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Oh RAMPS!

A RAMPS 1.4 board viewed from the top

The RepRap Arduino Mega Pololu Shield (RAMPS) 1.4 Remains one the most popular low-cost 3D printer controller boards. I had bought an entire kit recently from Amazon for 39.99 USD, which contained the RAMPs 1.4, a RepRapDiscount Full Graphics LCD, clone A4988 drivers (with 0.100 ohm current sense resistors), and a clone Arduino Mega 2650.

I’ve been planning to build an MPCNC Primo for a long time. After brushing up on some of my woodworking skills to make a table, it was finally time to get to the nitty gritty and start sourcing and building the Primo itself. I had a tight budget and needed fast shipping so I chose the RAMPS 1.4 kit.

The Build

RAMPS 1.4, displays, and stepper motors laid out on a messy table

Assembly of the kit was relatively straightforward. The kit came with 18 jumpers, though only 15 were needed to set the micro-stepping for the A4988 drivers to the appropriate level ( by populating all the jumper locations). Some headers were bent out of shape, but bending them back by hand worked well.

I power it on… and no display.

The Problems and Fixes

So through the serial monitor, I can tell that the Arduino Mega is still functional. Flashing Marlin gives me the Marlin prompt, good. Something else is preventing the display from powering on. I measure the voltage across 5V and GND on the Arduino: 4.5V. The regulator on this cheap Mega 2560 clone is far too weak.

The backside of the RAMPS 1.4, the Arduino Mega 2560: it has a LM2805 soldered to the back of it

To try to solve this, I de-soldered the power section of the Mega to prevent any sort of interfering with my new solution, and then stuck an LM7805 across the VIN and 5V lanes on the Mega. Not the best or most elegant solution, but it works for now. 5 volts!

Still no display…

The LCD controller adapter board on the RAMPS 1.4, with bypass wires

Using the pinout diagram on the RepRap wiki, I did some continuity testing for the “Smart Adapter” board. Turns out 5V and GND weren’t connected to the display connectors. I soldered in some wires to bypass the PCB, and voila! Backlight and display!

The RAMPS 1.4 with the polumer fuses removed, replaced with wire leads

The polymer fuses on this revision of the RAMPS are infamously bad. They have a tendency to randomly trip, and fail to trip when they’re sorely needed. Because I’m not going to run the RAMPS with heaters, I’m not running a 3D printer, “just” a CNC machine, so most the electrical risk is gone here. So I’ve decided to just de-solder the polymer fuses to avoid any problems with them, and I’ve replaced them with diode leads. Will these lead survive 5 amps of stepper current? I’ll have to see. I might need to add some more solder.

Don’t worry, when I build the enclosure I’m planning to add some automotive fuses to the power switch.