Possible to convert the La Marzocco GS3 AV to MP?

Equipment doesn't work? Troubleshooting? If you're handy, members can help.
napierzaza

#1: Post by napierzaza »

I am looking to buy a GS3. I think my best situation would be to get a MP, but I seem to mostly see AV.

I wonder is it easily possible to upgrade from AV to MP? I imagine the grouphead is possibly much different to the point that it can't? Also maybe also the electronics as well too?

I also wonder about if older MP are possible to be upgraded to the new conical valve and strada modification? Or are you best to buy new in that case (if that is actually an option :? ).

cebseb

#2: Post by cebseb »

AV to MP is definitely possible, but extremely costly and not a simple matter. Better to spring for a brand new MP in the first place unless you manage to find an AV for around $2k.

Now going from the old MP to the new conical valve is a different story. From what I've been told by the La Marzocco techs, the retrofit is almost here. The price is still a mystery for the retrofit, however it will be far more affordable than the AV to MP conversion.

There is a third option of just doing the Strada Mod. That mod is widely available and reasonably priced (in my opinion). Hopefully the new conical retrofit is priced within reach. If not, then I see the Strada mod keeping its popularity.
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Peppersass
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#3: Post by Peppersass »

A quick look through the parts manual indicates that most of the cost would be in replacing the logic board and the group head components. Last I looked, the logic board is about $600. LM USA's online parts store has been down for days, so I can't tell you exactly how much the group parts would cost.

But instead of buying all those parts, you would buy the new retrofit kit when available, or the Strada Mod kit, plus any of the original group head parts not included in whichever kit you get (I think the paddle would be one such item.)

My guess is that you're probably looking at a total of $1,000-$1,500 for the logic board and group head parts.

In addition, three small parts are needed to close off the tube that leads to the flow meter in the AV (which would be removed) and a new fitting is needed to connected the boiler with the exhaust tube (because the 3-way valve is removed.) There's also a different fitting at the cold water input that feeds cold water to both the mixing valve and directly to the heat exchanger (which is fed from the flow meter in the AV.) Not clear if it was necessary for the MP's brew input water to bypass the mixing valve or if it was just that the fitting is simpler than the fitting that would be needed to reroute water from the tube that previously fed the flow meter. Finally, the button decals should be replaced because the MP and AV buttons have different functions. Again, I can't get the costs for these items until the LM USA parts site is back up, but I think it would be in the range of 10%-20% of the total.

Of course, before embarking on a project like this I would run the parts list and plan by the techs a LM USA. While I personally don't think the conversion would be all that difficult, I have eight years of experience modifying and repairing my GS/3 AV. Been inside the brain box and group head numerous time. If you're new to that sort of work, I wouldn't advise attempting the conversion.

If I hadn't already retrofitted my GS/3 AV with a variable-speed gear pump (cost was about $600) it's something I'd consider. Although my gear pump mod allows pressure profiling and long pre-infusion (with an upper limit of about 15 seconds), it can't control the flow as well as the latest version of the MP.

napierzaza

#4: Post by napierzaza »

Thank you so much for the depth of those details.
I would be interested and willing to do the modification. I've rebuilt an espresso machine before.

But looking at the costs it sounds like it would indeed have to be a very cheap AV purchase to make sense. I might tool around a bit more by contacting La Marzocco as you suggest. But I now at least have a range for how cheap I'd need to find an AV.

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AssafL

#5: Post by AssafL »

I don't think you need to replace the brain nor remove the AV sensor. It will no longer be useful as the paddle has a bypass - but the AV shouldn't interfere with the paddle action.

The 3d5 will continue running the 2 PID loops and safety timers.

May need to rethink how the paddle micro switch activates the pump, though.
Scraping away (slowly) at the tyranny of biases and dogma.

cebseb

#6: Post by cebseb »

The paddle micro switch placement is key. If you haven't yet, read through Peppersass's post history (especially his installation of the variable pump). I learned a lot from that member's (and a few others) contributions and it helped me convert my MP Mistral to Strada with little trouble.

That said, I'm very happy with my Strada mod. The new Conical Valve is very attractive with its full range of variability, however I've grown quite attached to the simplicity of 1 bar-3bar-9bar-3bar routine. I'll probably convert one of my groups to the conical and keep the other as is for now.
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Peppersass
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#7: Post by Peppersass »

AssafL wrote:I don't think you need to replace the brain nor remove the AV sensor. It will no longer be useful as the paddle has a bypass - but the AV shouldn't interfere with the paddle action.

The 3d5 will continue running the 2 PID loops and safety timers.

May need to rethink how the paddle micro switch activates the pump, though.
It might work to use the AV brain and leave the flow meter in place, but you'd probably want to leave the input water routing as-is (i.e., through the mixing valve and through the flow meter) instead of using the MP input fitting to bypass directly into the heat exchanger.

If you use the bypass fitting, the CPU will continuously report LOW FLOW. I think it'll continue to run the brew cycle, but my recollection is that it blinks on and off, taking over the display so you can't see the shot time. Even if it doesn't, the message would be very annoying. And I wonder if there might be a timeout on the brew cycle or the heater if there's no flow for a long time. I've certainly seen that message when choking the machine with too fine a grind, but have never let it continue for very long.

