TideLog Archive for the “Home Appliance Repair” Category

Hoover washer dryers used to be synonymous with quality and could go 10 years plus without issues, but now they just seem to be dropping dead left right and centre when really young. In the space of one day today I’ve both had a Hoover engineer come out to my parent’s machine, for a motor replacement under Hoover warranty, and later that day I myself was called out to fix another Hoover washer dryer, both the same model, different faults.

WDYN856DG

The patient was a 2 year old WDYN856 DG washer/dryer, with no signs of life, except clicking noises, following a loud bang during a dry cycle. Clicking relays are usually always main control unit failure, so myself and Martin, my repair assistant, got to work. There was no other life from the programme selector dial, LED segment display unit, buttons, or their LED’s, apart from the clicking. We pulled the control unit out, it looked fine from within its casing, but once unclipped from it, we saw the catastrophic damage:

Hoover-WDYN856DG-control-unit-PCB-in-shieldHoover-WDYN856DG-control-unit-PCB

Can you guess where the actual brain of that massive washing machine is? Nope, none of the big components! That tiny chip that I’ve circled in red is the computer of the machine, smaller than a two-pence piece! The rest of the board is just power regulation, the control relays, and the outputs for the motor and element, plus all the connectors for sensors. The two small plugs on the very right-middle are the programming headers for programming the EEPROM. You can see the giant ferrite inductor coil, and those big heatsinks? That’s the transistor & Triac that control the motor speed, they act as an inverter and tacho control. The higher the switching frequency of those transistors, the faster the motor spins. They get mad hot, and very stressed, especially the massive transistor to the right of the coil.

Unfortunately, as you can see from the picture, around where the microcontroller is, that is where the failure has occurred. The area is all burnt, and has catastrophically shorted. The yellow highlight on the left is also where some damage to a diode, resistor and capacitor has occurred. The damage is actually worse than it looks in the picture.

We had to replace the motor, and the front-end option selection button unit as they were unresponsive even with a new control unit. We can’t be sure of the exact cause, but we suspect the motor has shorted, and as it’s directly wired to the transistors, has caused a massive short circuit, taking out the control unit and the option selection button unit (which itself had microcontrollers on it, but these were visually undamaged).

Unfortunately you can’t just buy a new control unit and connect it up, the EEPROM needs to be programmed with machine specific code, the machine will just flash an EEPROM communication error otherwise. We had the Hoover engineer programmer, so were OK 😉

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Electric showers are great, but they do go wrong occasionally. At Kitamura we repair all types of showers. A lot of people seem to confuse “power showers” with “electric showers”. They aren’t the same. An electric shower simply heats the water, the water goes through the shower under simple water pressure itself. That is where power showers differ. They still heat the water, but they also have a motor assisted water pump, which acts like the turbocharger in an engine, where a little amount of pressure is converted into massive pressure by an impeller.

We recently got called out to a faulty Mira Essentials electric shower. These were made in 2000, and this one was suffering from random pressure drops, and weak output. Here’s a shot of under its cover, I’ve labelled its parts which I’ll explain below:

Electric-Shower-Components

A. Water input w/filter

The cold water input, with filter. This is a gauze filter that filters any silt in the water. If not filtered out it could collect in the water heater, and cause failure, or blockage in other parts of the shower system.

B. Water impeller.

This is not electrically assisted as in a power shower, but it helps to keep the shower running if there is momentary pressure drop due to something else being used in the water system like a tap.

C. Power and Temperature knob with flow solenoid

This is the ON/LOW/MED/HIGH selector, which works in tandem with two microswitches, and two heating elements. When the shower is switched on, the electric flow solenoid opens, allowing water flow. In the LOW position the water heater is fully switched off, and the water is cold as all microswitches are open. In the MED position, one microswitch is closed, so one of the elements is active, and in HIGH both switches are closed, making the heater operate at full wattage, in this case 4.2kw.

