Brewunit block

[jdk]

Hallo,

I have a Royal Professional (110V) that has required several small repairs.

The gear box had a broken tooth, which left the gears not in a home position.

With both gears replaced and set in home position, the unit still indicates "descale" and "brewunit blocked".

With the unit ON, there is no voltage at the red/black, brown/black wires that feed to the gearbox microswitches. I would expect there to be voltage in order for the machine to know it's in home position.

All other microswitches are getting voltage, otherwise they would generate LCD errors (dump box, etc).

I have translated several web pages (Andy's FAQ) and some posts here.

It would seem the voltage is blocked, either by a short, or an electronic component that has failed.

Any advice on how to step through this diagnosis would be appreciated. And I did see a post on a repair manual for the Royal Professional. It's OK if it's in German. Google translate is my friend.

Many thanks (Vielen Danke!) for the forum.

It's been a number of years since I've been to Germany visiting distant relatives. I sure miss it,
especially the Black Forest cake.

-J

 

[hmilbradt]

Hi,

Welcome in the Forum.

Open your System, pull the plug of the gear microswitches (JP1) and measure the voltages at the pins between red/black and brown/black. They are supposed to be at 5 VDC. This level indicates ... the microswitches are open. In the closed position the voltage level is pulled down to GND, in the open position the voltage is pulled up to 5 VDC by the resistors R4 and R5
The attachments show diagrams of the switches and the position of the parts involved on the board (within the red rectangles).

If your tests indicate everything is o.k, we have to tackle the 120 V power circuit of the gear motor.

regards
Harry

 

[jdk]

No voltage at JP1.

Upon further inspection, I found some solder resin burn on the M6AV1-8 board.
Specificially at the 0.68 Ohm 3W resistor (the medium size white one). The resistor has no resistance.

Rather than order just one resistor (I'll have to order on-line), I'd rather order a few electrical components. This based on some postings here. I am thinking power supply capacitors, known transistors that commonly fail, resistors, etc. Suggestions are welcome.

Thanks.

J

 

[hmilbradt]

Hi,

I would appreciate if you upload some sharp, high resolution pictures of your 120 VAC - M6AV1-8 board.
The 3 Watt 0,68 Ohm resistor, you mentioned, is part of the grinder circuit. On 230 VAC-boards (in Germany) a 1,5 Ohm resistor is used. The voltage drop across the resistor is measured by the microprocessor.
This PDF-File shows parts used on Saeco boards and replacements ----->>> Ersatztypen für Saeco-Halbleiter ---- Autor: hmilbradt und Saeco-Bastler

regards
Harry

 

[jdk]

No grinder circuit makes sense, as test mode did not see the grinder.

Thank you for the electrical component list.

I have uploaded the pictures to my album.

Links are below.

The pictures were resized based on the forum upload software. If there is an alternate location
to post the original sized pictures, let me know.

If you need any other pictures, just ask.

Large back of circuit board
http://www.saeco-support-forum.de/members/jdk-albums-m6av1-8-picture50-boardback.html

Close up of resin burn for the 0,68 resistor
http://www.saeco-support-forum.de/members/jdk-albums-m6av1-8-picture49-resinburn.html

Component view of board
http://www.saeco-support-forum.de/members/jdk-albums-m6av1-8-picture51-p1000101-1.html

Angle 1 view of component board
http://www.saeco-support-forum.de/members/jdk-albums-m6av1-8-picture52-p1000102-1.html

Angle 2 view of component board
http://www.saeco-support-forum.de/members/jdk-albums-m6av1-8-picture53-p1000103-1.html

J

 

[hmilbradt]

Hi jdk,

Thank you for the pictures.

regards
Harry

 

[jdk]

I did some more diagnosis.

I seperated the LCD/CPU board from the M6AV1-8 board to run some voltage tests.

I confirmed that the transistor (LM 2940CT-5.0) is producing 5 V output.

I suspect that this is the only 5V source, which is then fed to the LCD/CPU board.
If it's no the only 5V source, this may lead me to diagnosing the LCD/CPU board after
fixing the power board.

The two wires that feed the grinding motor at JP2 (brown and black on my machine), initially showed 22,6 volts. Now showing 5 volts. This seems incorrect to me if triacs are controlling the voltage.
I know some volt leakage will occur.

I did an ohm meter test on the triacs and transistor. Machine was off.

All triacs showed resistance, even as they are soldered on the board. Just a simple test
looking for obvious errors.

What I did find is the TIP33C transistor showed no resistance between the base and two other terminals.

So, this leaves my current test results with one bad resistor (0,68) and likely one bad TIP33C.

Thanks again.

 

[hmilbradt]

I confirmed that the transistor (LM 2940CT-5.0) is producing 5 V output.

Hi,

There ist only one voltage source for the 5 VDC. Its supply ist on the power board --->> ....... power supply on M6AV10 ... The voltage is fed to the CPU-board via connector JP14 -- pins 1+2.

regards
Harry