It died on 10/15/10, and it took until tonight before it lived again in good health! Along the way, I developed a new appreciation for my moka and press pots, and a much better understanding of the inner workings of the machine. Thanks much to 5-year-old posts from 'DanLicks' for greatly reducing the learning curve (primarily here: http://coffeegeek.com/forums/espresso/machines/195800#195800
). While it was down, I took the opportunity to insulate boiler/pipes, descale, and replace the E61 gasket (which wasn't leaking, but was very dried out and came out in chunks). But that was the easy part...
The saga started here: Isomac Zaffiro - no heat
. Yes, that one. When you get to the punchline, it really should have been obvious. Look where that burned connector is...
Beginning there, I eventually discovered that I had the polarity reversed on the DC control connection to the relay. The controller isn't labeled but the SSR cares! Of course, with no labels it *looked* right. Fixed that and...
...it works, sort of. Heat in either mode, but not even hot enough to brew. Controller indicates 'heat on' when under temp, but heater isn't on for quite some time. No heat in steam mode either. Once it cools off awhile, it will heat in either mode. Something is stepping in ahead of the new brew temp control system and cutting power at a lower temp, and it has a huge deadband so takes forever to reset. Bad steam 'stat?
Sure enough...with a 50°C setpoint, the controller holds the boiler temp right there...not that you want to drink what results. Yank the steam 'stat out of the circuit completely, and with a 105°C setpoint the controller will hold the boiler in a rock-solid 104.5-106.5°C cycle (at the sensor). Water temp at the brewhead at the top of the cycle is ~94°C, but I haven't yet done formal temp checks over the course of the cycle.
As DanLicks said, this would seem to be an excellent alternative to a PID at ~50% of the cost. Total cost for the parts was ~$150, plus $20 to ship from Canada (Minco has a minimum order amount that this did not meet, so I had to buy from their only North American distributor, Mod-Tronic). The components are smaller and easy to place inside the machine using the existing tab for the original thermostat. I used the following parts (same as DL save the sensor, which either was a typo or has changed):
S17624PDZT40A: sensor ("40" is lead length in inches...could be way shorter, but this is all they had in stock)
I plan to fabricate some sort of external dial to adjust the controller setpoint, and ideally a display as well. The controller has a simple voltage output to show both setpoint and sensor temps (1.00V DC = 100°C), and I have already installed a pigtail to carry this to the outside of the machine. Anyone know where I can get a teensy 2-input (and 2-line?) panel voltmeter? The orange multimeter lying on top w/exposed wiring just isn't going to fly for very long with SWMBO. Of course I will also replace the steam 'stat.