D. HIGH microswitch

This is the microswitch that operates the second element by turning the temp knob to HIGH as above.

E. Temperature knob.

This works by varying the amount of water that gets through to the output. By reducing the speed of water flowing through the heater, it makes the water hotter, and increasing it makes it colder. If the Mode selector is HIGH and the Temp knob turned all the way to HOT, the heater would be shut off by the TCO (Thermal CutOut) on the heater as the water temperature is too high, which will cause scalding to the person using it, and also damage to the heater.

F. Neon indicator PCB

This board contains the neon indicators for Power, Overheat, and Low Pressure. It also contains resistors to prevent premature wear of the neon bulbs, they are run from 240v and don’t last long, especially the POWER indicator, as that is on as long as the mains is on.

G. Mains input terminal block

Self explanatory, this is where the mains is wired in to the shower. In this case the shower had its own switch and fuse in the consumer unit, so we didn’t have to turn the electricity off to the customer’s entire house while we worked!

H. Water heater with TCO (Thermal Cut Out)

Here’s where the water is heated before going to the shower head. The two elements are individually controlled by the microswitches previously mentioned in C, controlled by the MODE knob. The heater contains a thermal cutout so that the elements are turned off if the water gets too hot. Once the water reaches a certain colder temperature, the thermal cutout switch turns the elements back on.

The thermal cutout is normally only activated if the temperature knob is on HIGH, and the TEMP knob set to its hottest, which is minimal water flow, as mentioned in E.

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In this article I’m going to help you diagnose and identify control problems in your washing machine. Modern washing machines all contain a computerized timer and control system, this is responsible for controlling all the different circuits in the machine such as the sensor network, motor, drainage circuit and the heating circuit. The main thing to remember, whether diagnosing a modern sensor washer, or a car electrical network, is that computers run off the same basic principle. Inputs and outputs, if a computer can’t get a reading or signal from an input, the output can’t happen, either at all, or efficiently, the computer then has to fall back to what are known as “reference values” stored in a ROM. An example of this in a washing machine, is if the computer can’t determine the water temperature, it can’t heat it correctly.

An example in a car would be if it can’t detect how much fuel is being injected to the electronic injectors, the emissions are affected and it has to fall back to reference values stored in “injection maps” in the ECU as it’d be using too much fuel and it would cause combustion problems.

If you suspect that there’s a fault in one of the circuits in your washing machine it’s usually much easier to test all the components in the circuit before suspecting that the problem lies in the control board. Problems in the wiring network of a machine are much more likely the cause. For example in the drainage circuit you would check the drain pump and the wiring; the heating circuit you would check the element, the thermostat and the wiring. If you then suspect that the problem still lies in the circuit board unfortunately it’s usually quite difficult for inexperienced people to test the board and you’ll actually just need to replace it altogether or consult an electronics guy like me.

The first problem we’re going to look at is program issues. Most modern machines are designed to shut down if they detect a fault somewhere in the system and this is usually accompanied by a fault code. A fault code is displayed on the front of the machine as a combination of letters and lights or numbers. These fault codes vary from one manufacturer to another so it can actually be just as helpful to watch your machine to diagnose where the fault is, such as in the drainage circuit or the heating circuit. When you turn your machine on, the first thing it does is to lock the door via the electronic door lock solenoid and it’s then that it performs a self-check. If in the self-check it detects a fault somewhere in the system it’ll shut down and display a fault code, or if the door doesn’t lock properly it’ll also detect that as a fault and shut down.

Once the machine has passed the self-check stage, it will proceed to fill with water through the fill valves (solenoid valves) at the back. Most stages in a washing machine cycle are programmed to complete within a predetermined time so if your machine doesn’t recognise that it’s filled within a couple of minutes it will usually shut down and display a fault code to stop any flooding occurring. Assuming that’s OK and the machine has filled with water it will then move on to the next stage in the wash cycle. Once the water has filled to the correct level the machine will then start to agitate it and heat it if required by that particular cycle. Once the temperature has been reached the machine will then wash for a certain amount of time before draining the water away and again, this has to happen within a predetermined time so if it doesn’t, the machine will shut down and display a fault code.

