Thought I would share this for all of you out there with out of warranty Monoprice Maker Select V2 printers with dead Melzi control boards and who are thinking of converting to a different controller system. The following assumes a working knowledge of electronics construction projects and safety procedures. If you are unsure, don't open the chassis. There are potentially lethal voltages inside.
Step 1: Parts
To convert a Monoprice Maker Select V2 from original Melzi board to Ramps 1.4 board you will need the following:
A Ramps 1.4 kit (Longruner LK17) www.amazon.com/gp/product/B019TNELNU
Hot Bed Mosfet conversion board www.amazon.com/gp/product/B01HEQVQAK
SD card extension cable www.amazon.com/gp/product/B01HEQVQAK
SN-28B crimping tool www.amazon.com/gp/product/B01HEQVQAK
Dupont connector kit www.amazon.com/gp/product/B01HEQVQAK
wire ties, electronics hand tools, hex wrenches, voltmeter, etc.
Note; above parts and tools worked for me. Feel free to substitute although your results may vary.
Step 2: Instructions
Instructions for mechanical disassembly, reassembly and Dupont crimping instructions can be found here:
3D files for Matt's Ramps 1.4 mounting adapter bracket can be found here:
A customized Marlin firmware "configuration.h" file for the Maker Select V2 can be found here: https://www.thingiverse.com/groups/i3/forums/gene...
I'll let you find the wiring diagrams, Marlin firmware and the Arduino IDE firmware loader app on your own. The Internet is a better source than the CD that comes with the Longruner kit.
I'm using the Hot Bed Mosfet board because the Longruner Ramps mosfet, although 60A rated, does not have a heat sink and runs uncomfortably hot. There really is no room to add a decent heat sink, thus, the mosfet board solution. The SD card slot is on the side of the Longruner LCD display and inaccessible when mounted in the Monoprice chassis. I used an SD extension cable to get it out the back of the chassis and on top where it is easy to access.
Step 3: Install Notes
1) Unzip the Marlin firmware and rename the 'configuration.h' file to something else like 'configurationold.h' or better yet, move it to another directory. Put Mark's 'configuration.h' file in its place before uploading the firmware to the Mega board. Load the firmware to the Mega board using your PC before attaching the Ramps board.
2) Dupont crimps were a bit uncrimped at the wire insulation tangs and needed to be scrunched a bit with needle nose pliers to allow free insertion all the way into the Dupont connector shells. I replaced almost all of the Melzi connectors with Dupont except a few Melzis that went on clean with lots of room.
3) If you are comfortable working around open AC line voltage connections, test the whole thing before putting the boards into the chassis. I found I had to reverse one of the Z motor's leads (top connector when D8, etc. is on the left) and the extruder motor's E0 leads. Not sure if that was my fault or if the silk screening on the Ramps board is wrong. Also, you must connect 12VDC from the power supply to both sets of 12V ramps board input terminals as they feed separate board circuits. This is a good time to print out the adapter bracket as a test.
4) I used small wire ties, not screws, to attach the Ramps/Mega and the Mosfet boards to Matt's adapter bracket. It then attaches with 2 of the original Melzi board screws to the chassis. Spend some time to comb out the wires and detach, untangle and reattach as necessary to get the package right. There is not much space in there for the new system. I had to extend the mosfet board control wire to get it routed the way I wanted it.
5) I found the bed temp was pretty close when measured using a digital IR temp gun. I checked the filament feed calibration by putting a small wire tie 100mm up on the filament from the extruder entry tube and ran 100mm of filament through using the extruder controls in Marlin. It came up 8mm short so I am using 108 as a correction factor in my CURA slicing software. I'm getting good prints, a bit better, I think, than the Melzi board which failed after 2 years of use, although I think this conversion is only worth it if you have a dead Melzi or want to learn a bit more about how a 3D printing machine works.