I'm less cranky now. The PID is very stable and it works fine. I have no issues with the idea of a wheel on a potentiometer either. Yes, a pot can drift a bit, but that's not all that big of a deal.

Of course, in talking with the La Marzocco people about my (extremely) sour shots, I got the lecture about technique. It is a fair question, but I've been consistently pulling good shots for years on the Anita. My technique may not win me the barrista of the year, but I'm pretty consistently rewarded with a decent tasting espresso most of the time. The sink gets one here and there, just like anyone else.

So the Linea Mini is working, within LM's spec. And I will (in lack of a scace) agree that it was calibrated.

There's a bit of a user-interface issue, which I think is at the heart of it and LM is making life hard on themselves because of it. Once they explained how the brew temperature is calibrated - then it all made (some kind of) sense.

So some stuff I've figured out. The PID thumbwheel has a printed scale on it. It covers 85c-105c, with each division on the dial represent 0.5c step and a number appears every 2c degrees. The US version of the dial, covers the same exact range with the same steps. They mark the ends with 185-221. The middle is marked 203 degrees. The rest of the numbers are marked with fractional numbers, which are the Fahrenheit conversions of the 2-degree markers. But that's how it works. There's a clicker mechanism that has about 9 clicks between each 2c degree marker.

So, on my machine, as it came out of the box looks like this:

Minimum setting rotation mechanical stop. Notice that the "185" mark is just under the metal at the right edge of the wheel.


Maximum setting rotation mechanical stop. Notice that the "221" mark is now just under the metal at the right edge of the wheel.



Note that the highest number and lowest number, align with the forward lower edge of the metal panel (right edge of the wheel).

It doesn't exactly make much sense, does it? Since the highest and lowest numbers align with the front edge, not the 6-o'clock position, one might assume that for some reason, that's the index point. On the other hand, the 6-o'clock index point, you get a lot of white space below 185 and you can't reach the 221 number at all.

Since there's nothing in the manual, where would you think the index point is? Maybe the knob wasn't put on right? Who knows, right?


So, what's the deal?

The trick is in the calibration process, which explains why on my unit, there's quite a lot of "white space" and it stops far short of the max number on the dial.

How it is calibrated - if you look inside the machine, you'll find:



So here's how they do it: No electronic calibration is possible on the controller, there's no trimmer pot or programming port. The pot is set to its mid-mechanical rotation point. The machine is allowed to come to temperature, and they use a scace device to measure the actual brewing temperature. Then they put on the dial sticker so that it aligns with the reading.

In this case, at mid-rotation of the pot, the machine produced an actual 198.3 degrees F brewing water temperature. The "12" means to offset the center of the dial sticker by 12-clicks of the clicker mechanism. So the middle of the scale is 203 on the sticker, but to get the number to line up with the actual reading, the sticker has to be offset +12 clicks.

Now, if you offset the sticker by +12 clicks, if you go to the lowest mechanical stop, you'll see whitespace at the 6-o'clock index. (just like my photo above). It will take exactly 12 clicks of positive rotation to bring the lowest number into view.

And here we go. Rotate the wheel to the mechanical low stop, then rotate exactly 12 clicks up and bing, there's 185f.

Now, on my particular machine, the PID adjusts from some temperature below 185 degrees F (whatever 12 clicks equates to) to something around 214F, where the pot stops turning. There's a lot of wheel rotation angle that's well below usable temperatures. There's a much smaller amount of rotation that's above usable temperature.

But - if you trust the 6-o'clock spot is right, and it seems to be, then everything starts to fall into place quite well.

At this point, I'm chalking it up to my misunderstanding, contributed to by the lack of manual information and the happenstance of placement that made it appear the index point was at the front corner of the knob slot, and not the 6-o'clock position.

I'll post more thoughts on this later. Have to stop now.

I figured it was a misaligned dial. Funny that they put on the sticker after calibrating the setting. It requires more finesse than to push the dial on after calibrating the pot (which is how I would do it).

Fortunately it's a simple problem to solve. The catch is that it's a pretty tight area to work in to remove the nut that holds the pot in place. But once you can unscrew it, you can pull the pot back and reseat the dial in the right position.



This is assuming of course, that the dial is not secured in place by a screw on the end (but from the above pic, I doubt it. You can probably peek up the side of of the case into the dial opening to find out). If it is, then it'll be a case-off job which will be a big hassle, and probably not worth the effort.


ps. just as a side note, my machine has no written calibration values on the frame.

Whatever you do, do NOT move the pot!!! Do not re-align the dial!!!

I figured it was a mis-aligned dial too. But in reality, it is SUPPOSED be that way. It may look misaligned, but that itself, *is* the calibration.

If you look on the bracket where the click mechanism is, you may find another hand-written note. There is on mine, a + and -, with a "12" on it near the plus side. It was hard to get a photo of.




The nice part is La Marzocco that is configuring the actual brew temperature, which is PID + any offset to the brew point. Kudos to LM on calibrating with the scace.

A note in the manual, or a slight change in the design of the dial, would make this perfect.