I began this rebuild about four weeks ago in Feb 2011. A friend of mine had an old Formula/Wega Mini (which later became the Mini Nova line) in his party barn in central Texas. He had to move and told his friends everything in the barn was up for grabs. And so this little beast became mine:



Almost all of the parts seem to be present, if sad looking. This appears to be a straight-forward single boiler HX machine.





Going into this project I knew I liked espresso, and that was about the extent of my knowledge on the subject. After digging around on the internets and finding various resources, such as HomeBarista I've pretty much learned what I need know to at least get started. And so the disassembly began.

One of the first things I noticed was the giant crack in the side of the pump.


Everything came apart with relative ease and went into a large citric acid bath. I brewed up about 3 gallons of hot water and dumped in about half a pound of powder. I chose this solution ratio mostly because it just seemed right... Parts came out looking very nice.



I was really very hesitant about the likelihood of getting this thing to ever brew again, until those first parts came out of the acid bath. Wow!! Golden pink is my new favorite color. Of all these newly beautiful parts my favorite is the pressure gauge. It doesn't have any numbers but it is in measuring pressure in bar. I'm very pleased that I was able to scrub this part clean again.




Dig the before on the frame:



This frame is powder-coated however it had a lot of rust hiding under the coat. I filed all these obvious rust pockets out and bead blasted those areas clean. However wherever the powder coating was undisturbed the bead blasting was very slow. There was no chance I was going to completely strips this thing clean, but I did get all the rust of, and I think it looks pretty good myself.





Another problem that became obvious was that the diaphragm on the pressure-stat is clearly busted.



However, this part can be rebuilt with the diaphragm kit for $30, or straight replaced for ~$55. I don't really know which route I'm going to go at this point. Before I address this problem I am going to re-assemble everything and simply close the circuit going through the P-Stat hand to verify that everything else is working. This has been discussed here: I need a Sirai P302-6 Rebuild kit

Wire harness, fortunately when I got this machine it powered up and the light turned on and no magic smoke came out of the control box. I'm really hoping that this box doesn't need replacing, however this nasty wiring harness has got to go.



I have checked the 3-way (brew) solenoid as well as the fill solenoid and they both work. The heating element measured 10 ohms or something like that. I don't remember what it was but it seemed right. That is pretty much where I'm at. I pressure tested the boiler and discovered a leak on the lower fitting of the HX. This has been mended, and everything is ready to go. I've got everything apart and cleaned, I've got my new pump in place and am going to begin reassembling. I'm going to try to replace every o-ring and crush-washer I find as I go. I have a feeling there will be a lot of tightening, running, leaking, removing and re-tightening in my future.

I figure my first move is to just test the new pump. It turns out there is a 1N4007 diode which appears to be wired in series in the pump connector. This diode measure open circuit both ways and is going to be replaced.

Does anyone have any advice in terms of which parts I should put together first for a sort of bare-bones pressure test and sanity check? If so please let me know. In the meantime I'll keep y'all posted.

JD

I'm going to lead with questions so the casual reader doesn't have to deal with the whole story. Please do read the whole thing if you are so inclined, whether you know how to help me or not.

Does anyone know why the control box would not engage the heater except if:
1) The P-stat had disconnected it
2) The tank was empty.
3) The switch is off.

Which brings me to my next question, how does the tank level sensor work? When the tank was full it was reading about 5 VAC, 0 VDC. All it is is a lead that sits in the boiler. What should it read when the tank is full, and what about when it's empty?

Here's the long version:
I finished cleaning all the parts as best I could, got my hands on some brass crush washers and an O-ring kit and took to putting this beast back together. Fortunately, every fitting and pipe seems to be a unique shape so it all went back the way I found it without having to refer to the pictures I took before I started disassembling everything. Not too many times anyway.

I got the whole thing plumbed up except for the P-Stat, which I know needs to be rebuilt or replaced. I plugged its port by hose-clamping a ball bearing into a small piece of tube and clamping that onto the fitting where the boiler leads to the p-stat.



