The Espresso Machine Restoration site
A non-commercial site for those interested in espresso equipment repair and restoration.
Volumetric dosing control & which La
Marzocco control unit do I have?
One of the most confusing issues concerning La Marzocco machines has been the upgrades in the past decade
to the Gicar control units.  And to make it even more confusing they have been given names rather than serial
numbers so you have no idea which is which.  

Anyway, wonder no more.  Here are the "brains" and keypads explained.
What are the components?

1. The Black box, aka "brain" aka main control unit.
2. The keypads, aka "button box".
3. Ribbon cables.

What do the components as a whole do?

The control units are what make a semi-automatic espresso machine an automatic semi-automatic machine.  
They allow the shots to be measured accurately by volume with the help of the flowmeters.  The shot is started by
the barista but the control unit will stop the shot automatically when the pre-defined volume of water has passed
through the

Besides controlling the shot volumes, the units also incorporate the
water level unit for the steam boilers and
the single boiler on a HX machine.  So besides controlling the pump and the 3 way solenoid valves attached to
each group they also control the pump and the solenoid that fills the steam boiler.   The water level unit probe is
obviously connected to the control unit.

To recap, the controller has two functions; to control the water level in the steam boiler and to control the
volume of water that determines the shot volume.
What's inside the black box?

The control unit is supplied by the 220V (or 110V) mains supply of the machine.  The control box then transforms
this 220V AC into 18V AC with the transformer on the circuit board.  This 18V AC is then converted to DC through
a series of diodes and finally a capacitor to filter out any remaining AC signal.

What is left is 18V DC which powers the board relays and flowmeters and 5V DC which powers the
microprocessor and logic circuits.

The unit's relays control the 220V AC for the pump and the 3 way solenoid valves for brewing operation.  They
also control the pump and another 3 way solenoid used for filling of the steam boiler.

So on an automatic semi-auto machine it controls everything?

Yes and No.  When you buy an AV La Marzocco machine you get the benefit of both the consistency and ease of
the volumetric dosing, but also the versatility and control of an EE machine.  In reality you get the AV controls with
a completely separate EE circuit in case of malfunction, i.e. if one of the keypads dies during morning rush-hour
then you can still override with the EE rocker switches. The only exception to this is if the water level control goes
belly-up and then you will need to replace the whole unit or get it repaired.   Even so you still have a manual fill
button on the steam boiler to get you through some troubling times.
What is linked to the black box?

                     Input side                                                                               Output side

220V input.                                                              220V control output to the group solenoid valves.
18V DC signal from the flowmeter(s)                       220V control output to the pump for brewing (group) operation.
A ground signal from the water level probe.            220V control output for the solenoid to fill the steam boiler.
A ribbon cable from the keypads/button boxes.       220V control output to the pump for steam boiler filling.
                                                                              18V DC output (to be switched) to the flowmeter.
Changes to La Marzocco control units over the years.

This is the confusing issue.  Certain changes have been made over the years to the control units.  Current
production units has the wizard 3D5 Units.  The now obsolete units are called Mask and Non-Mask.  The easy way
to identify which unit you have is by checking the ribbon cables and seeing how many wires it has - count the pins
on the connectors.

The table below  has a summary of the units.
What are the different button boxes?
Overheating issues

Because the control unit is placed so close to the boilers, overheating has been an issue on early machines.  
Sometime around the mid-1990's a cooling fan was introduced to suck in cooler air from outside the machine and
direct it onto the control unit.  

The other way to do it is to move the box to underneath the machine or install some sort of metallic heat shield.  
The fans do work and they solve the heat problem, but they do suck in a luck of dust!
This website is created by Paul Pratt, Hong Kong 2004. If you would like to use any of the images or text I am sure
I will say yes, but please ask first!  

Email me here.

Inside the black box.
A current spec button box.
The location of the control unit.
Ribbon cables link the button box and brain.
Flowmeters are linked to the brain.
unit name
Used in
3G Part
Number sample

Up to 1990
Square buttons.
5 red LED's
Internal key
8 Pin
Coloured ribbon
Square buttons
4 green brew LED's
1 Orange LED
External key
10 Pin
Grey ribbon
1995 onwards
5 Green LED's
Chronos keypad
an option.
Hold swirl
16 Pin
Grey Ribbon
Chronos keypad, right.
A current 3D5 button box.
The box on the left is what you will find on current spec. Lineas and FB70's.  It
has 5 LED's.  To program you must hold the continuos brew (far right button
with the red swirl) for about 5 seconds until all LED's flash.  Press the button you
want to program and again when you have reached you desired volume.
The box on the right is called a Chronos keypad.  You will note that on the right
hand side it has a display window and it has 2 brew buttons missing.

The display will show you the shot time.  I am not certain why these are not that
popular.  I heard a rumour that it encouraged baristas to think like robots and
discard shots that did not brew in a certain time window and increased wastage
regardless of how well (or bad) it pulled.

Note: your 3D5 brain must have the chronos function, you can't just swap the
keypads out.  You may be lucky, check first with your agent.
A dirty fan on a 2G Linea.