EDIT: I think it would work to leave the input water routing as is. I'm not sure, but I think when the MP valve restricts water to the puck, the flow is normal, so you won't get the LOW FLOW message. But the valve bypasses the excess water to the exhaust. Otherwise, you'd get those terrible banging noises when superheater water in the heat exhanger hits colder water in the boiler, as happens when I reduce the flow rate below 3 BAR on my GS/3 AV (low flow rate causes water in the heat exchanger to get too hot.)

I think the micro-switch is more of a problem. Probably would require modifying the front panel button board or the logic board to use the switch instead of the brew button. There are other ways to do it, but they would require both hitting the brew button and moving the paddle.

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AssafL

#8: Post by AssafL » replying to Peppersass »

You'd probably want to convert the switch to a pulse that would trigger the AV Function button on the way in - and trigger it again upon shutdown. A simple RC circuit may work - and if not - a small debounce circuit will do it.... I'd use the function as it isn't limited by the AV volume metric...

Also - If you do that change - keeping the lever to the right would mean you have an AV. You could pull shots with the regular AV circuit working. If you move the paddle to the left - it becomes an MP.
Scraping away (slowly) at the tyranny of biases and dogma.

napierzaza

#9: Post by napierzaza »

I can't seem to find anything in Peppersass' history.

But it is interesting. Gives me hope that if I can find even an old AV I might be able to make it work. Which seems doubtful anyways

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Peppersass
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#10: Post by Peppersass »

napierzaza wrote:I can't seem to find anything in Peppersass' history.
That would be because I've never found the time to do a comprehensive post on my gear pump mod! I've mentioned it many times, but haven't supplied the details. My bad. Maybe one of these days...

Very quick summary:

It's not a difficult mod if you've rebuilt an espresso machine and know your way around simple AC and DC circuits.

The minimum setup requires a 120VAC relay, a gear pump, a regulated 24VDC power supply, a potentiometer, a couple of resistors and a box to mount the pot. The cost should be well under $600, though that's based on the $500 I spent on the gear pump sample I bought from Fluid-o-Tech a number of years ago. The gear pump may be more or less expensive now, and might be available from other vendors (including LM USA -- which I still can't confirm because their parts store website is still down!)

The coil of the AC relay is connected to the GS/3 motor signal. This is easily tapped at a terminal block on the logic board. You disconnect the stock motor and connect the leads from the relay. It's that simple.

The gear pump motor is driven off the 24VDC supply. A separate 5VDC signal is used to regulate the speed -- 5V for max down through 0V for OFF. As I recall, the AC relay I used was DPDT and I used it to switch both voltages to the gear pump so there will be no voltage applied to the motor if the GS/3 is not in its brew cycle.

You can use a resistor divider to drop the 24V to 5V, which is then connected to the pot to adjust the speed voltage. My setup is a bit more elaborate: I built an interface box to which the gear pump, GS/3 motor signal, 24VDC supply and pot box connect. The relay is mounted in the interface box. I used a 5VDC voltage regulator to get the control signal voltage instead of a resistor divider. I added a four-position switch for Motor Off, Profile, Normal Speed (9 BAR) and High Speed (12 BAR). And fanciest of all, I added a circuit to make the metalized pot knob touch-sensitive. When I touch it, the circuit automatically goes into Profile mode, and when I let go it drops back to Normal Speed mode. That way, I don't have to remember to flip the switch before and after pulling a shot (this is a not a necessary thing, but I thought it would be cool to implement.) Oh, and my circuit contains an output signal from the motor to an external RPM display I built using an Auber counter. Totally unnecessary, but fun.

With the motor off, pre-infusion takes place at line pressure. I installed a high-quality Swagelok regulator with good flow rate to ensure a stable pressure that can go as low as 1-2 BAR to slow the pre-infusion. Such a low flow rate can cause the loud banging noises from superheated water that I referred to above. The solution is to run the steam boiler until it starts autofilling. The lower temperature in the steam boiler prevents water in the heat exchanger from overheating.

One caution: The bypass valve in the stock pump won't let the pressure go above 9 BAR (or whatever you set it to.) But my gear pump doesn't have a bypass valve and can develop pressure greater than the GS/3 limit of 12 BAR. Therefore the pot speed must be limited so it never exceeds 12 BAR when the GS/3 OPV is set according to instructions in the manual (12 BAR max when heating after a shot is pulled.) Although there is a version of my gear pump that does have a bypass valve, the manufacturer specifically states that it is only a safety device and must not be used to set pressure. Doing so will void the warranty. My guess is that it's not built for continuous duty.

Note that this limitation also makes it problematic to add a needle valve after the gear pump, ala Slayer -- an external bypass valve would be needed between the gear pump and the needle valve. I've always wondered if the Slayer has such a bypass valve. Does anyone know?

My project was made simpler by having outboarded the stock motor and pump a few years earlier (and that was made easier by buying an aftermarket motor instead of removing the GS/3 motor, which requires removal of both boilers.) So I had already tapped the GS/3 motor signal and installed a longer output water hose. All I had to do was build the gear pump circuitry, test it, remove the stock pump and motor, and slide in the gear pump.

If you don't mind drilling the chassis of the GS/3, I think there's enough room to mount the gear pump inside the GS/3 -- if you remove the stock pump. You could put the rest of the electronics in an external box, with just a single 4-wire cable running into the machine to the gear pump.

As I've said before, I'll try to post some photos at some point. The reason I've delayed is that I also want to post about how I outboarded the stock motor and pump, which affected how I did the gear pump mod.