TideLog Posts Tagged “Hoover”

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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Pete and I fixed one of these today as a callout. We actually fixed the customers computer, and mentioned that we fix consumer and white goods. She said her washer wasn’t working, it was flashing the Delay Start button’s light after running any programme for 3 minutes. The Nextra 7 is full of sensors, so we took a look for her.

The engineer invoked self-test programme was halting when the heaters were started. So, we checked the dryer elements and thermostat, they were fine. The washer tub elements were passing resistance tests. The motor was good, its brushes were clear and the commutator oiled nicely. Resistances were OK so we started to suspect the control board. This contains all the relays for the motor/heater start stop and motor polarity reverse, and the surface mount CPU and timer control IC. Luckily I have a board for one of these spare, as Kassie and I used to have one, so we tried that.

Still no luck. Now we’d checked motor, dryer heater element, washer tub heater element, dryer thermostat cutout switches and control board, plus the water inlet valve solenoid. Next thing was the wiring, or a bad ground. I loosened the wiring harness keeping the wiring away from the dryer fan on the left rear side of the chassis, and the problem made itself obvious to us!

One of the positive wires to the dryer heat channel thermostat was cut cleanly in half, trapped inside the metal harness! The harness was too tight, so when the tub/motor assembly moved on its suspension the wire was being chafed against the harness and it had sheared cleanly in two! We repaired the broken wire with a terminal joint, and all was like clockwork again!

The wiring inside a modern sensor washer dryer is all linked in series, like in a Volvo bus vehicle CAN (Controller Area Network) multiplex setup. Each system and sensor is wired together like a daisy chain, so a failure of the dryer heater or thermostat, for example, will affect the control board even in a cold rinse, as an open circuit is treated as a catastrophic failure, halting the machine in any program. The Nextra 7 uses LED flashes as fault codes, this particular fault was 10 flashes and 5 second pause.

Moral of the  story? Use logical fault finding engineer knowledge. Try everything, start large, down to small. Motor, heater, pumps, control board, then sensors, manual reset thermoswitches, and all wiring. DON’T just do what idiots do on forums (“Oh, it’s the control board!!”) because that’s the stupid newb way of doing it!

And, if you replace an FRU resulting in the problem still occurring, put the old part back, and try something else. Never leave new parts in if they aren’t the cause of the fault, it is pointless cost for the customer, and wasteful, you end up with old used working parts in your van that could fail in the future if fitted somewhere else! This is the general way we do things in IT repair too, as well as consumer goods repair.

Common sense, really. Well, it is to me, I’ve always worked like that.

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