For brevity (I was getting anxious to see this thing in action, and my friend who as helping had to go) I re-attached the old wire harness. I closed the circuit running through the p-stat, plugged it in and fired it up.

There are two switches on this machine, the left (Power) just connects AC line and Neutral. The right (Brew) connects two other things, the three-way solenoid in the brew group and something else which I can't remember. As soon as I threw the power switch the fill solenoid actuates, but nothing else seems to happen. The tank was empty, so I was surprised the pump didn't engage.

After a brief moment of tension, I threw the brew switch. At that point the pump it did engage, the boiler took on about half a liter of water then cold water began to flow from where the PF fits onto the group. I took this to be mostly good signs.

What did not happen was the heating element activation. I double checked all the wiring then followed 115VAC from the heating element across the relief switch all the way back to the black wire on the control box. For whatever reason the box decided not to close the circuit on that lead so the heater wasn't coming on. I finished the new wire harness just to be sure I didn't have a bad connection somewhere else and re-started the machine but got the same results.

For grins, and because I felt sure that there was water in the tank, I closed the circuit on the heating element by connecting the black return wire to gnd. It was drawing about 10 Amps AC and things started to get interesting. I could hear water boiling, my anti-siphon fitting started spewing steam until I pulled the little plunger up by hand (by tool actually). I found a number of leaks (which I was expecting) and I got the pressure gauge to show more than zero. And finally I got the brew group nice and hot and got water from the water wand.




Then something really funny happened, I disconnected my heating element work-around wire and the control box held the circuit closed. It was like the box wanted to make sure it was OK to engage the heater, and once it saw me do it, it figured it could too. Mind, I still had the p-stat hard-wired to allow heating.

I powered everything down, then powered up again, but this time the control box did not want to engage the heater, so I did it myself again then released it after while, but the box wouldn't play along this time. Weird.

Perhaps there's a flaky component in the control box, my background is in electronics so of this whole project the guts of the box are the only thing I am confident I can reverse engineer and fix. But I have a hunch the box is fine and some other component is sending flaky signals. Please help if you can, or even offers of encouragement are welcome.

JD

Looks like it's coming along.You're putting alot of hard work into that machine,good for you.Did you get those other things figured out yet?

Jitterbug,

Thanks, there has been a lot of part-scrubbing and wrench turning thus far, but it has been very rewarding. It will be even more so when I pull that first shot.

My friend and I took apart the control box and discovered a blown trace and a flaky relay. I'm not sure if these were causing my symptoms but they're being fixed anyway. I snooped around and confirmed that the boiler level sensor just uses water in the tank to close the circuit to ground. Here is my current approach:

Finish repairing and reverse engineering the Cubic Recirca Control box. Then use that info to figure out if any other parts are misbehaving. Here is what I think should happen, please correct any mistakes:

1) Power switch is thrown and power is applied to control box.
2) If the water level switch is Open (indicating low water level), the fill solenoid actuates and the pump begins pumping water into the boiler until the water level switch closes.
3) Once the water is at a safe level and the P-Stat is closed the heater engages.
4) The heater continues to run until the p-Stat opens

5) You get a jones for espresso, setup the PF, and throw the brew switch
6) The 3-way brew solenoid engages to allow water into the portafilter
7) The fill solenoid engages and the pump engages to re-fill the water lost to brewing

If any of these are false assumptions please let me know.

How goes the rebuild. I just started down the same road. I have the same machine, with a bust boiler and have started stripping it down. might see about brazing my boiler...or buy a new one...but that is painful.

Anyway, good luck.

Dave

Dr Chill, What an undertaking, that machine looks like new! Mine must be a little newer. I bought mine back in 2000. Most of the problems I've had were the control box. I have replaced it about every 2 years. I have kept them all in case i ever found someone who could repair them. I know very little about electronics.
Right now I have a valve issue, I think it's the 3 way valve and am ordering a new one.
But I'm not sure if you have yours running now or not but it does produce good consistent espresso. I'm sure you'll be glad you put the effort into it. Have you priced the new ones?