A couple of years ago I worked with a couple in northern Mexico to establish a nonprofit coffee shop for the international climbing community there. They've recently run up against an issue with their espresso machine that seems to beg for a simple diagnosis that I can't provide. Any help? They describe the problem and an attempted diagnosis this way:

The system:
Rancilio S20 Tecna DE from the 1990s (was discontinued in 1999) with an external pump feeding water from a five gallon water tank.

The problem:
...my group head on the right became synced to the hot water spout and vice versa. When the go button is hit for either hot water exits from both. The messed up group head is on the right, the group head on the left works like an ox.

Diagnosis from an amateur:
All important plugs were checked and cleaned, however no rust or corrosion were growing there. It doesn't seem to be electrical. I switched the five button control panels for each group head with the same problem and the same group head. So the user controls are not the problem.

Is this a brains issue? Can anyone help with maybe a procedure to narrow things down?

Thank you!

No experience with this machine or this problem, but based on other electronics knowledge...

Sounds like a classic short circuit.
Or could be the brain box. Hard to say. The 3way for the group and solenoid for the hot water are activating at the same time. It could be before or after the control signal. Without schematics or access to the machine, a diagnosis will be difficult.

I'd check the brain box circuit board and wiring for any crossed wires or corrosion.

(my armchair technician opinion)

In the event you didn't know this, the available docs for that machine are here:

http://www.rancilio.com/rancilio/downlo ... language=3

For sure it sounds like a control box issue and a call in to Rancilio might be beneficial after following Allon's helpful hints.

While certainly not a real fix, you can always defeat the hot water solenoid by unplugging one connection.

Using the wiring diagram for the Tecna DE, I'd look for a crossed connection between the white-yellow wire and the white-blue (for group 2) or white-red (for group 1). I don't know which would be wired as the right-hand group, but I'd guess group 2....

You guys are awesome. I'll make sure they see the replies to this thread and will report back. Thank you!

OK, word is the brains are gleaming, wires show no corrosion of any kind and each is in its own proper place. They mention, though, that there are signs of heavy scale buildup that they hadn't noticed before. Could this all caused by a gunked-up solenoid or an actual blockage? Is this extremely obvious?

It could simply be a stuck solenoid on that group. If it is like my two group, the brew button for either group kicks in the pump and opens the solenoid for the water supply to that group while the other group stays closed. One supply line for both groups with a solenoid that opens the brew path to that group. If one solenoid was stuck open, water would run from it whenever the pump kicks in.

Could this all caused by a gunked-up solenoid or an actual blockage?

That would be very, very, unlikely given your original (understandably, 2nd hand) description of the problem . . . because you said:

...my group head on the right became synced to the hot water spout and vice versa. When the go button is hit for either hot water exits from both. The messed up group head is on the right, the group head on the left works like an ox.

While it is possible that something is being "lost in the translation" and certainly it would be a good idea to rid the machine and/or some individual components of scale, I recommend you simply instruct them to electrically disconnect the hot water solenoid valve and find another source for hot water. This, at least, buys a little time until someone more knowledgeable about this particular machine (hopefully Rancilio) can provide a solution.

Thanks very much, Eric, Dave, and Allon! I got some updated details from the owners and it does appear that a call to Rancilio is in order, as the tricky grouphead is now firing on and off at random with no input from the user, and this with the hot water tap disabled. It appears that a solenoid is leaking onto the main power connection where it enters the machine causing some arcing (!!!). Allon, I think we found your short circuit. They have wisely unplugged the machine.

I know next to nothing about the electrical aspect of coffee machines, so I don't know how to test further along this line. I'm heading down there this weekend, so I can give some firsthand reporting later, and can make the call to Rancilio. This is definitely more than I know to chase down with my limited experience.

Many thanks for your continued attention!

A simple diagnostic test is to swap the wires from left and right grouphead solenoid and see if the problem switches over, too, or not. You might have to take some wire and crimp fasteners to make jumper wires.

"Ninety percent of all appliance problems are caused by bad contacts: switches, relays, and connections."
--The Maytag Repairman