La San Marco - premature stopping

[CabinCoffeeBemidji]

Hi! New to the forum here - hopefully I can glean some expert advice I recently opened a second coffeehouse/bakery in my area of the world. I installed a very retro La San Marco 85-16M (group 3) and have been experiencing a very unfortunate issue. The right most group does not appear to be affected, however, both the middle and far left will frequently stop pulling shots, prematurely. I don't think it is a calibration issue, because I have re-calibrated the volume dispensed multiple times. Plus each time that the issue occurs, it also activates a flashing light over the single shot ristretto button. I have contacted the area "espresso guys" (ESI) and that has only revealed how little they know about this machine. Anyone familiar with La San Marco that can shed some light on this problem? Thanks!

[noidle22]

I had the two group variant of this machine at my shop a few months ago and the coil for one of the group solenoids was low resistance and blowing the fuse.

Yours obviously doesn't have this exact problem but if the coil is not remaining energised whilst pulling the shot the valve will close and stop the shot.
You would see the usual pressure release from the valve drain if this is the case. Do you notice this? Or does it just stop extracting with no release of pressure?

Easiest thing to do to see if this is the problem is to swap the coil from the group that works across to one of the others and run a shot and see what happens.

If there's no luck, I would suspect a premature cut to the solenoids still but it may be the fault of the control board.

A way to check this would be to activate the semi auto switches on the left hand side of the machine. This will bypass the volumetric system and just run the shot as long as the relevant group switch is on.
If the groups work properly using this method then it's a volumetric system fault which is managed by the main control board.

You would hope this isn't the problem as it wouldn't be fun to try and fix.

Give these a try and see what happens. Try the switches first as it doesn't involve removing parts.

[noidle22]

Also, now that I've considered the blinking light problem, it may be the flowmeters not working properly. This could explain the error light that you are seeing.

Check them for any scale buildup and proper impeller rotation. You could also try swapping the wiring from the working group's flowmeter onto one of the others and see if the fault follows this.

[CabinCoffeeBemidji]

Forgot to jump in here to say thanks noidle22! I was going to start with the first recommendation, and upon opening up the machine I took notice that there were a few wires that had been neglected. I did make a quick swap of the components between the 2nd and 3rd groups (to test if the part was bad). I hooked everything up (wires and all) and all groups have worked great since. I believe there was a premature cut to the solenoid due to the fact that the they weren't even wired up correctly before