After the due diligence investigation of my broken Monoprice Maker Ultimate (a rebadged Wanhao Duplicator 6) I determined my unit has indeed suffered the known common failure of the main 24V relay. I was also satisfied as to the cause of the failure – it was the consequence of engineering design decision I disagreed with, driving a relay far above its rated rating of 10 amps. But I was unsatisfied with the internet forum wisdom of bypassing the relay when it fails. I thought it had a useful purpose to serve and should be replaced instead of bypassed.
I ordered a replacement (or more accurately a pack of them, since it makes little sense to buy or sell a single unit of something so cheap) and got to work once they showed up. The first order of business was to get out the label machine and label all the wires connected to the control board so I know where everything plugged back in. The wires were held in place with dabs of hot glue to resist them from being shaken loose in transit, those globs had to be removed before I could disconnect the wires. After that’s done, the board came out easily.
Before I started de-soldering anything, I performed a quick verification test on the new relay: I connected 5V across the control pins and heard a reassuring “click”. Multi-meter confirmed that the continuity shifted from the NC (Normally Closed) to NO (Normally Open) pin as expected.
After that, it’s time to heat up the soldering iron. Normally I would label the old component “BAD” before starting on the project, to make sure I don’t de-solder a broken component and inadvertently soldered the bad item right back onto the board. (This is the voice of experience speaking.) But in this case, the melted hole is a pretty good way for me to tell which is the bad one.
It takes some effort to de-solder a component with 5 large pins like this relay, but nothing tricky. It just requires a lot of patience with the de-soldering tools at hand. And once done, the new relay soldered into place easily.
With this replacement, my 3D printer is back in action with all original functionality intact.