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Hi friends, today we'll not work at a car
The coffee maker of my art director is not working anymore
When starting the maschine, the motor runs much too slow
and then we have the red alert
Before we'll start, an important warning
Inside the maschine we have hazard voltages and water, working in the maschine may be lethal. Please follow the instruction only, if you have the appropiate knowledge
Unplug before opening
Dismantling starts at the coffee reservoir
It has 2 Phillips No. 1 screws
The second one is here
The upper cover has 4 screws
Here is a Torx T10 screw
In the hole, quite deep is a Pozidrive No 1 screw. You'll need a long screwdriver
2 short Pozidrive No. 2 screws are here at the front
The second one is placed here
Pull the ***
Lift the cover at the rear side, then at the left side and remove it to the right
Remove the sealing ring
The whole engine can be separated from the case
It is fastened by this screw only
Remove the cable from the relief
For separating the engine unit, the cable must be loose and press the micro switch of the grounds container a little
Using a screw clamp it is easier to work at the engine block
This micro switch detects if the grounds container is in place
For operating the maschine without, we have to bridge it
Just use such a double male plug and some insulating tape
In the front is a second micro switch which opens when the brew group is in
The AMP plugs have a security, use a very small screw driver
Don't bridge the contacts, you must insulate them
The switch of the front door I close with tape
The motor and gearbox for the brew group is under this cover
Loosen all the screws around
Remove the cover
This is the motor of the brew group
Here is the worm gear unit and a second transmission
If you take care that all wheels are on the shaft, you may run it like this for a short test
It works in principle but much to slow
I'll measure the supply voltage of the motor
Best you'll use such clamps for the measurement
Here we see the problem. Instead some 30 V, I measure some 7 V only
The motor is supplied by a rectangular voltage
Using the cursors I find 50 Hz for the frequency
Let's check wherefrom the cables to the motor are coming
The red cable here seems to lead to this connection at the electronics
I check this with the ohmmeter
Okay the cable ends really at this connection
Before we'll loose something, it is better to close the gearbox
Screw first counterclockwise to find the thread in the plastic
After all screws are in their thread fasten them
Let's check, if the coil in the motor is okay by measuring the resistance
20 Ohm are little less when expected, but the value is still okay
The motor has a series resistor which becomes very hot, thus it's realized as additional heating in the boiler
Let's check the resistor. It should have some 130 Ohm
It is okay!
All indicates an error in the electronics
Before dismounting the electronics I write numbers on all the connections
I start counting here, 1,2,3 ... 12
Unplug the power switch and remove the control panel
The electronic is fastened by 2 screws, one here and the second here
Unplug all connectors
Better to push them a little with the screwdriver when just pulling at the cables
A possible cause could be a failing power transistor TIP 33C
I soldered 3 test cables to the transistor and we have a look with the scope
We find again the much to low voltage
It is the right component on the heat sink
At this model the bolts has a nut, but I have seen also Allen bolts having a thread in the heat sink
The heat sink has 2 big solding points
Remove the protective paint
I'll try to desolder the heat sink
Use some fresh tin, heat it up and draw it a little from the upper side
The same for the other side and the heat sink is out
Use a pump for removing the tin from the holes
Heat it, use the pump and the hole is free
This is the power transistor without the heat sink,
It has 3 pins
For desoldering use first a little fresh tin, then heat it up and use the pump
The 3 pins are practically free now
It is fixed still a little at the center pin
I'll check the TIP 33C with the multimeter
Google knows everything. I found the data of the transistor in the web
It is a silicon NPN power transistor
The pinout is here
The symbol we have here
We have a diode between collector and base
and a second diode between base and emitter
I'll check now each diode in reverse voltage polarity and in forward bias polarity
I have here the pin numbers for every measurement
The expected value for a good transistor in reverse polarity is an open circuit and in forward bias polarity I expect a current starting at a voltage of 500 mV
In addition I'll test the resistance between emitter and collector
The first diode transition is connected to the instrument
And we find our TIP 33C broken
because we find in reverse direction a breakdown voltage of 1 V instead of an open circuit
This would be okay, we find 500 mV in forward direction
We'll have a look on the other diode
I put the minus lead on the base and plus lead on the emitter and a again we find 1 V in reverse direction
In forward direction the 500 mV are okay
We test now emitter to collector and we find 100 mV and the same in the other direction
In conclusion, the TIP 33 C is failing
Here and here we have a connection in reverse direction and the reason is a connection between emitter and collector
Another reason for our failure could be this Zener diode which is responsible for the regulation of the transistor
For testing the Zener diode we have to two tests
I have to check the diode function in forward direction
and I have to check the Zener effect
The diode function I check with the multimeter
The open circuit in reverse direction is okay
I change the leads
The line at the diode indicates the minus pole for forward direction
The diode is okay, I find 657 mV
For a dynamic test of the Zener effect I use this homemade transformator, because I need at least a peak voltage of 33 V
Here we put the Zener diode, the supply has 38 V
What would happen now in case of a breakdown?
A high current would kill our diode, thus we need a resistor for limiting the current
I want to limit the current to 20 mA
Let's calculate the neccessary resistor by R = U / I = 40 V / 20 mA = 2 kOhm
This easy circuit I make on the fly
I measure the voltage at the diode
You see how the peaks of sinus are cut by the breakdown of the Zener diode
Using the cursors I measure the breakdown voltage with 33 V
Measuring over the resistor you see the breakdown very nicely
This Zener diode works like in the textbook
The new transistor came by mail
I repeat the transistor check to show you a good one
Base to collector shows in forward direction 500 mV
and an open circuit in reverse direction
Between emitter and collector must have an open circuit in both directions
and finally base to emitter in forward and in reverse direction. The new transistor is perfect
Now I'll mount all together, I put the transistor in the board
I use thermal paste, it reduces the thermal resistance to half
I mount the heat sink on the board. It has a strange angle at this model
Push the transistor in until the hole is aligned
I mount both bolts to get some stability
and the nut at the backside
I heat the pin and then I put the tin
At the heat sink you'll have to heat the pin quite long
After soldering, cut the pins
Either it will work now, or I have to continue searching failures
Before mounting the electronics I add the protection cover
Plug in the lower connectors, lateron the access will be limited
Bring the electronics in position
One screw here
the second screw here
The decisive moment
and green
Remove the bridges, I start with bridge for the power switch
When mounting the control panel, take care that *** for the potentiometer is in the right position
Plug in the panel
Check, if the hooks are snapped in
Plug in the cables of the power switch
Remove the bridge for the grounds container
one
and the other
Plug the cables to the micro switch
Plug in the cables of the micro switch of the brewer group
and remove the tape from the door switch
At a car it would be called wedding
The maschine comes back to its case
Put the plug thru the hole in the bottom
Put the maschine in the guides
Shake it a little and the machine finds it position
Fasten the unit with the long screw
Don't forget the gasket of the coffee container
Glue the gasket around the control panel
Mount the cover starting at the right front side
First screw counterclockwise to find the threads
Deep in the hole is a Phillips 1 screw, use a long magnetic bit
Press in the *** on the side
The short screws are from the front side
and the second screw is here
Attention the screws of the coffee container are different, the long on is at the rear
and the second one
Let's see, if it works
Switch it on
This is the crunch
The machine is warm, I press the button for coffee
I don't drink coffee, but my art director is happy now
That means we'll have also new automotive repair videos
Bye, bye. And the conclusion is: If you know to repair a Porsche, you may repair a Saeco, too �