Posted Sun Sep 16, 2012, 1:08pm Subject: Wega Mininova Rises from the Dead
So my Wega Mininova, given to me by a generous friend when he upgraded, went from having some quirky personality to just flat-out dead. Were it not that it made such excellent shots and decent cappuccino foam, I would've been very tempted to take the easy-way out and pick up a new machine, such as the Breville Dual Boiler. However, I just couldn't bring myself to junk a perfectly repairable machine, especially since the previous owner had upgraded the unit to a nice plumbed-in scroll pump.
I had figured out one quirk - the control board would shut down intermittently, disabling the heater and all controls. This turned out to be the low-voltage transformer that powers the board. After it heated up, the transformer would open and cut out power to the board. I replaced the PC-board mounted transformer with an external multi-tap doorbell transformer from Lowes. This has taps for different voltages and is encased in cadmium-plated steel, thus looking very at home bolted down low in the machine. We used the 16v tap, given the toasted board-mounted transformer was marked for 18v secondary. Less heat to waste in the voltage regulator in an already hot environment.
The second quirk - a sticky pressurestat was replaced with a quality three-pole unit that my friend had tossed in with the machine when he brought it over. This required fabricating an additional support bracket, and it worked out quite well. It has robust contacts and just looks like it will last and last.
The third quirk was a leaking vacuum-breaker valve on the top of the boiler. This I replaced along with new copper crush-washers.
And finally, the heating element was having occasional leakage to ground, tripping the GFCI the machine was plugged into. Replacing the heater afforded the chance to descale the boiler. Wow was it a mess. The Wega doesn't use the boiler water for anything other than the heat exchangers and steam generation off the top, so there is no regular way to purge out the water. Fortunately some descaling solution cleaned up both the inside and the outside where slow leaks from various fittings had built up calcium externally as well.
Fortunately, my mountain-fresh city water is very low in hardness (about 30 PPM CaCl, or less than 2 grains of hardness). I still plan on flushing the boiler regularly, as even that low level of hardness will still accumulate. One idea we had is to open the steam valve and let the scroll pump overfill the boiler from the bottom inlet with the level detector disconnected. This idea worked out well enough when we tried it, though the motor hit thermal overload after flushing about a gallon and shut down. While waiting for the motor to cool, I then drained the boiler through the side T fitting. We then let it refill back to the correct level, and only then reconnected the heater element.
It took my friend and me, both us of mechanically/electrically/coffee inclined, basically the entire day to repair the machine. In the end, it was worth it. Cappuccinos this morning made with fresh delivered whole milk, and Monkey Java blend from Sweet Maria's that I had roasted the day before in anticipation of having a functioning machine again. Pulled off two latte-art ferns as well.
Posted Sun Apr 21, 2013, 3:10pm Subject: Re: Wega Mininova Rises from the Dead
Thanks very much for trail-blazing this fix! I'm on my 3rd Giemme controller now. I ID'd the problem as a heat-damaged power supply, too, and relocated the circuit box outside the chassis to cooler climes. But, I haven't tried your repair yet, just looked for the same ps, didn't find it, and wondered if there was a more general work-around.
Now that you've done it, I'd love to see a snapshot or, better, a diagram of your mod. Wondering, does your Lowe's transformer have separate plug-in, or have you integrated it into the Wega's power? Assume you'd need to solder its ground & 16V to the same points as the original, failed transformer; did you remove the original one, or just leave it in place? Would you also please further identify the Lowe's transformer that you used?
This is a great machine, but the controller is definitely its weak point. It would be great to stop living in fear of ticking brain-death!
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