This alarm occurs in PR phase(process).The  Internal sterilization chamber temp.

< 134°C / 121°C the steam temperature reading  (internal chamber temperature probe) is below the minimum threshold.

Generally the main CPU board detect the alarm, thanks to evolutiv software and sensors.

This is the description of the alarm. But three conditions that cause it:

1/ Internal chamber temperature probe damaged

2/ Steam leak

3/ Steam generator heating element damaged

The first steep is tracking down the problem by elimination.

The internal Pt sensor is working fine

Remine to check for any leakage.

Door gasket:  I clean the chamber face side and door seal; run a sterilization cycle but the action did not remove the alarm.

To detect the possible internal leackage  we must run a vacuum test. If the test is negative and the alarm 390 occur, that means an electrovalve, a pipe or steam generator damaged.

Effectively, the alarm 390 occurs during the vacuum test, but to determine what component is fault, we must run multi different tests as follows:

1rst test:

Valves EVA/B/C:


o Access the components test sub-menu and power EVA, EVB,

and EVC

Listen for an audible click when checking and unchecking

the valves to ensure they are switching properly

o Check if there is steam leaking towards the condenser at any of

the three valves EVA/B/C

drop the condenser flat on the table, initiate a sterilization

cycle, and touch the tube that runs from the EVA/B/C assembly

to the condenser during the PPH phase of the cycle – if the

tube gets very hot during that phase it might indicate a leakage

at any of the three valves; clean or replace valve(s) if necessary.

The result no leackage

2nd test:

Vacuum alarm troubleshooting flow-chart

If…….A390………testB (checks for leaks on:

o 1-way valve (ULKA valve))

This one way valve is working fine, so I proced to testD.

testD checks for leaks on:

o steam generator


This test checks if there is a leakage at the one-way valve placed between the water pump and

the steam generator, also called ULKA valve.


o chamber interface

o valves EVA/B/C external


The 3 valves EVA/B/C are already tested good, the chamber interface is ok too..

The cause is a small crack in the steam generator.


The last testE is not necessary.



Bougrine-Professional Electronic Repairer From Morocco field:Dental Chairs & Stools , handpieces , micromotors etc.. dental supply equipments: Sterilizers,

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