channel on the HX717, so they must be switching from A to B periodically while extruding to check for filament. I don’t plan to implement support for this as it would be VERY complicated in klipper to have a sensor that doesn’t report data on a regular interval.
The unknown pins on the connecter were the 3.3V supply for the filament sensor, the Fans tachometer and multiwire port.
Also it looks like fan power is direct wired and isolated, so if you swap the pins and use the 2 positive pins as negative pins and it should work, but I haven’t tried it.
```