I was willing to stop at "good enough for now" on modifying my open-box Monoprice Maker Select because I needed printers up and running. In the process of designing and iterating Sawppy's 3D-printed components, I kept both printers busy pumping out prototypes to see how the designs in my mind survived the translation into real world pieces.

Sometimes there was enough work to keep printers busy around the clock, and this was too much stress for the control boards inside these affordable printers. It's an inevitable tradeoff between price tag and robustness. In the case of my Monoprice Maker Ultimate, the weakest point in the chain is the main motor relay that controls power going to all the motors (both stepper motors and fan motors) and heaters.

This relay has failed once before, and under the constant workload, another one has kicked the bucket. It has started failing intermittently which shows up as brief interruption in motor power. Since the electronics are not powered through this path, these brief interruptions ruined prints, making them look like the motor drive belt had skipped a few teeth when the reality was the motors stopping briefly as the electronics continued onwards.

Last time this happened, I kept trying to diagnose belt skipping. Wasting a lot of time looking over mechanical parts that were working well. This time I recognize the symptoms and pulled out the control board before the printer failed completely.

Since it wasn't completely burned out yet, the relay exterior didn't look bad - only a minor discoloration that might have gone overlooked if we didn't know exactly where to look.

Relay exterior discoloration

Cutting away the relay's blue enclosure exposed a familiar sight: the interior is fried.

D6 Second Failed Relay

It's always easier to do something the second time, but addressing my second fried relay is still time spent not working on the project itself.