Solis SL-90 Adjustable Brew Temperature

Happy    This mod really works.
   I've been enjoying Black Cat at around 198F.

   Thanks for documenting.

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Panel As delivered, the brew temperature is around 185 5F. A bit low at the hottest. 'Ready' indication has far too much hysteris for repeatable shot temperatures. It's possible to add adjustable, and very repeatable, brew temperature modification to the Solis SL-90.

The pot allows the user to adjust the temperature above 200F. The LED indicates the heater element is ON. When it goes out, the boiler is at the set temperature.

These mods are not difficult. IF you've never soldered a PCB or wired anything, try to find a friend who has. PLEASE!
Open Take care removing the cup tray. Slide it forward just enough!!

Remove the reservoir. Remove the #1 Phillips screw at the bottom of the reservoir 'lock well' at the back of the cup tray. To remove the cup tray, hold the machine against your chest and gently slide the cup tray forward. Don't go more than 1/2' or you will break off the front panel tabs. Lift the cup tray and lay over the back of the machine on a pile of books. Optionally, disconnect the ground lug and heater connector to completely remove the cup tray.
CutStrapPCB If your relay PCB looks like this, STOP!!

These modifications are not for this PCB. They may work, but have not been tested. Proceed with caution. The PCB number is the same and the modification by the green wires matches the tested PCB. Carefully compare the PCB to this image. If the traces match, proceed. If not, STOP!
Part Parts List
15k 1/2w flame proof resistor. (30k: ——[ | | |    | ]—— for 220v machines)
T1 LED. Color Optional. The LED is ON when the element is heating.
1N4007 1A 1000V diode. [The 1000V is IMPORTANT!!]
500k LINEAR 1/2in pot and Knob to fit pot shaft
Hookup wire in 2 colors. 105C 20ga is fine.
1/8 heat shrink
Optional: Heat sink compound to replace the dried out compound around the sensor and over temp breaker.
Tools Required
#1 Phillips
Soldering Iron
Wire Cutter / Stripper
Heat Gun
Electric Drill
1/8in drill 1/4 or ?? drill for pot mounting boss. Optionally a rat tail file to enlarge hole from 1/4in
Hacksaw to shorten pot shaft, if necessary.
LEDAssy Trim the leads on the LED to about 3/8in. Trim the resistor and diode leads to similar lengths. Note that one side of the LED has a FLAT. This is the DIODE side. Assemble the parts as shown and solder the leads. Note that the BAND on the diode is AWAY from the LED on the FLAT terminal.
Take care to make good connections and don't take too long as you can destroy the LED and diode with too much heat.
LEDWire Connect about 9in of wire to the resistor and diodes and solder.
NOTE the FLAT on the LED and BAND on the diode.
LEDInsul Insulate the resistor and diodes with heat shrink.
LEDWires Twist the wire leads, taking care not to strain the LED terminals.
Resistor Desolder the top end of the ballast resitor from the PCB.
The resistor is the blue thingy in the middle of the photo.
Resistor Desolder the upper end of the resistor from the pad marked in the photo.
PotPrep Form the pot terminals to connect pins 2 & 3. Connecting pins 2 & 3 prevents an open circuit should the pot wiper fail. At low temperatures, ~50F, an open circuit in the ballast resistor prevents the SL-90 from starting.
PotWired Connect a 6in wire to each of the terminals as shown. Insulate with heat shrink. Twist the leads.
PotConnect Connect the colored pot lead to the pad desoldered above.
Solder the black lead to the free end of the resistor and insulate with heat shrink.
[The RED lead is the WHITE lead in the photo above.]
LEDConnect Connect the LED to the pads shown. Polarity does not matter as A/C current drives the heating element. See close-ups below for details.
LEDConnect1 Close ups of left LED connections above
LEDConnect2 Close ups of right LED connection above
Clamp The thermal compound from the factory dries out, reducing the thermal coupling between the sensor and the boiler, affecting boiler temperature control. Remove the clamp holding the sensor and the over temp breaker. CAREFULLY clean the old compound from the sensor and breaker. Apply new compound and replace the clamp.
Ensure that you replace the thermal fuse properly under the clamp.

All that remains is to drill the holes and mount the pot.

Range of Adjustment
Note : these temperatures are taken on free flow, so only the maximums are relevant.
With reduced flow of an actual shot, temperature variation is much lower.

If you just want to see when the boiler is at temperature, do the LED mod alone.

A simple way to raise the brew temperature is just desolder one end of the resistor and adjust the trim pot.
This method can render the machine inoperable at cooler temperatures.
With the resistor removed, the SL-90 interprets the readings as a frozen boiler.

Contact : ieales _AT_ ielogical _DOT_ com