Because I'm a Maker I like to repair my own stuff, which some times is a problem because they stay inoperative while I find some time to figure the strategy of depure the problem. Repairing something is usually simple and fun, but finding the cause of the problem can be tricky. This tutorial is for those that would like to make an adventure on repairing consumer equipments but think they don't have the skills and is too difficult.
The reasons to repair something
- To save money - not my favorite motive because I've to spend time to save money...
- No waste - The pos-World War II era developed an economy based on premature obsolescence, wast and mass production. And we know what that is doing to our beloved fragile planet.
- It's funny and we learn a lot!
The equipment to repair
On this case I needed to repair an Indesit WD105T washing machine from 2001!
When I started a washing program the machine started to work, loading water but immediately after that started putting the water out and the programming knob start to rotate and the LED start flashing without stoping.
Step 1: Opening the Machine and Test Components
Before open any electrical equipment be sure to unplug from main power supply. Make sure you are working according the safety rules to avoid any electrical accident. Inside all electric machines powered by main AC supply there are capacitors that maintain high voltage charge after unplugging the machine from main supply. Be careful on identifying this capacitors and make sure they are safely discharged before starting any your work.
Opening the machine and test components
After opening the machine, on the top and the back, I've tested all the electromechanical components, to verify if they where good.
The machine have different types of componentes:
- solenoid valves
- heating resistors
- resistive temperature sensores
- pressure switch
You can test all of this components just by measuring the resistance between terminals, using the ohmmeter function from a multimeter.
On my case all the components seemed to be good and the suspect falls on electronic controller board.
Step 2: Inspect the Electronic Board
The electronic board was easy to disassemble and inspect.
Immediately I observed that two tracks on the PCB where melted.
Good! I found the problem!
Bad! Something is burned :(
Then I follow the tracks and observed the components on the circuit and found a "black component" (TO-92 type of package) that was cracked.
The cause of the fail
This board worked for 12 years, but a design problem caused the fail. Two tracks were too close. The clearance between this two tracks wasn't enough and with humidity and because the solder mask of this PCB was of bad quality, a surge current caused a short circuit on a weak spot. The surge caused the two tracks to melt and caused the "black component" to conduct very high current that cause the component to heat very fast and explode!
However the designer of this circuit include a special component, called MOV (Metal-oxide Varistor) that absorbed the energy of the surge current and avoid that the components of the circuit burn, specially the IC's that are more sensitive than other discreet components and more difficult to find a replacement.
Step 3: Identify the Burned Component and Testing
Usually a component incapsulated on TO-92 casing is a transistor, but on this case after a close look on other similar components on the board I found this reference: Z0607
After googling "Z0607 data sheet" I found this pdf.
How to test a Triac?
Testing a resistor is easy. You only have to use the ohmmeter function of your multimeter to read the value and confirm if is according the color coding stripes of the component, but testing a "black component" is much more difficult, right?
No. Can be very easy. On this case I had the luck of knowing the component reference and found the data sheet with pinout.
Testing a Triac is simple. You just need to follow this steps.
Step 4: Repairing the Electronic Board
I was very lucky and didn't have to spend a dime on the repair :)
The circuit that burned was an output signal and apparently I only have to replace the explode Triac, but I realized that this board had 6 similar output circuits and one of them was not being used. This was pure luck since I saw that the connector was missing some wires. One output circuit was not being used on this machine model!
On the first figure you can see, inside the red boxes, the components of one output channel. From the top, you have a jumper from the IC digital output. Then theres a couple of polarization resistors, that are connected to the gate of the Triac. The blue component is a MOV (Metal-oxide Varistor) in parallel with T1 and T2 pins of Triac.
On the second figure you can see that I've desoldered one jumper and cross connected the next one to use the output Triac circuit that was not need used. After that I switch wires on the connector to the washing machine.
And thats it! I've sprayed the soldering points with isolating varnish spray. Connected everything, cross fingers and power up the machine and it did work!
This was how I've repaired the electronic controller of my washing machine without spending a nickel :)
Step 5: The Tools You Need
You don't need many tools to make this kind of repair.
- Digital Multimeter (I still use my first digital multimeter, a Kiotto KT-1990CX with 25 years!)
- Soldering Iron
- Isolating varnish