Once the water’s drained it will then do a short spin and this is followed by the rinse cycle. The rinse cycle is very similar to the wash cycle, except in the rinse cycle the water isn’t heated; water is brought in to a predetermined level within a certain amount of time, it’s then agitated, before being drained away. Most machines have at least two rinses in the rinse cycle and on the final rinse both solenoid valves at the back of the machine open up and flush any conditioner from the detergent drawer down into the drum. Once the machine has completed the rinse cycle it will prepare for the final spin by balancing the load. It does this by attempting to evenly distribute the weight of the load around the drum by using sensors to detect drum wobble on either side of the drum. However, if the load contains a particularly heavy item – such as a pair of jeans or a towel – amongst an otherwise lighter load, it will attempt to balance that heavier item amongst the load. If it can’t balance the load it will simply refuse to spin or it may just shut down and display a fault code.

However, once the load has been balanced the machine will spin and complete the wash cycle. If your machine is dead and it’s not displaying any lights or anything on the front then you’ll need to check it for continuity. Firstly, just unplug it from the wall and have a look at the fuse inside the plug to make sure it hasn’t blown; once you’ve established that it hasn’t, you’ll need to check for continuity between the plug and the control board. Don’t just replace the fuse and plug back in, the fuse has blown for a reason, and until the reason is found and fixed it will likely blow more fuses.

If you follow the path of the plug in through the machine, some will come through to a filter board, it then passes along to the plug on the control board. Grab a multimeter on a resistance or continuity setting and just check for continuity between the two. If you can see that there’s continuity on both connections, that shows power is getting to the circuit board, but there’s probably a fault inside – the way we need to check is by replacing the board with a new one.

Next, let’s have a look at if your machine is blowing a fuse when you plug it in; usually this is caused by a short circuit somewhere in the machine and the short can either exist in the control board or within components around the machine. You can check very easily for a short if you unplug the machine and, using a multimeter on a resistance reading, check for the short across the plug through live and earth, and live and neutral. If there is a short there it’s going to show up as a resistance reading of less than a couple of ohms. Often the first thing to short is the heating element, so try disconnecting that and testing again for a short circuit; if the short has gone then that would indicate that the short does lie in the element. Obviously you can double check by testing the element itself and for a working element the reading you’re looking for is somewhere between twenty and fifty ohms so anything outside of that reading means you’ll need to replace the element.

On the other hand, if removing the element doesn’t get rid of the short the next thing to disconnect is the circuit board and again, once you’ve done that, check for a short there. If the short still hasn’t gone, move further along the line and try checking on the filter board. If the short still hasn’t gone then then it’s likely to be in the plug and the cable and you’ll need to replace those. To test the element, first disconnect the connector lugs and then turn your meter onto a high resistance setting and measure from earth to one of the terminals – from this you shouldn’t get a reading. Then put your meter onto a low resistance setting and measure across the element – on this one I’m getting a reading of about twenty-seven to twenty-eight ohms, so that indicates that this one is OK.

If your machine is tripping the electricity, the process for diagnosing is largely the same, however it may be that a normal meter won’t show any fault being present. In such a scenario an engineer would use an insulation tester such as a Megger and this produces five-hundred volts for determining where the breakdown has occurred. Again, it’s likely to be due to the heater, or heaters if it’s a washer-dryer appliance, but if the tripping is occurring during the final spin the motor is likely to be at fault, where it’s being worked at its hardest during that part of the cycle. One final thing about control boards and tripping faults is that a lot of the time it can be difficult to conclusively diagnose the fault; sometimes a fault that’s being caused by another component actually appears to be caused by the control board. Similarly, if you’re replacing the control board, many of them now require professional programming on installation.

I’m here to help, don’t be afraid to ask!

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